lntens. Care Med. 3, 237-244 (1977)
Inten-qive Care M e d i c i n e 9
Springer-Verlag1977
Inflammation and Host Resistance to Pathogens Robert M. Fauve Unit6 d'Immunophysiologie celhilaire, Institut Pasteur, Paris, France
Among the early events occurring after the entry of pathogens into the tissues, inflammation is one of the mechanisms which helps the host to increase the number and the quality of the weapons against aggressors. The purpose of this short review is to summarize briefly the different stages of an inflammatory reaction and to describe some of the mechanisms by which pathogens escape increased host resistance. Furthermore, it will be shown that a local inflammation, distant from the site of aggression can markedly increase the resistance of the host to pathogens such as bacteria, parasites and tumour cells.
Inflammation Originally defined by this term because of the cardinal signs of erythema, oedema, pain, and local warmth, inflammation actually represents the organism's response to various insults through various neurologic, vascular, humoral, and cellular mechanisms. The complexity and interrelationship of these factors make it difficult to summarize the cascade of events that constitute the inflammatory reaction (Figure 1). A more complete description of inflammation can be found in recently published books and reviews (1-6). We will first describe schematically the inflammatory process and then give details of certain aspects, particularly those that relate to immune responses. Tissue aggression by trauma, infectious agents, injected substances, increased temperature, and radiation initially induces vasodilatation, which is followed rapidly by increased vascular permeability. The latter effect is often associated with morphological changes in capillary endothelial cells. These changes result in platelet adhesion and aggregation and in leukocytic adhesion at the site of cellular alteration. Platelet aggregation coincides with the onset of activation of various steps in blood coagulation releasing mediators that participate in the inflammatory
reaction. After adherence occurs, leukocytes pass through vessel walls into extravascular spaces (diapedesis). Leukocytes (especially polymorphs and, later, monocytes and lymphocytes) are directed to the affected tissue or the irritant by chemotactic factors. Within the extravascular space, polymorphs release metabolic products, or lyse, and this action, in turn, releases enzymes that induce mastocytic degranulation, with subsequent release of new mediators. Monocytes also leave the vessel to phagocytise cellular debris and to be transformed into macrophages. Products of macrophage metabolism or cell lysis then reinforce the inflammatory reaction. Unlike polymorphs and monocytes, very few lymphocytes are found in inflammatory foci, except in peculiar situations. In correlation with leukocyte diapedesis, an exudation of plasma occurs, that contributes to oedema and brings various materials to the site of inflammation, particularly coagulation factors and complement components, which both enhance inflammation. Accumulation at the site of the inflammatory focus of serum components, phagocytic cells, and certain mediators induces an alteration in the lymphatic system that permits entry into the circulation of substances that will act on ar~tibody-forming organs and cells implicated in specific or nonspecific immune reactions. Obviously, several steps contribute to the acute inflammatory reaction. Later, macrophages ingest the inflammatory agent and also eliminate cellular debris. The healing phase is represented by fibroblast proliferation and collagen synthesis. If the causal agent is not easily resorbed, the macrophages are even more important, and, under certain conditions (infection by bacteria), lymphoid cells may accumulate. The transition from acute to chronic inflammation is most marked when inflammation is induced by foreign, poorly resorbed substances like adjuvants (used in immunization). These substances include calcium or aluminium phosphates, mineral oil, and mixtures of mineral oil and mycobacteria (Freund's complete adjuvant). We shall now examine, in the order of their appearance, various factors implicated in inflammation (Fig. 1).
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R. M. Fauve: Inflammation and Host Resistance to Pathogens Platelet Aggregation and Coagulation Even minimal tissue alteration induces in nearby capillaries adhesion of platelets to the capillary endothelium. This adhesion requires thrombin and divalent calcium ions. Adenosine diphosphate released by these platelets promotes adhesion of other platelets which aggregate to cause leukocyte adhesion. At this point, the platelets release serotonin. Platelet thrombus formation produces local coagulation. If thrombin is present, fibrinogen is transformed into fibrin. During these successive phases, some coagulation factors play a role. Thus, Hageman's factor, activated by blood contact with affected vessels, activates the kinin-forming system and increases leukocytic adhesion. Thrombin, a proteolytic enzyme with a molecular weight of 30000, does act on platelets, to stimulate mediator (serotonin) release. Fibrin has a chemotactic role. The plasminogen-plasmin fibrinolytic system acts (through plasmin) on ~2 globulins to produce other mediators, especially kinins (Fig. 2).
Leukocyte Adhesion Soon after platelet aggregation, leukocytes adhere to vascular walls. Margination is enhanced in the presence of fibrin deposits. This phenomenon is not necessarily linked to increased capillary permeability. Once fixed onto endothelial cells, leukocytes (especially polymorphs) and, in lesser numbers, monocytes and lymphocytes may penetrate vessels if inflammation is severe enough (diapedesis).
Increase o f Capillary Permeability Capillaries are composed of endothelial cells tightly linked together by desmosomes. Capillary endothelial cells are surrounded by a basement membrane. Capillary permeability is increased by contraction of endothelial cells caused by defined tissue factors, specific antigens, and, most importantly, mediators like bradykinin, histamine, and serotonin. The kinetics of increased capillary permeability vary according to species, site of activity (tissue), and type of inflammation. Increased vascular permeability induces (plasma) exudation, diapedesis, and extravascular migration of leukocytes. Exudation This phenomenon is the cause of appearance of numerous substances within the extravascular space. These substances include antibodies, bactericidal substances, coagulation factors, and complement components, which also act to perpetuate the inflammatory reaction. Antibodies, in the presence of their corresponding antigen and complement, exert a chemotactic action on lymphocytes and,
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in addition, increase vascular permeability. Bactericidal substances lead to lysis and provoke phagocytic stimulation, with release of some bacterial products, the chemotactic and vasoditatory actions of which have been suggested. The importance of coagulation factors has already been emphasized. Complement components are involved at several levels. Complement activation may be induced by antigen-antibody complexes or by a direct action of plasmin on the C 3 component of complement. In the latter case, plasmin splits a C3 fragment (C 3 a) that has anaphylatoxinic properties. The trimolecular complex (C5, C6, and C7) produced after the interaction of C 1, C4, C2 and C3 has an important chemotactic effect on phagocytic cells.
L e u k o c y t e Diapedesis and Migration We have seen that at the beginning of inflammation, leukocytes adhere to vessels. Polymorphs, monocytes, and lymphocytes penetrate in between endothelial cells to perforate the basement membrane and enter the extravascular Space. The special nature of the extracellular space (collagen and elastic fibres plus mucopolysaccharides) favors cell movement. When leaving the vessels, leukocytes do not migrate preferentially. However, the presence of immune complexes, cellular debris, polymorphs, and monocytes appears to attract these leukocytes. It is important to note that the relative proportions of neutrophils, basophils, eosinophils, monocytes, and lymphocytes vary according to the nature of the inflammatory agent. For example, some parasites induce a selective migration of eosinophilic polymorphs, which also appear in the inflammatory foci secondary to allergic causes. As a consequence, certain metabolites are produced, and variations in antigen and immune complex uptake and in endopyrogen and mediator release are seen. Metabolic products of leukocytes, especially phagocytic cells, cause a fall in local pH, largely due to production of lactic acid by leukocytic glycolysis; antigen and immune complexes are taken up particularly well by certain polymorphs, in particular, eosinophils and macrophages. Macrophages originate from the monocytic transformation that occurs after diapedesis. Antigen uptake is particularly important for particulate antigens (cells, bacteria, parasites). Phagocytic cells degrade and extract antigenic groups, which then directly stimulate antibody synthesis. During phagocytosis or lysis, polymorphs, monocytes, and macrophages may release endopyrogens. These substances, which have a molecular weight between 1.04 and 2 x 104 are proteins. Very low concentrations are effective : levels of 30 to 50 ng exert intense pyrogenicity in the rabbit. These substances are not produced by lymphocytes. Leukocytes release other mediators, including vasoactive amines, proteases or migration-inhibitory factors.
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Inflammatory Mediators These include vasoactive amines, polypeptides and other substances.
lation and, therefore, histamine release. Possibly related to this action is evidence that intradermal injection of PGE 1 and PGE 2 augments capillary permeability following mediator release.
1. Vasoactive Amines
5. Role o f Mediators
Histamine is present in all tissues, with higher concentrations in tissues rich in mastocells. It is present in the granules of mastocells, together with serotonin and heparin. Histamine release from mastocytic granules is induced by proteolytic enzymes, macromolecular substances like dextran, basic compounds (48/80) denaturing agents, heat, decreased pH, and in the presence of antibody-antigen reactions. Histamine is a vasodilator and thus increases capillary permeability. In addition, histamine augments in vitro phagocytic (cell) ingestion, particularly of neutrophil polymorphs. Widely distributed in animals and vegetables, 5 hydroxytryptamine is found chiefly in mammalian mastrocells and platelets and is a strong vasodilator.
Inflammatory mediators exert focal and systemic actions. It is well established that they produce localized vasodilatation and increased capillary permeability. In addition to an effect on lymphatic vessels, they act directly on leukocytes. Thus, nucleotides may augment macrophage pinocytosis, and certain concentrations of bradykinin increase the motility of polymorphs and, especially, macrophages. Preliminary reports indicate that bradykinin may induce leukocyte division. At a distance mediators, especially endopyrogens have an effect on the thermoregulatory area of the hypothalamus. It was recently found that such an action can induce the increased production of acute phase proteins from the liver. It is therefore easy to understand that following an inflammatory reaction in a tissue, many effectors of the resistance against pathogens may increase the resistance of the host. Among humoral effectors, following exudation, increased amounts of complement, lysozyme, interferon, and bactericidal substances are increased as are antibodies. An inflammatory reaction, not only increases the number of polymorphonuclear leukocytes, macrophages, and lymphocytes but, the ability of these cells to deal with aggressors is also stimulated. There are many examples in the literature showing that following an inflammatory reaction, the ability of phagocytes to cope with bacteria or parasites is increased. Another consequence of inflammation is the decrease of extracellular pH, the modification of 02 tension and the release of many products. Among these products, following the disruption of phagocytic cells, many hydrolases are released and some metabolic products such as lactic acid are deleterious for pathogens. Many viruses, bacteria, parasites and tumour cells are not able to survive in such an environment but some pathogens are able, not only to survive but to delay, to decrease or even to inhibit inflammatory reactions.
2. Proteases These enzymes include plasmin, kallikrein, and a globulin permeability factor.
3. Polypeptides Two polypeptides are particularly important in inflammation : a nonapeptide, bradykinin, and a decapeptide, kallidin. These peptides originate from a plasma globulin (kininogen) that is degraded by a protease, kallikrein, and have very important vasodilating effects.
4. Other Substances Adenosine and adenylic acid may be released following burns. They also have a vasodilator effect. Hyaluronidase is found in increased concentration, even in the absence of infection. Its vasomotor role is unclear, but by impairing viscosity, hyaluronidase enhances leukocytic movement. Lactic acid, produced by polymorphs and macrophages, provokes capillary vasodilatation. Prostaglandins were initially isolated from seminal fluid. They derive from prostanoic acid, which itself derives from fatty acids. Several prostaglandins have been identified, all derivatives of prostanoic acid. These prostaglandins are present in numerous tissues, especially in human platelets (prostaglandins E 1 and E z (PGE 1 and PGE2)), which release them in response to thrombin depositions. PGE 1 and PGE 2 induce mastocytic degranu-
Anti-inflammatory Effects of Pathogens Inflammation follows injury of a tissue. Such an injury can be induced by minor trauma or as a consequence of irritating substances in the tissues. The release of these substances is also expected in the presence of parasites and bacteria or of cells which are foreign to the host. It is therefore all the more remarkable that in tissues contaminated with certain bacteria or parasites, and also in
R. M. Fauve: Inflammation and Host Resistance to Pathogens
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tumours or in the pregnant uterus, none or only very carnimoma is not followed by the formation of a granuweak inflammation can be detected. loma; the malignant cells spread directly along the filters of the chamber (16). A correlation was found between the With bacteria, it has been shown that when mice are absence of leukocytic infiltration in the tumour mass and injected subcutaneously with non virulent strains of Staphylococcus aureus, there is an immediate influx of the degree of malignancy (17). More recently, an inverse edema fluid and leukocytes into the infected area. In correlation between malignancy and the content of macrocontrast, when a virulent strain is injected, there is no phages in the tumour was reported (18). This antiinflamoedema or leukocyte response for at least two hours (7). matory activity was found in the supernatant of maligThe substance responsible for such an effect is a muconant cells cultured in vitro (19) and it was shown that peptide residue extracted only from virulent strains which cellular extracts from the tumours of Walker and Noviacts on the Hageman's factor-kinin pathway (8). Other koff exhibit antichimiotactic properties (20). In vitro, bacteria are known to impede the first steps of host rewhen macrophages are incubated with malignant cells, sistance to infection : group A Streptococcus, Vibrio they are not able to interact with tumour cells (19, 21), cholerae, Pseudomonas aeruginosa, Bordetella pertussis, and their ability to spread is decreased (19, 22). Klebsiella pneumoniae, Mycoplasma (9). Similar findings were reported during pregnancy. No Many parasites are known, which do not induce ininflammatory reaction is observed in the pregnant uterus flammatory reactions when alive in the tissues (10-12). despite the fact that trophoblast cells destroy decidual Amoebae destroy liver parenchymal cells without any or cells, and even perforate the blood vessels (23). This lack with a weak inflammatory reaction despite the fact that of inflammation is not restricted to the uterus since it is antibodies produced by the host are known to coat the known that when grafted under the kidney capsule, troamoebae. In onchocerchiasis, despite large numbers of phoblast cells invade kidney tissue without leukocytic inliving microfilariae moving in the cornea, no leukocytic filtration (24). In vitro, it was observed, at the vicinity of infiltration is observed. Similar findings have been retrophoblast cells, that macrophages are unable to spread ported with many animal nematodes parasites (Strongyand become necrotic (19). lofdes papillosus, Trichlostrongylus colubriformis, FilarThese observations indicate that the inhibition of inoiites osleri, Angiostrongylus cantonensis . . . ) and even flammatory reactions and the "paralysis" of leukocytes with insect parasites (13). In schistosomiasis, as shown may allow an "aggressor" to ingraft and later on, to mulby Lichtenberger and Richie in their S.mansoni-rhesus tiply in a host with normal immune reactions. It is well known that either during gestation (25) or following the monkey model, although schistosomulae are seen in lung sections, they do not evoke any cellular reaction. Likewise, inoculation of many tumour ceils (26), the host is able adult worms, in portal vessels do not induce any reaction. to react specifically against foetal or tumour antigens. This lack of inflammation is paradoxical since a cellular reac- Such immune reactions occur with parasites or bacteria. tion is observed with other parasites such as Strongylus Nevertheless, if the vascular permeability is decreased and vulgaris. In preliminary experiments, we found that adult if leukocytes functions are impeded, specific or non worms of S. mansoni, when inserted subcutaneously into specific immune factors should not be able to reach their mice did not induce any inflammatory reaction despite targets. The absence of leukocytes in malignant tumours, the surgical trauma. In contrast, worms killed with glutar in the placenta and at the vicinity of some living paraaldehyde, provoked severe oedema and a large cellular sites seems therefore to result from some common mereaction. These findings led us to look for antiinflammachanism: the ability of some aggressors to repulse the tory substances produced by adult worms. Alive adult vectors of specific immunity, e. g. an immunorepulsion. worms were incubated in tissue culture medium. After Immunorepulsion corresponds to a local immunodefiltration, the supernatant was injected into the peripression which allows embryos, tumour cells, some bactoneal cavity of mice. Control mice received the same teria, and many parasites to survive and grow unharmed medium without incubation with adult worms. Six hours by the host immunological surveillance system. Such a later, the percentage of polymorphonuclear leukocytes local immunodepression results from the action of imin the peritoneal cavity of control mice was found to be munorepeUents synthesized by some aggressors. These greater than 50%. In contrast with the medium in which immunorepeUents are able to prevent inflammatory reworms were incubated, fewer than 20% of polymorphoactions from occurring in the vicinity of the aggressors nonuclear leukocytes were found. Moreover, it was oband to impede the leukocytes to fulfill their functions served that the spreading of macrophages was decreased. (27). In cancer, it is also known that the destruction and Such an aggressive mechanism of defense of pathogens the invasion of adjacent tissues by malignant cells (14) is against the host is certainly one of the earliest weapons not followed by an inflammatory process. Moreover, it of pathogens since the first reaction of defense in primihas been shown that a strong inflammation can be elicittive metazoa is the mobilisation of amoebocytes on the ed by a cotton thread in normal tissues, but not in the site of aggression. This increased number of phagocytic tumours of mice or rats (15). Likewise, the insertion of cells is the equivalent of the cellular mobilisation which a diffusion chamber in the tumour mass of an hepatooccurs during inflammation in vertebrates and which is
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one cornerstone of the resistance of the host against pathogens. One can now wonder if inflammation is not able, at distance, to modify the resistance.
Increased Resistance Against Pathogens Following I n f l a m m a t i o n It has been known for nearly a century that animals are much more resistant to infections if virulent bacteria are injected at the site of an acute inflammation (28). We are not aware that a significant increase of resistance was found when inflammation was induced at a distance from the site of infection. It is also well known that in the preantibiotic era abcesses were induced in patients in order to stimulate their resistance against infectious diseases. Nevertheless these inflammatory reactions were produced following injection o f irritating substances (turpentine oil) or bacteria now known to be able to diffuse from the injection site. In these conditions, it is therefore difficult to dissociate the direct effect of these substances on the immune system from the effects of the inflammatory reaction per se. In order to investigate such effects in experimental models, in our laboratory, it was decided to induce inflammatory reactions with non biodegradable, non diffusible and non antigenic substances. It was also considered that such irritants had to be injected at a site distant from the site o f aggression. For this purpose, mice were injected subcutaneously in the dorsal area with magnesium silicate embeded in a gel of calcium phosphate. Care was taken during the preparation of this irritant and during manipulations o f mice to avoid the presence o f pathogens and pyrogens. Later on, treated and control mice were challenged with virulent Listeria monocytogenes, Schistosoma mansonL and a high malignant tumour: the Lewis carcinoma.
ber of Listeria was counted at different time intervals during the first three days following infection. It was found on the third day that the number of Listeria in the spleen and the liver was respectively 100 and 1000 times less in treated mice than in control animals. This increased resistance is the consequence of an increased bactericidal power of the macrophages. It was also found recently that a fraction can be extracted from the granuloma and that mice injected only three hours before infection can withstand a lethal inoculum of Listeria rnonocytogenes (30).
I n f l a m m a t i o n P r o t e c t s Mice A g a i n s t S c h i s t o s o m a Mansoni (31)
Schistosoma mansoni is one of the parasites responsible for schistosomiasis a disease affecting several hundred millions of inhabitants of the third world. In contrast with contaminated water, furcocercariae of S. mansoni penetrate the skin of men and, as schistosomulae, migrate to the lung. Later on, these schistosomulae transform into adult worms which live in portal veins. Eggs are produced which are later excreted in water from which miracidia are able to infest planorbs. In planorbs, these miracidia transform into furcocercariae which are able to infest men. In the laboratory, it is possible to infest mice during immersion of the tail in a suspension of furcocercariae. Fourty five days later, it is possible to count the number of adult worms in the portal veins. It was found that mice with an inflammatory reaction, in contrast with normal mice can be fully protected against S. mansoni. It is too early to describe the mechanisms which are responsible for such a protection but recent findings indicate that an increased resistance is found in the sldn and in the lungs of treated animals.
I n f l a m m a t i o n I n c r e a s e s the R e s i s t a n c e o f Mice Against Lewis Tumour I n f l a m m a t i o n P r o t e c t s Mice A g a i n s t Listeria Monocytogenes
Listeria monoeytogenes is a gram positive bacteria which, when injected intravenously, is easily cleared from the blood following its ingestion by macrophages from the liver and the spleen. In contrast to many bacteria, Listeria, once in phagocytic cells divides and destroys the macrophages. When control mice and mice with an inflammatory reaction in the dorsal area were infected i.v. with a 10 L.D.so of Listeria, the control mice died, in contrast with treated animals, which survived. In order to explain such an increased resistance, the fate of bacteria was followed after infection. For this purpose, the num-
The Lewis tumour (3 LL) is one of the more malignant murine solid tumours. Once injected into the foot-pad 3 LL cells multiply and induce a tumour. Following the injection of 10 t~ 3 LL cells, metastasis can be Seen six days later in the draining lymph node. Twenty days later, metastases are found in the lung. Until now, specific immunization has been unsuccessful and B.C.G., which can stimulate the host resistance against many experimental tumours is without effect. When the growth of 3 LL tumours is compared in control mice and in mice with an inflammatory reaction (32), it was found that the growth of the tumour was delayed. When the inflammatory reaction is induced one day later the injection of tumour cells, the growth of the tumour starts seven days later than in control mice. In
R. M. Fauve: Inflammation and Host Resistance to Pathogens contrast with controls, no metastases are found in the draining lymph node and 20 days later, no metastases are seen in the lungs of treated mice. Furthermore, in contrast with the tumours of control animals, in tissue sections, leukocyte margination is seen in the tumour's vessels and many histiocytes are seen among the tumour ceils. It was also found that normal macrophages can be activated against tumour cells when they are incubated in the serum from mice having an inflammatory reaction.
Possible Mechanisms E x p l a i n i n g the Increased Host Resistance Following Inflammation These results show that a local inflammatory reaction induced by non biodegradable and non diffusible substances and occurring in a place distant from the site of aggression is able to increase the host resistance against some of the more "virulent" bacteria, parasites and tumour cells. Since the pathogens are never in contact with the inflammatory reaction, these results indicate that some mediators, in the broadest sense of the term may act on pathogens or on the effectors of non specific resistance against pathogens. One can consider the k n o w n mediators of inflammation, the acute phase proteins, tile degradation products and hormones (33). Known mediators of inflammation are serotonin, bradykinin, histamine and prostaglandins. It was found that local injection of serotonin can decrease or even inhibit the growth of melanoma in mice. Bradykinin was found to be a mitogen for lymphocytes, thymocytes and to activate macrophages. Histamine is known to increase the bactericidal activity of polymorphs. Prostaglandin PGE 2 was found to decrease the growth of melanoma in mice and PGF2t~, injected in the site of a tumour induced with dimethylbenzanthracene was found to decrease the rate of growth of the turnout. The biological activity of acute phase proteins is not well known and most of the known biological activity of a t and a 2 glycoproteins is to bind hydrolytic enzymes such as trypsin and chymotrypsin. Nevertheless, it was found quite recently that C. reactive protein which is only synthesized following injury is able to stimulate polymorphonuclear leukocytes and is a mitogen for lymphocytes. Nothing is known of the possible action of degradation products released from the tissues during inflammation. Nevertheless, one has to consider the split products of collagen, the hydrolases and the endopyrogens released by both polymorphonuclear leukocytes and macrophages. It has been shown that peptides released following lysis of collagen are strongly chimiotactic. It is also known that neutral proteases in lower amounts than lectins are mitogenic for lymphocytes. Other degradation products as yet unidentified can play a major role in the non specific stimulation of the immune system following inflammation. Furthermore, as found recently
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in our laboratory, such an inflammation is able to induce a preferential differentiation of bone marrow stem cells into leukocytes. Despite its complexicity, this mechanism of stimulation deserves attention since an inflammatory reaction is able to increase tremendously the host resistance against pathogens. It is already possible to extract "stimulating substances" from mice. Therefore it is reasonable to presume that such substances may exist in man. It would be of great interest to use such therapeutic substances to stimulate non specifically the resistance of man and especially of patients who are too often the victims of their decreased resistance to pathogens. References 1. Florey, H. W. (ed.): General pathology, 4th ed. London: Lloyd-Luke 1970 2. Lepow, I. H., Ward, P. A.: Inflammation, mechanisms and control. New York: Academic Press 1972 3. Rocha e Silva, M., Garcia-Leme, J.: Chemical mediators of the acute inflammatory reaction. Oxford: Pergamon Press 1972 4. Wilkinson, P. C.: Chemotaxis and inflammation. Edinburgh: Churchill Livingstone 1974. 5. Zweifach, B. W., Grant, L., Mc Cluskey, R. F. (ed.): The inflammatory process. 2nd ed. Vols. 2 and 3. New York: Academic Press 1974 6. Ryan, G. B., Majno, G.: Acute inflammation. Amer. J. Pathol. 86, 185 (1977) 7. Hill, M. J.: A staphylococcal aggression. J. Med. Microbiol. 1, 33 (1968) 8. Easmon, C. S. F., Hamilton, I., Glynn, A. A.: Mode of action of a staphylococcal antiinflammatoryfactor. Brit. J. Exp. Path. 54, 638 (1973) 9. Schwab, J. H.: Supression of the immune response by microorganisms. Bact. Rev. 39, 121 (1975). I0. Ciba Foundation Symposium 25: Parasites in the immunized host mechanisms of survival.Amsterdam, New York: Elsevier 1974 11. Poynter, D.: Some tissue reactions to the nematode parasites of animals. Adv. Parasitol. 4, 321 (1964) 12. Duke, B. O. L.: Onchocerciasis. Brit. Med. Bull. 28, 66 (1972) (1972) 13. Salt, G.: The resistance of insect parasitoids to the defence reactions of their hosts. Biol. Rev. 43, 200 (1968) 14. Leighton, J. S., Star, W. J., Mahoney, M. J.: In: Biological interactions in normal and neoplastic growth (eds. M. J. Brennan and W. L. Simpson) Boston: Little, Brown and Co. p. 681, 1961 15. Mahoney, M. J., Leighton, J. S.: The inflammatory response to a foreign body within transplantable tumors. Cancer Res. 22, 334 (1962) 16. Gullino, P. M.: The internal milieu of tumors. Prog. Exp. Tumor 8, 1 (1966) 17. Berg, J. W.: Inflammation and prognosis in breast cancer: a search for host resistance. Cancer Res. 12, 714 (1959) 18. Gauci, C. L., Alexander, P.: The macrophage content of some human tumors. Canc. Letters 1, 29 (1975) 19. Fauve, R. M., Herin, B., Jakob, H., Gaillard, J. A., Jacob, F.: Antiinflammatory effects of murine malignant cells. Proc. Nat. Acad. Sci. USA 71, 4052 (1974) 20. Brozna, J. P., Ward, P. A.: Antileukotactic properties of tumor cells. J. clin. Invest. 56, 616 (1975) 21. Dekaris, D. personal communication
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22. Ax, W. personal communication 23. Bagshawe, K. D.: Choriocarcinoma. London: Edward Arnold 1969 24. Kirby, D. R. S.: Reciprocal transplantation of blastocystes between rats and mice. Nature 194, 785 (1962) 25. Beer, A. E., Billingham, R. E.: Immunobiology of mammalian reproduction. Adv. Immunol. 14, 1 (1970) 26. Cerottini, J. C., Brunner, K. T.: Cell-mediated cytotoxicity, allograft rejection and tumor immunity. Adv. Immunol. 18, 67 (1974) 27. Fauve, R. M.: Immunorepulsion. C. R. Acad. Sci. Paris 282, 1207 (1976) 28. Metchnikoff, E.: L'immunit6 darts les maladies infectieuses. Paris: Masson 1905 29. Fauve, R. M., Hevin, B.: Influence d'une r~action inflammatoire sur la r6sistance de souris ~ l'infection par Listeria monocytogenes et Salmonella typhimurium. C. R. Acad. Sci. Paris 281, 2037 (1975) 30. Fauve, R. M., Hevin, B.: Inflammation et r~sistance antibact~rienne. I. Stimulation des capacit6s d'ingestion et du pouvoir bactericide des macrophages chez des souris porteuses d'une r~action inflammatoire distante du site
d'infection. Ann. Immunol. (Inst. Pasteur), 1977. to be published 31. Fauve, R. M., Herin, B.: Influence d u n e reaction inflammatoire provoqu~e par le BCG ou par un irritant non biodegradable sur la rdsistance des souris ~ la bilharziose. C. R. Acad. Sci. Paris 282, 131 (1976) 32. Fauve, R. M., Herin, B.: Inflammation et r~sistance antitumorale. I. Retard de croissance et inhibition du d~veloppement des m~tastases de la tumeur de Lewis chez des souris porteuses d'une rdaction inflammatoire distante du site d'inoculation des cellules malignes. Ann. Immunol. (Inst. Pasteur) 128C, 923 (1977) 33. Fauve, R. M.: Non specific resistance against pathogens, to be published )
Prof. R. M. Fauve, M. D. Unit6 d'immunophysiologie cellulaire Institut Pasteur 25, rue du Dr. Roux F-75015 Paris Cedex 15, France
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Inten-qive Care M e d i c i n e 9
Springer-Verlag1977
Inflammation and Host Resistance to Pathogens Robert M. Fauve Unit6 d'Immunophysiologie celhilaire, Institut Pasteur, Paris, France
Among the early events occurring after the entry of pathogens into the tissues, inflammation is one of the mechanisms which helps the host to increase the number and the quality of the weapons against aggressors. The purpose of this short review is to summarize briefly the different stages of an inflammatory reaction and to describe some of the mechanisms by which pathogens escape increased host resistance. Furthermore, it will be shown that a local inflammation, distant from the site of aggression can markedly increase the resistance of the host to pathogens such as bacteria, parasites and tumour cells.
Inflammation Originally defined by this term because of the cardinal signs of erythema, oedema, pain, and local warmth, inflammation actually represents the organism's response to various insults through various neurologic, vascular, humoral, and cellular mechanisms. The complexity and interrelationship of these factors make it difficult to summarize the cascade of events that constitute the inflammatory reaction (Figure 1). A more complete description of inflammation can be found in recently published books and reviews (1-6). We will first describe schematically the inflammatory process and then give details of certain aspects, particularly those that relate to immune responses. Tissue aggression by trauma, infectious agents, injected substances, increased temperature, and radiation initially induces vasodilatation, which is followed rapidly by increased vascular permeability. The latter effect is often associated with morphological changes in capillary endothelial cells. These changes result in platelet adhesion and aggregation and in leukocytic adhesion at the site of cellular alteration. Platelet aggregation coincides with the onset of activation of various steps in blood coagulation releasing mediators that participate in the inflammatory
reaction. After adherence occurs, leukocytes pass through vessel walls into extravascular spaces (diapedesis). Leukocytes (especially polymorphs and, later, monocytes and lymphocytes) are directed to the affected tissue or the irritant by chemotactic factors. Within the extravascular space, polymorphs release metabolic products, or lyse, and this action, in turn, releases enzymes that induce mastocytic degranulation, with subsequent release of new mediators. Monocytes also leave the vessel to phagocytise cellular debris and to be transformed into macrophages. Products of macrophage metabolism or cell lysis then reinforce the inflammatory reaction. Unlike polymorphs and monocytes, very few lymphocytes are found in inflammatory foci, except in peculiar situations. In correlation with leukocyte diapedesis, an exudation of plasma occurs, that contributes to oedema and brings various materials to the site of inflammation, particularly coagulation factors and complement components, which both enhance inflammation. Accumulation at the site of the inflammatory focus of serum components, phagocytic cells, and certain mediators induces an alteration in the lymphatic system that permits entry into the circulation of substances that will act on ar~tibody-forming organs and cells implicated in specific or nonspecific immune reactions. Obviously, several steps contribute to the acute inflammatory reaction. Later, macrophages ingest the inflammatory agent and also eliminate cellular debris. The healing phase is represented by fibroblast proliferation and collagen synthesis. If the causal agent is not easily resorbed, the macrophages are even more important, and, under certain conditions (infection by bacteria), lymphoid cells may accumulate. The transition from acute to chronic inflammation is most marked when inflammation is induced by foreign, poorly resorbed substances like adjuvants (used in immunization). These substances include calcium or aluminium phosphates, mineral oil, and mixtures of mineral oil and mycobacteria (Freund's complete adjuvant). We shall now examine, in the order of their appearance, various factors implicated in inflammation (Fig. 1).
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R. M. Fauve: Inflammation and Host Resistance to Pathogens Platelet Aggregation and Coagulation Even minimal tissue alteration induces in nearby capillaries adhesion of platelets to the capillary endothelium. This adhesion requires thrombin and divalent calcium ions. Adenosine diphosphate released by these platelets promotes adhesion of other platelets which aggregate to cause leukocyte adhesion. At this point, the platelets release serotonin. Platelet thrombus formation produces local coagulation. If thrombin is present, fibrinogen is transformed into fibrin. During these successive phases, some coagulation factors play a role. Thus, Hageman's factor, activated by blood contact with affected vessels, activates the kinin-forming system and increases leukocytic adhesion. Thrombin, a proteolytic enzyme with a molecular weight of 30000, does act on platelets, to stimulate mediator (serotonin) release. Fibrin has a chemotactic role. The plasminogen-plasmin fibrinolytic system acts (through plasmin) on ~2 globulins to produce other mediators, especially kinins (Fig. 2).
Leukocyte Adhesion Soon after platelet aggregation, leukocytes adhere to vascular walls. Margination is enhanced in the presence of fibrin deposits. This phenomenon is not necessarily linked to increased capillary permeability. Once fixed onto endothelial cells, leukocytes (especially polymorphs) and, in lesser numbers, monocytes and lymphocytes may penetrate vessels if inflammation is severe enough (diapedesis).
Increase o f Capillary Permeability Capillaries are composed of endothelial cells tightly linked together by desmosomes. Capillary endothelial cells are surrounded by a basement membrane. Capillary permeability is increased by contraction of endothelial cells caused by defined tissue factors, specific antigens, and, most importantly, mediators like bradykinin, histamine, and serotonin. The kinetics of increased capillary permeability vary according to species, site of activity (tissue), and type of inflammation. Increased vascular permeability induces (plasma) exudation, diapedesis, and extravascular migration of leukocytes. Exudation This phenomenon is the cause of appearance of numerous substances within the extravascular space. These substances include antibodies, bactericidal substances, coagulation factors, and complement components, which also act to perpetuate the inflammatory reaction. Antibodies, in the presence of their corresponding antigen and complement, exert a chemotactic action on lymphocytes and,
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in addition, increase vascular permeability. Bactericidal substances lead to lysis and provoke phagocytic stimulation, with release of some bacterial products, the chemotactic and vasoditatory actions of which have been suggested. The importance of coagulation factors has already been emphasized. Complement components are involved at several levels. Complement activation may be induced by antigen-antibody complexes or by a direct action of plasmin on the C 3 component of complement. In the latter case, plasmin splits a C3 fragment (C 3 a) that has anaphylatoxinic properties. The trimolecular complex (C5, C6, and C7) produced after the interaction of C 1, C4, C2 and C3 has an important chemotactic effect on phagocytic cells.
L e u k o c y t e Diapedesis and Migration We have seen that at the beginning of inflammation, leukocytes adhere to vessels. Polymorphs, monocytes, and lymphocytes penetrate in between endothelial cells to perforate the basement membrane and enter the extravascular Space. The special nature of the extracellular space (collagen and elastic fibres plus mucopolysaccharides) favors cell movement. When leaving the vessels, leukocytes do not migrate preferentially. However, the presence of immune complexes, cellular debris, polymorphs, and monocytes appears to attract these leukocytes. It is important to note that the relative proportions of neutrophils, basophils, eosinophils, monocytes, and lymphocytes vary according to the nature of the inflammatory agent. For example, some parasites induce a selective migration of eosinophilic polymorphs, which also appear in the inflammatory foci secondary to allergic causes. As a consequence, certain metabolites are produced, and variations in antigen and immune complex uptake and in endopyrogen and mediator release are seen. Metabolic products of leukocytes, especially phagocytic cells, cause a fall in local pH, largely due to production of lactic acid by leukocytic glycolysis; antigen and immune complexes are taken up particularly well by certain polymorphs, in particular, eosinophils and macrophages. Macrophages originate from the monocytic transformation that occurs after diapedesis. Antigen uptake is particularly important for particulate antigens (cells, bacteria, parasites). Phagocytic cells degrade and extract antigenic groups, which then directly stimulate antibody synthesis. During phagocytosis or lysis, polymorphs, monocytes, and macrophages may release endopyrogens. These substances, which have a molecular weight between 1.04 and 2 x 104 are proteins. Very low concentrations are effective : levels of 30 to 50 ng exert intense pyrogenicity in the rabbit. These substances are not produced by lymphocytes. Leukocytes release other mediators, including vasoactive amines, proteases or migration-inhibitory factors.
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Inflammatory Mediators These include vasoactive amines, polypeptides and other substances.
lation and, therefore, histamine release. Possibly related to this action is evidence that intradermal injection of PGE 1 and PGE 2 augments capillary permeability following mediator release.
1. Vasoactive Amines
5. Role o f Mediators
Histamine is present in all tissues, with higher concentrations in tissues rich in mastocells. It is present in the granules of mastocells, together with serotonin and heparin. Histamine release from mastocytic granules is induced by proteolytic enzymes, macromolecular substances like dextran, basic compounds (48/80) denaturing agents, heat, decreased pH, and in the presence of antibody-antigen reactions. Histamine is a vasodilator and thus increases capillary permeability. In addition, histamine augments in vitro phagocytic (cell) ingestion, particularly of neutrophil polymorphs. Widely distributed in animals and vegetables, 5 hydroxytryptamine is found chiefly in mammalian mastrocells and platelets and is a strong vasodilator.
Inflammatory mediators exert focal and systemic actions. It is well established that they produce localized vasodilatation and increased capillary permeability. In addition to an effect on lymphatic vessels, they act directly on leukocytes. Thus, nucleotides may augment macrophage pinocytosis, and certain concentrations of bradykinin increase the motility of polymorphs and, especially, macrophages. Preliminary reports indicate that bradykinin may induce leukocyte division. At a distance mediators, especially endopyrogens have an effect on the thermoregulatory area of the hypothalamus. It was recently found that such an action can induce the increased production of acute phase proteins from the liver. It is therefore easy to understand that following an inflammatory reaction in a tissue, many effectors of the resistance against pathogens may increase the resistance of the host. Among humoral effectors, following exudation, increased amounts of complement, lysozyme, interferon, and bactericidal substances are increased as are antibodies. An inflammatory reaction, not only increases the number of polymorphonuclear leukocytes, macrophages, and lymphocytes but, the ability of these cells to deal with aggressors is also stimulated. There are many examples in the literature showing that following an inflammatory reaction, the ability of phagocytes to cope with bacteria or parasites is increased. Another consequence of inflammation is the decrease of extracellular pH, the modification of 02 tension and the release of many products. Among these products, following the disruption of phagocytic cells, many hydrolases are released and some metabolic products such as lactic acid are deleterious for pathogens. Many viruses, bacteria, parasites and tumour cells are not able to survive in such an environment but some pathogens are able, not only to survive but to delay, to decrease or even to inhibit inflammatory reactions.
2. Proteases These enzymes include plasmin, kallikrein, and a globulin permeability factor.
3. Polypeptides Two polypeptides are particularly important in inflammation : a nonapeptide, bradykinin, and a decapeptide, kallidin. These peptides originate from a plasma globulin (kininogen) that is degraded by a protease, kallikrein, and have very important vasodilating effects.
4. Other Substances Adenosine and adenylic acid may be released following burns. They also have a vasodilator effect. Hyaluronidase is found in increased concentration, even in the absence of infection. Its vasomotor role is unclear, but by impairing viscosity, hyaluronidase enhances leukocytic movement. Lactic acid, produced by polymorphs and macrophages, provokes capillary vasodilatation. Prostaglandins were initially isolated from seminal fluid. They derive from prostanoic acid, which itself derives from fatty acids. Several prostaglandins have been identified, all derivatives of prostanoic acid. These prostaglandins are present in numerous tissues, especially in human platelets (prostaglandins E 1 and E z (PGE 1 and PGE2)), which release them in response to thrombin depositions. PGE 1 and PGE 2 induce mastocytic degranu-
Anti-inflammatory Effects of Pathogens Inflammation follows injury of a tissue. Such an injury can be induced by minor trauma or as a consequence of irritating substances in the tissues. The release of these substances is also expected in the presence of parasites and bacteria or of cells which are foreign to the host. It is therefore all the more remarkable that in tissues contaminated with certain bacteria or parasites, and also in
R. M. Fauve: Inflammation and Host Resistance to Pathogens
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tumours or in the pregnant uterus, none or only very carnimoma is not followed by the formation of a granuweak inflammation can be detected. loma; the malignant cells spread directly along the filters of the chamber (16). A correlation was found between the With bacteria, it has been shown that when mice are absence of leukocytic infiltration in the tumour mass and injected subcutaneously with non virulent strains of Staphylococcus aureus, there is an immediate influx of the degree of malignancy (17). More recently, an inverse edema fluid and leukocytes into the infected area. In correlation between malignancy and the content of macrocontrast, when a virulent strain is injected, there is no phages in the tumour was reported (18). This antiinflamoedema or leukocyte response for at least two hours (7). matory activity was found in the supernatant of maligThe substance responsible for such an effect is a muconant cells cultured in vitro (19) and it was shown that peptide residue extracted only from virulent strains which cellular extracts from the tumours of Walker and Noviacts on the Hageman's factor-kinin pathway (8). Other koff exhibit antichimiotactic properties (20). In vitro, bacteria are known to impede the first steps of host rewhen macrophages are incubated with malignant cells, sistance to infection : group A Streptococcus, Vibrio they are not able to interact with tumour cells (19, 21), cholerae, Pseudomonas aeruginosa, Bordetella pertussis, and their ability to spread is decreased (19, 22). Klebsiella pneumoniae, Mycoplasma (9). Similar findings were reported during pregnancy. No Many parasites are known, which do not induce ininflammatory reaction is observed in the pregnant uterus flammatory reactions when alive in the tissues (10-12). despite the fact that trophoblast cells destroy decidual Amoebae destroy liver parenchymal cells without any or cells, and even perforate the blood vessels (23). This lack with a weak inflammatory reaction despite the fact that of inflammation is not restricted to the uterus since it is antibodies produced by the host are known to coat the known that when grafted under the kidney capsule, troamoebae. In onchocerchiasis, despite large numbers of phoblast cells invade kidney tissue without leukocytic inliving microfilariae moving in the cornea, no leukocytic filtration (24). In vitro, it was observed, at the vicinity of infiltration is observed. Similar findings have been retrophoblast cells, that macrophages are unable to spread ported with many animal nematodes parasites (Strongyand become necrotic (19). lofdes papillosus, Trichlostrongylus colubriformis, FilarThese observations indicate that the inhibition of inoiites osleri, Angiostrongylus cantonensis . . . ) and even flammatory reactions and the "paralysis" of leukocytes with insect parasites (13). In schistosomiasis, as shown may allow an "aggressor" to ingraft and later on, to mulby Lichtenberger and Richie in their S.mansoni-rhesus tiply in a host with normal immune reactions. It is well known that either during gestation (25) or following the monkey model, although schistosomulae are seen in lung sections, they do not evoke any cellular reaction. Likewise, inoculation of many tumour ceils (26), the host is able adult worms, in portal vessels do not induce any reaction. to react specifically against foetal or tumour antigens. This lack of inflammation is paradoxical since a cellular reac- Such immune reactions occur with parasites or bacteria. tion is observed with other parasites such as Strongylus Nevertheless, if the vascular permeability is decreased and vulgaris. In preliminary experiments, we found that adult if leukocytes functions are impeded, specific or non worms of S. mansoni, when inserted subcutaneously into specific immune factors should not be able to reach their mice did not induce any inflammatory reaction despite targets. The absence of leukocytes in malignant tumours, the surgical trauma. In contrast, worms killed with glutar in the placenta and at the vicinity of some living paraaldehyde, provoked severe oedema and a large cellular sites seems therefore to result from some common mereaction. These findings led us to look for antiinflammachanism: the ability of some aggressors to repulse the tory substances produced by adult worms. Alive adult vectors of specific immunity, e. g. an immunorepulsion. worms were incubated in tissue culture medium. After Immunorepulsion corresponds to a local immunodefiltration, the supernatant was injected into the peripression which allows embryos, tumour cells, some bactoneal cavity of mice. Control mice received the same teria, and many parasites to survive and grow unharmed medium without incubation with adult worms. Six hours by the host immunological surveillance system. Such a later, the percentage of polymorphonuclear leukocytes local immunodepression results from the action of imin the peritoneal cavity of control mice was found to be munorepeUents synthesized by some aggressors. These greater than 50%. In contrast with the medium in which immunorepeUents are able to prevent inflammatory reworms were incubated, fewer than 20% of polymorphoactions from occurring in the vicinity of the aggressors nonuclear leukocytes were found. Moreover, it was oband to impede the leukocytes to fulfill their functions served that the spreading of macrophages was decreased. (27). In cancer, it is also known that the destruction and Such an aggressive mechanism of defense of pathogens the invasion of adjacent tissues by malignant cells (14) is against the host is certainly one of the earliest weapons not followed by an inflammatory process. Moreover, it of pathogens since the first reaction of defense in primihas been shown that a strong inflammation can be elicittive metazoa is the mobilisation of amoebocytes on the ed by a cotton thread in normal tissues, but not in the site of aggression. This increased number of phagocytic tumours of mice or rats (15). Likewise, the insertion of cells is the equivalent of the cellular mobilisation which a diffusion chamber in the tumour mass of an hepatooccurs during inflammation in vertebrates and which is
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one cornerstone of the resistance of the host against pathogens. One can now wonder if inflammation is not able, at distance, to modify the resistance.
Increased Resistance Against Pathogens Following I n f l a m m a t i o n It has been known for nearly a century that animals are much more resistant to infections if virulent bacteria are injected at the site of an acute inflammation (28). We are not aware that a significant increase of resistance was found when inflammation was induced at a distance from the site of infection. It is also well known that in the preantibiotic era abcesses were induced in patients in order to stimulate their resistance against infectious diseases. Nevertheless these inflammatory reactions were produced following injection o f irritating substances (turpentine oil) or bacteria now known to be able to diffuse from the injection site. In these conditions, it is therefore difficult to dissociate the direct effect of these substances on the immune system from the effects of the inflammatory reaction per se. In order to investigate such effects in experimental models, in our laboratory, it was decided to induce inflammatory reactions with non biodegradable, non diffusible and non antigenic substances. It was also considered that such irritants had to be injected at a site distant from the site o f aggression. For this purpose, mice were injected subcutaneously in the dorsal area with magnesium silicate embeded in a gel of calcium phosphate. Care was taken during the preparation of this irritant and during manipulations o f mice to avoid the presence o f pathogens and pyrogens. Later on, treated and control mice were challenged with virulent Listeria monocytogenes, Schistosoma mansonL and a high malignant tumour: the Lewis carcinoma.
ber of Listeria was counted at different time intervals during the first three days following infection. It was found on the third day that the number of Listeria in the spleen and the liver was respectively 100 and 1000 times less in treated mice than in control animals. This increased resistance is the consequence of an increased bactericidal power of the macrophages. It was also found recently that a fraction can be extracted from the granuloma and that mice injected only three hours before infection can withstand a lethal inoculum of Listeria rnonocytogenes (30).
I n f l a m m a t i o n P r o t e c t s Mice A g a i n s t S c h i s t o s o m a Mansoni (31)
Schistosoma mansoni is one of the parasites responsible for schistosomiasis a disease affecting several hundred millions of inhabitants of the third world. In contrast with contaminated water, furcocercariae of S. mansoni penetrate the skin of men and, as schistosomulae, migrate to the lung. Later on, these schistosomulae transform into adult worms which live in portal veins. Eggs are produced which are later excreted in water from which miracidia are able to infest planorbs. In planorbs, these miracidia transform into furcocercariae which are able to infest men. In the laboratory, it is possible to infest mice during immersion of the tail in a suspension of furcocercariae. Fourty five days later, it is possible to count the number of adult worms in the portal veins. It was found that mice with an inflammatory reaction, in contrast with normal mice can be fully protected against S. mansoni. It is too early to describe the mechanisms which are responsible for such a protection but recent findings indicate that an increased resistance is found in the sldn and in the lungs of treated animals.
I n f l a m m a t i o n I n c r e a s e s the R e s i s t a n c e o f Mice Against Lewis Tumour I n f l a m m a t i o n P r o t e c t s Mice A g a i n s t Listeria Monocytogenes
Listeria monoeytogenes is a gram positive bacteria which, when injected intravenously, is easily cleared from the blood following its ingestion by macrophages from the liver and the spleen. In contrast to many bacteria, Listeria, once in phagocytic cells divides and destroys the macrophages. When control mice and mice with an inflammatory reaction in the dorsal area were infected i.v. with a 10 L.D.so of Listeria, the control mice died, in contrast with treated animals, which survived. In order to explain such an increased resistance, the fate of bacteria was followed after infection. For this purpose, the num-
The Lewis tumour (3 LL) is one of the more malignant murine solid tumours. Once injected into the foot-pad 3 LL cells multiply and induce a tumour. Following the injection of 10 t~ 3 LL cells, metastasis can be Seen six days later in the draining lymph node. Twenty days later, metastases are found in the lung. Until now, specific immunization has been unsuccessful and B.C.G., which can stimulate the host resistance against many experimental tumours is without effect. When the growth of 3 LL tumours is compared in control mice and in mice with an inflammatory reaction (32), it was found that the growth of the tumour was delayed. When the inflammatory reaction is induced one day later the injection of tumour cells, the growth of the tumour starts seven days later than in control mice. In
R. M. Fauve: Inflammation and Host Resistance to Pathogens contrast with controls, no metastases are found in the draining lymph node and 20 days later, no metastases are seen in the lungs of treated mice. Furthermore, in contrast with the tumours of control animals, in tissue sections, leukocyte margination is seen in the tumour's vessels and many histiocytes are seen among the tumour ceils. It was also found that normal macrophages can be activated against tumour cells when they are incubated in the serum from mice having an inflammatory reaction.
Possible Mechanisms E x p l a i n i n g the Increased Host Resistance Following Inflammation These results show that a local inflammatory reaction induced by non biodegradable and non diffusible substances and occurring in a place distant from the site of aggression is able to increase the host resistance against some of the more "virulent" bacteria, parasites and tumour cells. Since the pathogens are never in contact with the inflammatory reaction, these results indicate that some mediators, in the broadest sense of the term may act on pathogens or on the effectors of non specific resistance against pathogens. One can consider the k n o w n mediators of inflammation, the acute phase proteins, tile degradation products and hormones (33). Known mediators of inflammation are serotonin, bradykinin, histamine and prostaglandins. It was found that local injection of serotonin can decrease or even inhibit the growth of melanoma in mice. Bradykinin was found to be a mitogen for lymphocytes, thymocytes and to activate macrophages. Histamine is known to increase the bactericidal activity of polymorphs. Prostaglandin PGE 2 was found to decrease the growth of melanoma in mice and PGF2t~, injected in the site of a tumour induced with dimethylbenzanthracene was found to decrease the rate of growth of the turnout. The biological activity of acute phase proteins is not well known and most of the known biological activity of a t and a 2 glycoproteins is to bind hydrolytic enzymes such as trypsin and chymotrypsin. Nevertheless, it was found quite recently that C. reactive protein which is only synthesized following injury is able to stimulate polymorphonuclear leukocytes and is a mitogen for lymphocytes. Nothing is known of the possible action of degradation products released from the tissues during inflammation. Nevertheless, one has to consider the split products of collagen, the hydrolases and the endopyrogens released by both polymorphonuclear leukocytes and macrophages. It has been shown that peptides released following lysis of collagen are strongly chimiotactic. It is also known that neutral proteases in lower amounts than lectins are mitogenic for lymphocytes. Other degradation products as yet unidentified can play a major role in the non specific stimulation of the immune system following inflammation. Furthermore, as found recently
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in our laboratory, such an inflammation is able to induce a preferential differentiation of bone marrow stem cells into leukocytes. Despite its complexicity, this mechanism of stimulation deserves attention since an inflammatory reaction is able to increase tremendously the host resistance against pathogens. It is already possible to extract "stimulating substances" from mice. Therefore it is reasonable to presume that such substances may exist in man. It would be of great interest to use such therapeutic substances to stimulate non specifically the resistance of man and especially of patients who are too often the victims of their decreased resistance to pathogens. References 1. Florey, H. W. (ed.): General pathology, 4th ed. London: Lloyd-Luke 1970 2. Lepow, I. H., Ward, P. A.: Inflammation, mechanisms and control. New York: Academic Press 1972 3. Rocha e Silva, M., Garcia-Leme, J.: Chemical mediators of the acute inflammatory reaction. Oxford: Pergamon Press 1972 4. Wilkinson, P. C.: Chemotaxis and inflammation. Edinburgh: Churchill Livingstone 1974. 5. Zweifach, B. W., Grant, L., Mc Cluskey, R. F. (ed.): The inflammatory process. 2nd ed. Vols. 2 and 3. New York: Academic Press 1974 6. Ryan, G. B., Majno, G.: Acute inflammation. Amer. J. Pathol. 86, 185 (1977) 7. Hill, M. J.: A staphylococcal aggression. J. Med. Microbiol. 1, 33 (1968) 8. Easmon, C. S. F., Hamilton, I., Glynn, A. A.: Mode of action of a staphylococcal antiinflammatoryfactor. Brit. J. Exp. Path. 54, 638 (1973) 9. Schwab, J. H.: Supression of the immune response by microorganisms. Bact. Rev. 39, 121 (1975). I0. Ciba Foundation Symposium 25: Parasites in the immunized host mechanisms of survival.Amsterdam, New York: Elsevier 1974 11. Poynter, D.: Some tissue reactions to the nematode parasites of animals. Adv. Parasitol. 4, 321 (1964) 12. Duke, B. O. L.: Onchocerciasis. Brit. Med. Bull. 28, 66 (1972) (1972) 13. Salt, G.: The resistance of insect parasitoids to the defence reactions of their hosts. Biol. Rev. 43, 200 (1968) 14. Leighton, J. S., Star, W. J., Mahoney, M. J.: In: Biological interactions in normal and neoplastic growth (eds. M. J. Brennan and W. L. Simpson) Boston: Little, Brown and Co. p. 681, 1961 15. Mahoney, M. J., Leighton, J. S.: The inflammatory response to a foreign body within transplantable tumors. Cancer Res. 22, 334 (1962) 16. Gullino, P. M.: The internal milieu of tumors. Prog. Exp. Tumor 8, 1 (1966) 17. Berg, J. W.: Inflammation and prognosis in breast cancer: a search for host resistance. Cancer Res. 12, 714 (1959) 18. Gauci, C. L., Alexander, P.: The macrophage content of some human tumors. Canc. Letters 1, 29 (1975) 19. Fauve, R. M., Herin, B., Jakob, H., Gaillard, J. A., Jacob, F.: Antiinflammatory effects of murine malignant cells. Proc. Nat. Acad. Sci. USA 71, 4052 (1974) 20. Brozna, J. P., Ward, P. A.: Antileukotactic properties of tumor cells. J. clin. Invest. 56, 616 (1975) 21. Dekaris, D. personal communication
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22. Ax, W. personal communication 23. Bagshawe, K. D.: Choriocarcinoma. London: Edward Arnold 1969 24. Kirby, D. R. S.: Reciprocal transplantation of blastocystes between rats and mice. Nature 194, 785 (1962) 25. Beer, A. E., Billingham, R. E.: Immunobiology of mammalian reproduction. Adv. Immunol. 14, 1 (1970) 26. Cerottini, J. C., Brunner, K. T.: Cell-mediated cytotoxicity, allograft rejection and tumor immunity. Adv. Immunol. 18, 67 (1974) 27. Fauve, R. M.: Immunorepulsion. C. R. Acad. Sci. Paris 282, 1207 (1976) 28. Metchnikoff, E.: L'immunit6 darts les maladies infectieuses. Paris: Masson 1905 29. Fauve, R. M., Hevin, B.: Influence d'une r~action inflammatoire sur la r6sistance de souris ~ l'infection par Listeria monocytogenes et Salmonella typhimurium. C. R. Acad. Sci. Paris 281, 2037 (1975) 30. Fauve, R. M., Hevin, B.: Inflammation et r~sistance antibact~rienne. I. Stimulation des capacit6s d'ingestion et du pouvoir bactericide des macrophages chez des souris porteuses d'une r~action inflammatoire distante du site
d'infection. Ann. Immunol. (Inst. Pasteur), 1977. to be published 31. Fauve, R. M., Herin, B.: Influence d u n e reaction inflammatoire provoqu~e par le BCG ou par un irritant non biodegradable sur la rdsistance des souris ~ la bilharziose. C. R. Acad. Sci. Paris 282, 131 (1976) 32. Fauve, R. M., Herin, B.: Inflammation et r~sistance antitumorale. I. Retard de croissance et inhibition du d~veloppement des m~tastases de la tumeur de Lewis chez des souris porteuses d'une rdaction inflammatoire distante du site d'inoculation des cellules malignes. Ann. Immunol. (Inst. Pasteur) 128C, 923 (1977) 33. Fauve, R. M.: Non specific resistance against pathogens, to be published )
Prof. R. M. Fauve, M. D. Unit6 d'immunophysiologie cellulaire Institut Pasteur 25, rue du Dr. Roux F-75015 Paris Cedex 15, France
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