Clinical Allergy, 1979, Volume 9, pages 659-668
Immunological mechanisms in pulmonary diseases
J. E. SALVAGGIO Tulane University, Department of Medicine, New Orleans, U.S.A. (Received 1 June 1979: accepted 7 June 1979)
Although the subject of this symposium, IgE and Mechanisms in Immediate Hypersensitivity, is applicable to most of the common atopic respiratory diseases, there are many other respiratory diseases that are not necessarily IgE mediated. In this talk I shall briefiy touch on the immunological mechanisms involved in the pathogenesis of some of these diseases including allergic alveoiitis (hypersensitivity pneumonitis), the eosinophilic pneumonias and pulmonary fibrosis associated with certain connective tissue, inorganic dust, and occupational diseases. Allergic alveoiitis I should like to limit this term to include those alveolar filling and interstitial pulmonary diseases that result from prolonged exposure to large quantities of finely disbursed organic dusts (of animal protein, actinomycete or fungal origin). These diseases are generally characterized by several common features which include the following: (1) Histologically they are composed primarily of mononuclear cell interstitial and alveolar infiltrates; (2) they involve primarily peripheral airways (alveoli and interstitial tissue); (3) granuloma formation is often a prominent histological feature; (4) systemic involvement as often noted in other granulomatous interstitial pulmonary diseases such as sarcoidosis is not present; (5) they are uniformly associated with serum precipitating antibodies against the appropriate offending organic dust; (6) in vitro correlates of cell mediated or delayed hypersensitivity indicative of lymphokine production are usually positive in symptomatic patients; (7) the diseases are associated with elevated serum levels of IgG, A and M, but IgE levels are usually normal and there is no eosinophilia; (8) large numbers of alveolar cells with the characteristics of activated macrophages are characteristically found within the pulmonary lesions. Many significant recent advances in our knowledge of this disease entity have been made in the area of pathogenesis. The antigens involved have been shown to exert several important biological effects. These include: (1) non-specific activation of the alternative pathway of complement and of alveolar macrophages; (2) a non-specific Correspondence: Dr J. E. Salvaggio, Tulane University, Department of Medicine, Clinical Immunology Section, 1700 Perdido Street, New Orleans, LA 70112, U.S.A. 0009-9090/79/HOO-0659$02.00
© 1979 Blackwell Scientific Publications.
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adjuvant and mitogenic effect; (3) a specific humoral and cellular immune response (serum antibody and lymphokine production); (4) potential to induce tissue destruction (macrophage lysosomal enzyme release). Factors which predispose toward development of this disease are poorly understood. The prevalence of atopic disease is not increased and serum IgE levels and eosinophil counts are typically normal. There is, however, evidence for a possible genetically determined susceptibility. HLA-BW40 has been found with increased frequency in pigeon breeders' disease Allen et al., 1975; Flaherty et al., 1975; Rittner, Sennekamp & Vogel, 1975). Since these antigens are closely linked to immune responses (IR) genes in the major histocompatibility complex, the increased frequency of the B. locus may suggest the presence of an IR gene governing abnormal reactivity to some of the offending aetioiogical organic dusts. Some of the aetioiogical agents in allergic alveoiitis can induce non-specific pulmonary inflammation via activation of the alternative complement pathway or a non-specific adjuvant effect (Bice et al., 1977; Edwards, Baker & Davies, 1974). It has also been determined that induction of prior inflammation of the lung with agents such as BCG, followed by challenge with organic dust or animal protein antigens can induce granulomatous pulmonary lesions resembling those of allergic alveoiitis in association with demonstrable 'local' pulmonary cell mediated hypersensitivity. If these same antigens are administered in a non-particulate form or without prior induction of pulmonary infiammation, lesions are not produced (Moore, Heasley & Fink, 1975). Studies in man and animal models have contributed greatly to our understanding of specific immune responses to aetioiogical antigens in allergic alveoiitis. Although IgE mediated hypersensitivity appears to be of little importance in classical granulomatous allergic alveoiitis, many patients with certain forms of this disease such as pigeon breeders' or bird fanciers' lung demonstrate immediate weal and fiare skin reactions to crude avian antigens. Occasional immediate type asthmatic responses have also occurred following bronchoprovocation challenge testing with these antigens. There is also indirect evidence that cytotoxic (type II) allergic tissue injury may be operative in disease pathogenesis based on demonstration of actinomycete antigen, immunoglobulin and complement components in bronchial walls and on the surface of alveolar macrophages in lung biopsy specimens from patients with farmers' lung (Wenzel, Emmanuel & Gray, 1971). According to this hypothesis soluble inhaled antigen absorbed onto alveolar macrophages and bronchial lining cells would produce direct complement-dependent cell injury at the alveolar interstitial and bronchial level in the presence of specific antibody. Evidence for immune complexes being operative in the pathogenesis of this disease is considerably stronger and has traditionally represented the conventional wisdom in discussing pathogenesis of this disease. IgG precipitating antibody specific for the offending organic dust is present in the serum of patients with the disease and its presence often correlates with intensity of exposure. In the case of some antigens, skin testing induces both early weal and fiare and late (4 to 8 h) Arthus type reactions characterized by necrotizing vasculitis, deposition of complement and immunoglobulin in vessel walls (Pepys, 1969). Symptoms that occur following bronchoprovocation challenge testing also develop after a 4 or 8 hr latent period in many cases closely paralleling the time course observed with the Arthus reaction. In addition, some early lung biopsy specimens obtained from patients with the disease have revealed the presence of antigen, immunoglobulins, and complement deposition by immunofiuor-
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escence as well as necrotizing vasculitis (Ghose et al., 1974; Barrowcliff & Arblaster, 19.68). Interpretation of the above data is controversial, however, since precipitins are present in a large percentage of exposed but asymptomatic subjects and the mononuclear cell and granulomatous infiltrates seen in most cases of allergic alveoiitis are substantially different from the vasculitis lesions seen in other immune complex diseases of man. It is, however, possible that immune complexes can activate alveolar macrophages to secrete hydrolytic enzymes and it is known that insoluble antigen antibody complexes not readily digested by lysospmal enzymes may lead to granuloma formation (Germuth, 1961; Hargreave & Pepys, 1972). Many recent animal models have focused on defining the possible contribution of cell mediated or type IV hypersensitivity in the pathogenesis of this disease since the pulmonary histopathology greatly resembles that of cell mediated hypersensitivity reactions. Studies in man have demonstrated that lymphokine production occurs after peripheral blood or bronchoalveolar lymphocytes are exposed to both avian and/or actinomycete antigens and in some forms of allergic alveoiitis lymphokine production appears to correlate with disease activity. Several animal models of the disease have also clearly demonstrated lymphokine production at the bronchoalveolar level (Salvaggio et al., 1975). In addition, pulmonary lesions resembling those seen in the human disease have been produced after transfer of specifically sensitized lymph node cells followed by aerosol or intratracheal challenge with appropriate antigen (Bice, Salvaggio & Hoffman, 1976). Such lesions have generally not been successfully transfered with hyperimmune serum. Since it is apparent that local, organ restricted, immune mechanisms may be operative at the pulmonary level with or without systemic manifestations of sensitization, studies of bronchoalveolar lavage specimens and cells in animal models of allergic alveoiitis and in some human cases have been undertaken. Reynolds and co-workers noted a higher proportion of lymphocytes, higher IgE and IgM levels and higher T/B cell ratios in patients with allergic alveoiitis when compared with control subjects (Reynolds et al., 1977). In other studies of allergic alveoiitis in man, lymphokine production has been demonstrated by bronchoalveolar cells while peripheral cells failed to demonstrate reactivity to the same antigen (Schuyler, Thigpen & Salvaggio, 1978). Attempts to have been made to correlate development of alveoiitis lesions with immunological events in other animal models. In one study of this type, repeated respiratory tract exposure of rabbits to actinomycete antigen has lead to the development of pulmonary lesions compatable with those of human allergic alveoiitis. The early lesions were composed predominantly of interstitial, peribronchial and intraalveolar mononuclear cells and the later lesions characterized by granuloma and giant cell formation, with most animals demonstrating complete resolution of lesions by 21 to 30 days. In these animals lavage studies indicated a striking increase in number of bronchoalveolar cells after intratracheal installation of particulate actinomycete antigen. Many of these cells demonstrated the morphology of immature or young macrophages containing few phagolysosomes, suggesting that they were recruited in response to lung injury. Alveolar macrophages in this model also showed evidence of 'activation' morphologically, metabolically and with regard to phagocytic and bactericidal activity (Harris, Bice & Salvaggrio, 1976). Following spontaneous regression of pulmonary infiltrates, both pulmonary granulomatous lesions and the state of macrophage activation could also be specifically 'recalled' by challenge with actinomycete antigen via the respiratory tract route.
662 J. E. Salvaggio Since most organic dusts are efiicient activators of the alternative complement pathway, it may be that formation of complement split products such as C3B which are known to induce macrophage lysosomal enzyme release might explain some of the early non-specific lesions of allergic alveoiitis. Since lysosomal enzymes can in turn cleave further C3, a mechanism for continued macrophage activation via an 'amplification loop' process is operative and it is conceivable that pulmonary granulomas containing macrophages with ingested organic dust antigen may evolve in part through this type mechanism. Indeed, Schorlemmer and associates have formulated an hypothesis for the development of allergic alveoiitis that postulates the initial activation of complement by inhaled organic dust antigen with subsequent generation of chemotactic factors and the operation of such an 'amplification loop' resulting in non-specific inflammation (Schorlemmer et al., 1977). In addition, we would propose other immunologically specific mechanisms that could equally account for granuloma formation involving sensitized bronchoalveolar B and T cells. For example, the formation of local immune complexes, which have been demonstrated in animal models of this disease, could lead to activation of alveolar macrophages following ingestion, or could directly induce granuloma formation as has been shown long ago by Germuth (1961). Spector & Heesom (1969). Additionally, sensitized bronchoalveolar T cells which are known to secrete lymphokines in animal models of this disease might participate and produce further lymphokine induced macrophage activation. In any event, the pathogenetic focal point of this hypothesis would be the activated alveolar macrophage which would serve as a functional link between the inhaled offending organic dust antigen and the subsequent mononuclear cell and granulomatous pulmonary lesions. Thus, according to this hypothesis through immunologically specific as well as non-specific processes involving locally formed immune complexes, lymphokine production, and alternative pathway complement activation, pulmonary inflammation would persist as long as antigen is present. According to this hypothesis it would also be possible that persistent inflammation could result in fibrosis via a macrophage mediated influence on fibroblasts by soluble mediators. Eosinophilie pneumonias If one adapts the term eosinophilic pneumonias to include all lung diseases characterized by roentgenographic evidence of pulmonary infiltrates accompanied by either peripheral blood eosinophilia or eosinophilic infiltrative lung disease, one might conveniently divide these diseases into asthmatic and non-asthmatic varieties as illustrated in Table 1. This classification presupposes the importance of host airways lability as a susceptibility factor despite the occasional exception. The classification accounts for major conceptual differences in the eosinophilic penumonias and can be useful in understanding disease mechanisms. Little new information is available on the pathogenesis of the eosinophilic pneumonias with the exception of the asthmatic varieties particularly allergic bronchopulmonary aspergillosis (ABA) (Hinson, Moon & Plummer, 1952) and even this disease is still defined in nebulous terms. This disease has been extensively reviewed and in this summary we will concentrate only briefly on pathogenesis which may serve as a model for some of the other eosinophilic pneumonias when appropriate antigens have been identified. Unlike allergic alveoiitis there have been few animal models of this disease. In studies of man, however, employing crude extracts of mat and spores from Asper-
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Table 1. Eosinophilic pneumonias
Asthmatic
Non-asthmatic
1. Allergic bronchopulmonary aspergillosis
Infection and infestation (Loeffler's Syndrome and chronic eosinophilic pneumonia Drugs and chemicals Eosinophilic granuloma of lung
2. Tropical eosinophilia 3. Pulmonary vasculitis (Polyarteritis nodosa and allergic granulomatous angiilis) 4. —
Leukocytic neoplasms
gillus cultures as antigen, characteristic positive skin responses consisting of an immediate weal and flare reaction followed by a late (4 to 8 hr) reaction have been noted. In a study of twenty subjects with ABA all demonstrated an immediate weal and flare reaction and 33% demonstrated the late reaction (Rosenberg et al., 1977). The detection of serum precipitating antibody against A. fumigatus antigen by simple Ouchterlony gel diffusion is also characteristic of ABA in over 50% of the cases. Anti-Aspergillus antibodies can, however, be detected in the sera of many normal individuals .when sensitive primary binding assays are used, suggesting that the population-atlarge have anti-fungal antibody as a reflection of environmental exposure to ubiquitous fungal antigens. In addition, patients with ABA have marked peripheral blood and sputum eosinophilia and elevated total serum IgE antibody levels (Patterson & Roberts, 1974) which parallel diseases activity. In spite of high IgE levels, however, the amount of specific IgE antibody directed against A. fumigatus is not always extremely elevated. It is well known, based on experimental evidence in the rabbit, that antigen induced IgE mediated release of histamine can facilitate egress of circulating immune complexes into vascular walls and tissues with resultant production of infiammation through activation of the classical complement pathway and such a mechanism has been thought to be operative in production of lesions in allergic bronchopulmonary aspergillosis. Alternatively, intense IgE immediate reactions might result in accumulations of tissue eosinophils via the release of mediators such as eosinophilic chemotactic factor of anaphylaxis (ECFA) as has been proposed for late 'IgE dependent' reactions in general. The existence of either of these mechanisms in ABA is supported by the clinical observations that disodium cromoglycate, a known inhibitor of IgE mediated release of histamine can block both the immediate and late asthmatic reactions following bronchoprovocation challenge testing in these patients (McCarthy & Pepys, 1971, a, b). In addition it has been shown in passive transfer studies involving primates that infusion of serum containing both precipitating and reaginic antibody followed by challenge leads to pulmonary lesions compatible with those of ABA, whereas the administration of serum rich in reagins only, without precipitins, fails to transfer lesions upon challenge (Goibert & Patterson, 1970). In spite of the evidence for an exclusive humoral mechanism in this disease, other data indicate the presence of antigen induced lymphocyte transformation to Aspergillus antigen in symptomatic patients and not in control subjects. The interpretation of these data is unclear at present. The pathogenesis of other eosinophilic pneumonias is even more uncertain than that of ABA. In tropical eosinophilia the hypothesis that the disease results from an
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immunological host response that facilitates entrapment of microfilaria in tissues and precludes their circulation in the blood is favoured. In this disease, support for host response susceptibility factors include the finding that certain ethnic groups are predisposed to the pulmonary manifestations of the disease. As in the case of ABA a useful diagnostic finding is the markedly elevated serum IgE level found in this disease (Ezeoke, Perera & Hobbs, 1973). Indeed an understanding of the importance of anti-filaria IgE antibody and the high levels noted in this disease in only a minority of subjects infected may ultimately help in defining the "normal' function of IgE antibodies. Certain forms of pulmonary vasculitis such as polyarteritis nodosa and allergic granulomatous antiitis may also be associated with asthma and pulmonary eosinophilia. The recent demonstration of hepatitis B surface antigen (Sergent et al., 1976) together with immunoglobulins in involved vessel walls in polyarteritis has strongly suggested an 'immune complex' pathogenesis in at least some of the cases studied. An approximate 18% frequency of bronchial asthma has been reported in a study of 300 cases of polyarteritis nodosa and intense peripheral blood eosinophilias is present in approximately 95% of these patients (Wilson & Alexander, 1945). Thus, the pathogenesis of pulmonary manifestations of this disease may in some respect be similar to that of ABA. Pulmonary fibrosis There is increasing evidence that an immune pathogenesis may be operative in the production of many forms of pulmonary fibrosis. It is well known that diffuse fibrosis may occur in association with autoallergic or diffuse connective tissue diseases, or may develop from exposure to certain industrial agents, as an end result of pulmonary infections, or as a manifestation of certain well defined pulmonary diseases of unknown aetiology. In this discussion I shall briefiy focus only on idiopathic fibrosing alveoiitis plus those forms of pulmonary fibrosis associated with connective tissue and occupational diseases (see Table 2). Pulmonary fibrosis associated with connective tissue diseases In autoallergic connective tissue diseases such as systemic lupus erythematosus the lungs are clinically involved in 50 to 70% of cases, and where an autopsy is performed up to a 98% frequency of interstitial pneumonitis and a 70% incidence of interstitial fibrosis have been reported. The intriguing possibility that anti-double stranded DNA antibody or other anti-nuclear antibody in the form of immune complexes may play a
Table 2. Etiology of Pulmonary Fibrosis
Connective tissue diseases
Occupational diseases
Infectious diseases
Idiopathic diseases
Systemic Lupus erythematosis Progressive systemic sclerosis Rheumatoid arthritis Polymositis Goodpasture's syndrome Idiopathic fibrosing alveoiitis
Silicosis Berylliosis Asbestosis Hypersensitivity pneumonitis Pharmaceutical reactions
Tuberculosis Coccidioidomycosis Histoplasmosis Cryptococcosis Helminths Viruses?
Eosinophilic granuloma Sarcoidosis Alveolar proteinosis Alveolar microlithiasis Pulmonary hemosiderosis Neoplasm
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central role in development of these lung lesions is being supported by increasing data from several animal models. For example, Brentjens and co-workers have demonstrated that rabbits hyperimmunized to bovine serum albumin by i.v. injection of daily large quanties of antigen so as to maintain the animals in a state of relative antigen antibody equivalence, developed membranous and/or proliferative lesions in the lung, associated with tissue deposition of antigen, host immunoglobulin, complement and fibrinogen (Brentjens et al., 1974). Dreisen and co-workers in studying diffuse idiopathic pulmonary fibrosis have also demonstrated circulating immune complexes in the serum of many patients exhibiting the early cellular phase of the disease (Dreisin et al., 1978). In Goodpasture's syndrome hemorrhagic pneumonia with subsequent nephritis usually occurs in young males and commonly results in death from renal failure, hypertension and massive hemoptysis. Renal biopsies demonstrate a proliferative glomerulitis with epithelial cresents. igG, plus complement components have also been classically demonstrated by fluorescent staining in a linear deposition along glomerular basement membrane and IgG has, by passive transfer experiments shown to be anti-glomerular basement membrane antibody (Dixon, 1971). It has long been suspected that there is a close relationship between the pulmonary and renal manifestations of this disease. Indeed, immunofiuorescence studies have demonstrated antiGBM antibody in the lung (Beirne et al., 1968), although this finding has been disputed by others. At present the exact relationship between the hemorrhagic pneumonitis and nephritis remains uncertain, but an immunologic event linking lesions in both organs as well as in immune pathogenesis for the disease seems likely. Idiopathie fibrosing alveoiitis Evidence is accumulating which suggests a common underlying immunological abberation in this large group of patients with diffuse interstitial pulmonary fibrosis in which no underlying occupational exposure, connective tissue disease, or other aetioiogical factors are apparent. Immunoglobulin and complement have been demonstrated in the lungs of patients with this disease. Autoantibodies such as rheumatoid factors and antinuclear antibodies are known to occur in the sera in over 50% of cases (Haslam, Turner-Warwick & Lukoszek, 1975) and over 95% of the patients with this disease have been shown to produce lymphokines such as MIF in vitro in response to type I collagen (Crystal et ai., 1976). Of interest has also been a recent finding of high levels of circulating immune complexes in the majority of patients exhibiting the more cellular phase of this disease. Many of these patients, also ultimately develop other autoallergic connective tissue diseases (Dreisin et al., 1978). Occupational fibrotic diseases In silicosis, the most common of the pneumoconiosis, which results from repeated inhalation of free crystalline silicon dioxide, there is evidence that immune factors might be operative in perpetuating fibrosis or accelerating the disease, particularly the common chronic type which develops in cigarette smokers after long-term silica dust exposure. There have been reports of a high prevalence of non-organ specific antinuclear autoantibodies, in patients with silicosis (Jones et al., 1977). The association between nodular lung fibrosis on chest X-ray and rheumatoid arthritis in pneumoconiotic coal miners (Caplan's syndrome), also vaguely suggests an immune process as does the high
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incidence of autoallergic connective tissue diseases in patients with silicosis. The possible role of inhaled silica in the formation of rheumatoid factor and immune complexes, plus their relationship to intestitial lung diseases remains unknown however, and is currently under investigation in several laboratories. In view of the established cytotoxicity of silica for macrophages, their prominent participation as effector cells in delayed hypersensitivity, and the known high incidence of tuberculosis in silicosis, one might suspect an abnormality of delayed hypersensitivity in this disease. Immunocompetence skin test studies for delayed hypersensitivity, peripheral T- and B-cell quantitation, and lymphocyte transformation with pokeweed mitogen and PHA in patients with silicosis have, however, all yielded results comparable to these noted in control groups. However, lymphocyte transformation with low doses of concanavalin A is diminished in patients with silicosis and impaired MIF production following stimulation with certain antigens has been reported (Schuyler, Ziskind & Salvaggio, 1977). In view of these findings, a continued search for defects in T-cell function might conceivably provide further clues to the complex interrelationship between silica, autoantibodies, immune complexes, interstitial pulmonary fibrosis and possibly regulatory suppressor cell activity In berylliosis, evidence is accumulating that in the chronic granulomatous form of this disease delayed hypersensitivity to beryllium salts likely acting as haptens is operative in disease pathogenesis. Indeed in vitro MIF production as well as delayed dermal skin reactivity have been demonstrated in both sensitized guinea pigs and in man with beryllium salts. Hypersensitivity has also been transferred with sensitized lymphoid cells in some species and more recently with transfer factor in man (Marx & Burrell, 1973). In spite of induction of MIF production, beryllium salts evidently suppress lymphocyte transformation in the guinea pig and rabbit indicating an inhibitory effect on DNA synthesis (Jones & Amos, 1975). At this time, it seems likely that beryllium salts possess toxic as well as immunogenic properties, both of which are operative in the pathogenesis of chronic granulomatous pulmonary lesions. In asbestosis, symptoms may not develop until 7 to 10 years following onset of exposure. Dry cough and exertional dyspnea, plus a diffuse non-nodular interstitial infiltrate prominent at the lung bases is often seen. Characteristically ferruginous bodies 20 to 50 /im (asbestos fibres coated with ferritin containing proteins) imbedded in a meshwork of interstitial and alveolar fibrosis is noted. As in the case of silicosis, immunologic events may be partially responsible for disease pathogenesis. It is known that asbestos fibres for example, can induce release of lysosomal enzymes from alveolar macrophages in vitro and these fibres may also be cytolytic (Allison, 1971). Unlike silica, asbestos fibres have been reported to activate the alternate pathway of complement and to generate chemotactic factors as well as induce a biochemiluminescence in peripheral blood neutrophils (Wilson, Gaumer & Salvaggio, 1977), Factors which might be important in the disease pathogenesis. In addition, a four-fold increase in prevalence of antinuclear antibodies and theumatoid factors has been noted in patients with asbestosis and an increased prevalence in HLA-B27 haplotype has been demonstrated Turner-Warwick & Parkes, 1970. Based on these findings. Turner-Warwick & Parkes have proposed that antinuclear antibodies in asbestosis, as in silicosis, may act as accelerators of tissue injury once fibrosis has been initiated by the inorganic agent per se. The above examples represent only a portion of the ever increasing number of 'non-IgE mediated' interstitial and alveolar filling pulmonary diseases in which immunologic factors likely play a role in disease pathogenesis.
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It is only through continued development of animal models, plus application of immunological techniques in clinical studies, that the pathogenesis and ultimately the rationale for prevention and therapy of those diseases, can be fully understood.
References ALLEN. D.H.. BASTEN. A.. WILLIAMS. G . V . & WOOLCOCK. A.J. (1975) Familial hypersensitivity pneumonitis.
American Jouriuil of Medicine. 59. 505. ALLISON. A.C. (1971) EfTects of silica and asbestos on cells in culture. In: Inhaied Partides. iii (ed. W. H. Walton), p. 437. Unwin Bros. Ltd.. Gresham Press. England. BARROWCLIFF. D.F. & ARBLASTER. P.G. (1968) Farmer's lung: A study of an early fatal case. Thorax 23:490. BEIRNE. G.J.. OCTAVIANO. G.N.. KOOP. W . L . & BURNS. R.O. (1968) Immunohistology of the lung in
Goodpasture's syndrome. Annais of Internai Medicine. 69. 1207. BICE. D.E.. MCCARRON. K . . HOFFMAN. E.O. & SALVAGGIO. J.E. (1977) Adjuvant properties of Macropoiv-
.spora faeni. Internationai Archives of Aiiergy and Appiied Immunology, 55. 267. BICE. D.E.. SALVAGGIO. J.E. & HOFFMAN. E. (1976) Passive transfer of experimental hypersensitivity pneumonitis with lymphoid cells in the rabbit. Journai of Aiiergy and Ciinicai Immunoiogv. 58. 250. BRENTJENS. J R . . O'CONNELL. D.W.. PAWLOWSKI. I B . . Hsu. K.C. & ANDRES. G.A. (1974) Experimental
immune complex disease of the lung. Journal of E.xperimentai Medicine. 140. 105. CRYSTAL. R.G.. FULMER. J.D.. ROBERTS. W.C.. Moss. M.L.. LINE. B . R . & REYNOLDS. H . Y . (1976) Idiopathic
pulmonary fibrosis. Annais of Internai Medicine, 85. 769. DIXON. F.J. (l971)Glomerulonephritisand Immunopathology. In: Immunobioiogy {eds R. A. Good and D. W. Fisher), p. 167. Sinauer Associates. Inc.. Stanford. Connecticut. DREISIN. R.. SCHWARZ. M . THEOFILOPOULOS. A. & STANFORD. R. (1978) Circulating immune complexes in
the idiopathic interstitial pneumonias. New Engiand Journal of Medicine. 298. 353. EDWARDS. J.H.. BAKER. J.T. & DAVIES. B.H. (1974) Precipitin test negative farmers' lung—activation of the alternative pathway of complement by mouldy hay dust. Ciinicai Aiiergy. 4. 379. EZEOKE. A.. PERERA. A.B.V. & HOBBS. J.R. (1973) Serum IgE elevation with tropical eosinophilia. Ciinicai Aiiergy. 3, i:i. FLAHERTY. D.K.. IHA. T.. CHEMLIK. F.. DICKIE. H . & REED. C.E. (1975) HLA-8 and farmers' lung disease. Lancet, ii. 507. GERMUTH. F.G. (1961) The biologic significance of experimentally induced allergic granulomas. American Review of Respiratory Dl.sea.'ies. (Suppl) 84. 84. GHOSE. T . . LANDRIGAN. P., KILLEEN. R. & DILL. J. (1974) Immunopathological studies in patients with farmers' lung. Clinical Allergy. 4. 119. GoLBERT. T.M. & PATTERSON. R. (1970) Pulmonary allergic aspergillosis. Annais of Internal Medicine 72 395. HARGREAVE. F.E. & PEPYS. J. (1972) Allergic respiratory reactions in bird fanciers provoked by allergen inhalation provocation tests. Journal of Aiiergy and Ciinicai Immunoiogy. 50. 157. HARRIS. J.O.. BICE. D . & SALVAGGIO. J.E. (1976) Cellular and humoral bronchopulmonary immune response of rabbits immunized with thermophilic actinomycetes antigen. American Review of Respiratory Diseases. 114. 29. HASLAM. P.. TURNER-WARWICK. M . & LUKOSZEK. A. (1975) Antinuclear antibody and lymphocyte responses to nuclear antigens in patients with lung disease. Ciinicai and E.xperimentai Immunoiogy, 20, 379. HINSON. K.F.W., MOON. A.J. & PLUMMER. N.S. (1952) Bronchopulmonary aspergillosis. Thorax. 7. 317. JONES. J.M. & AMOS. H E . (1975) Contact sensitivity in vitro. II. The effect of beryllium preparations on the proliferative responses of specifically allergized lymphocytes and normal lymphocytes stimulated with PHA. Internationai Archives of Aiiergy and Applied Immunoiogy. 48. 22. JONES. R.N.. TURNER-WARWICK. M . . ZISKIND. M . & WEILL. H . (1977) High prevalence of antinuclear
antibodies in sandblaster's silicosis. American Review of Respiratory Diseases. 113, 393. MARX, J.J. & BURRELL. R. (1973) Delayed hypersensitivity to beryllium compounds. Journai of Immunoiogy. 111.590. MCCARTHY. D.S. & PEPYS, J. (1971a) Allergic bronchopulmonary aspergillosis. Clinical immunology: (1) Clinical features. Ciinicai Aiiergy. 1, 261.
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MCCARTHY, D.S. & PEPYS. J. (1971b) Allergic bronchopulmonary aspergillosis. Clinical immunology: (2) Skin, nasal, and bronchial tests. Ciinicai Allergy. 1, 415. M
Immunological mechanisms in pulmonary diseases
J. E. SALVAGGIO Tulane University, Department of Medicine, New Orleans, U.S.A. (Received 1 June 1979: accepted 7 June 1979)
Although the subject of this symposium, IgE and Mechanisms in Immediate Hypersensitivity, is applicable to most of the common atopic respiratory diseases, there are many other respiratory diseases that are not necessarily IgE mediated. In this talk I shall briefiy touch on the immunological mechanisms involved in the pathogenesis of some of these diseases including allergic alveoiitis (hypersensitivity pneumonitis), the eosinophilic pneumonias and pulmonary fibrosis associated with certain connective tissue, inorganic dust, and occupational diseases. Allergic alveoiitis I should like to limit this term to include those alveolar filling and interstitial pulmonary diseases that result from prolonged exposure to large quantities of finely disbursed organic dusts (of animal protein, actinomycete or fungal origin). These diseases are generally characterized by several common features which include the following: (1) Histologically they are composed primarily of mononuclear cell interstitial and alveolar infiltrates; (2) they involve primarily peripheral airways (alveoli and interstitial tissue); (3) granuloma formation is often a prominent histological feature; (4) systemic involvement as often noted in other granulomatous interstitial pulmonary diseases such as sarcoidosis is not present; (5) they are uniformly associated with serum precipitating antibodies against the appropriate offending organic dust; (6) in vitro correlates of cell mediated or delayed hypersensitivity indicative of lymphokine production are usually positive in symptomatic patients; (7) the diseases are associated with elevated serum levels of IgG, A and M, but IgE levels are usually normal and there is no eosinophilia; (8) large numbers of alveolar cells with the characteristics of activated macrophages are characteristically found within the pulmonary lesions. Many significant recent advances in our knowledge of this disease entity have been made in the area of pathogenesis. The antigens involved have been shown to exert several important biological effects. These include: (1) non-specific activation of the alternative pathway of complement and of alveolar macrophages; (2) a non-specific Correspondence: Dr J. E. Salvaggio, Tulane University, Department of Medicine, Clinical Immunology Section, 1700 Perdido Street, New Orleans, LA 70112, U.S.A. 0009-9090/79/HOO-0659$02.00
© 1979 Blackwell Scientific Publications.
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adjuvant and mitogenic effect; (3) a specific humoral and cellular immune response (serum antibody and lymphokine production); (4) potential to induce tissue destruction (macrophage lysosomal enzyme release). Factors which predispose toward development of this disease are poorly understood. The prevalence of atopic disease is not increased and serum IgE levels and eosinophil counts are typically normal. There is, however, evidence for a possible genetically determined susceptibility. HLA-BW40 has been found with increased frequency in pigeon breeders' disease Allen et al., 1975; Flaherty et al., 1975; Rittner, Sennekamp & Vogel, 1975). Since these antigens are closely linked to immune responses (IR) genes in the major histocompatibility complex, the increased frequency of the B. locus may suggest the presence of an IR gene governing abnormal reactivity to some of the offending aetioiogical organic dusts. Some of the aetioiogical agents in allergic alveoiitis can induce non-specific pulmonary inflammation via activation of the alternative complement pathway or a non-specific adjuvant effect (Bice et al., 1977; Edwards, Baker & Davies, 1974). It has also been determined that induction of prior inflammation of the lung with agents such as BCG, followed by challenge with organic dust or animal protein antigens can induce granulomatous pulmonary lesions resembling those of allergic alveoiitis in association with demonstrable 'local' pulmonary cell mediated hypersensitivity. If these same antigens are administered in a non-particulate form or without prior induction of pulmonary infiammation, lesions are not produced (Moore, Heasley & Fink, 1975). Studies in man and animal models have contributed greatly to our understanding of specific immune responses to aetioiogical antigens in allergic alveoiitis. Although IgE mediated hypersensitivity appears to be of little importance in classical granulomatous allergic alveoiitis, many patients with certain forms of this disease such as pigeon breeders' or bird fanciers' lung demonstrate immediate weal and fiare skin reactions to crude avian antigens. Occasional immediate type asthmatic responses have also occurred following bronchoprovocation challenge testing with these antigens. There is also indirect evidence that cytotoxic (type II) allergic tissue injury may be operative in disease pathogenesis based on demonstration of actinomycete antigen, immunoglobulin and complement components in bronchial walls and on the surface of alveolar macrophages in lung biopsy specimens from patients with farmers' lung (Wenzel, Emmanuel & Gray, 1971). According to this hypothesis soluble inhaled antigen absorbed onto alveolar macrophages and bronchial lining cells would produce direct complement-dependent cell injury at the alveolar interstitial and bronchial level in the presence of specific antibody. Evidence for immune complexes being operative in the pathogenesis of this disease is considerably stronger and has traditionally represented the conventional wisdom in discussing pathogenesis of this disease. IgG precipitating antibody specific for the offending organic dust is present in the serum of patients with the disease and its presence often correlates with intensity of exposure. In the case of some antigens, skin testing induces both early weal and fiare and late (4 to 8 h) Arthus type reactions characterized by necrotizing vasculitis, deposition of complement and immunoglobulin in vessel walls (Pepys, 1969). Symptoms that occur following bronchoprovocation challenge testing also develop after a 4 or 8 hr latent period in many cases closely paralleling the time course observed with the Arthus reaction. In addition, some early lung biopsy specimens obtained from patients with the disease have revealed the presence of antigen, immunoglobulins, and complement deposition by immunofiuor-
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escence as well as necrotizing vasculitis (Ghose et al., 1974; Barrowcliff & Arblaster, 19.68). Interpretation of the above data is controversial, however, since precipitins are present in a large percentage of exposed but asymptomatic subjects and the mononuclear cell and granulomatous infiltrates seen in most cases of allergic alveoiitis are substantially different from the vasculitis lesions seen in other immune complex diseases of man. It is, however, possible that immune complexes can activate alveolar macrophages to secrete hydrolytic enzymes and it is known that insoluble antigen antibody complexes not readily digested by lysospmal enzymes may lead to granuloma formation (Germuth, 1961; Hargreave & Pepys, 1972). Many recent animal models have focused on defining the possible contribution of cell mediated or type IV hypersensitivity in the pathogenesis of this disease since the pulmonary histopathology greatly resembles that of cell mediated hypersensitivity reactions. Studies in man have demonstrated that lymphokine production occurs after peripheral blood or bronchoalveolar lymphocytes are exposed to both avian and/or actinomycete antigens and in some forms of allergic alveoiitis lymphokine production appears to correlate with disease activity. Several animal models of the disease have also clearly demonstrated lymphokine production at the bronchoalveolar level (Salvaggio et al., 1975). In addition, pulmonary lesions resembling those seen in the human disease have been produced after transfer of specifically sensitized lymph node cells followed by aerosol or intratracheal challenge with appropriate antigen (Bice, Salvaggio & Hoffman, 1976). Such lesions have generally not been successfully transfered with hyperimmune serum. Since it is apparent that local, organ restricted, immune mechanisms may be operative at the pulmonary level with or without systemic manifestations of sensitization, studies of bronchoalveolar lavage specimens and cells in animal models of allergic alveoiitis and in some human cases have been undertaken. Reynolds and co-workers noted a higher proportion of lymphocytes, higher IgE and IgM levels and higher T/B cell ratios in patients with allergic alveoiitis when compared with control subjects (Reynolds et al., 1977). In other studies of allergic alveoiitis in man, lymphokine production has been demonstrated by bronchoalveolar cells while peripheral cells failed to demonstrate reactivity to the same antigen (Schuyler, Thigpen & Salvaggio, 1978). Attempts to have been made to correlate development of alveoiitis lesions with immunological events in other animal models. In one study of this type, repeated respiratory tract exposure of rabbits to actinomycete antigen has lead to the development of pulmonary lesions compatable with those of human allergic alveoiitis. The early lesions were composed predominantly of interstitial, peribronchial and intraalveolar mononuclear cells and the later lesions characterized by granuloma and giant cell formation, with most animals demonstrating complete resolution of lesions by 21 to 30 days. In these animals lavage studies indicated a striking increase in number of bronchoalveolar cells after intratracheal installation of particulate actinomycete antigen. Many of these cells demonstrated the morphology of immature or young macrophages containing few phagolysosomes, suggesting that they were recruited in response to lung injury. Alveolar macrophages in this model also showed evidence of 'activation' morphologically, metabolically and with regard to phagocytic and bactericidal activity (Harris, Bice & Salvaggrio, 1976). Following spontaneous regression of pulmonary infiltrates, both pulmonary granulomatous lesions and the state of macrophage activation could also be specifically 'recalled' by challenge with actinomycete antigen via the respiratory tract route.
662 J. E. Salvaggio Since most organic dusts are efiicient activators of the alternative complement pathway, it may be that formation of complement split products such as C3B which are known to induce macrophage lysosomal enzyme release might explain some of the early non-specific lesions of allergic alveoiitis. Since lysosomal enzymes can in turn cleave further C3, a mechanism for continued macrophage activation via an 'amplification loop' process is operative and it is conceivable that pulmonary granulomas containing macrophages with ingested organic dust antigen may evolve in part through this type mechanism. Indeed, Schorlemmer and associates have formulated an hypothesis for the development of allergic alveoiitis that postulates the initial activation of complement by inhaled organic dust antigen with subsequent generation of chemotactic factors and the operation of such an 'amplification loop' resulting in non-specific inflammation (Schorlemmer et al., 1977). In addition, we would propose other immunologically specific mechanisms that could equally account for granuloma formation involving sensitized bronchoalveolar B and T cells. For example, the formation of local immune complexes, which have been demonstrated in animal models of this disease, could lead to activation of alveolar macrophages following ingestion, or could directly induce granuloma formation as has been shown long ago by Germuth (1961). Spector & Heesom (1969). Additionally, sensitized bronchoalveolar T cells which are known to secrete lymphokines in animal models of this disease might participate and produce further lymphokine induced macrophage activation. In any event, the pathogenetic focal point of this hypothesis would be the activated alveolar macrophage which would serve as a functional link between the inhaled offending organic dust antigen and the subsequent mononuclear cell and granulomatous pulmonary lesions. Thus, according to this hypothesis through immunologically specific as well as non-specific processes involving locally formed immune complexes, lymphokine production, and alternative pathway complement activation, pulmonary inflammation would persist as long as antigen is present. According to this hypothesis it would also be possible that persistent inflammation could result in fibrosis via a macrophage mediated influence on fibroblasts by soluble mediators. Eosinophilie pneumonias If one adapts the term eosinophilic pneumonias to include all lung diseases characterized by roentgenographic evidence of pulmonary infiltrates accompanied by either peripheral blood eosinophilia or eosinophilic infiltrative lung disease, one might conveniently divide these diseases into asthmatic and non-asthmatic varieties as illustrated in Table 1. This classification presupposes the importance of host airways lability as a susceptibility factor despite the occasional exception. The classification accounts for major conceptual differences in the eosinophilic penumonias and can be useful in understanding disease mechanisms. Little new information is available on the pathogenesis of the eosinophilic pneumonias with the exception of the asthmatic varieties particularly allergic bronchopulmonary aspergillosis (ABA) (Hinson, Moon & Plummer, 1952) and even this disease is still defined in nebulous terms. This disease has been extensively reviewed and in this summary we will concentrate only briefly on pathogenesis which may serve as a model for some of the other eosinophilic pneumonias when appropriate antigens have been identified. Unlike allergic alveoiitis there have been few animal models of this disease. In studies of man, however, employing crude extracts of mat and spores from Asper-
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Table 1. Eosinophilic pneumonias
Asthmatic
Non-asthmatic
1. Allergic bronchopulmonary aspergillosis
Infection and infestation (Loeffler's Syndrome and chronic eosinophilic pneumonia Drugs and chemicals Eosinophilic granuloma of lung
2. Tropical eosinophilia 3. Pulmonary vasculitis (Polyarteritis nodosa and allergic granulomatous angiilis) 4. —
Leukocytic neoplasms
gillus cultures as antigen, characteristic positive skin responses consisting of an immediate weal and flare reaction followed by a late (4 to 8 hr) reaction have been noted. In a study of twenty subjects with ABA all demonstrated an immediate weal and flare reaction and 33% demonstrated the late reaction (Rosenberg et al., 1977). The detection of serum precipitating antibody against A. fumigatus antigen by simple Ouchterlony gel diffusion is also characteristic of ABA in over 50% of the cases. Anti-Aspergillus antibodies can, however, be detected in the sera of many normal individuals .when sensitive primary binding assays are used, suggesting that the population-atlarge have anti-fungal antibody as a reflection of environmental exposure to ubiquitous fungal antigens. In addition, patients with ABA have marked peripheral blood and sputum eosinophilia and elevated total serum IgE antibody levels (Patterson & Roberts, 1974) which parallel diseases activity. In spite of high IgE levels, however, the amount of specific IgE antibody directed against A. fumigatus is not always extremely elevated. It is well known, based on experimental evidence in the rabbit, that antigen induced IgE mediated release of histamine can facilitate egress of circulating immune complexes into vascular walls and tissues with resultant production of infiammation through activation of the classical complement pathway and such a mechanism has been thought to be operative in production of lesions in allergic bronchopulmonary aspergillosis. Alternatively, intense IgE immediate reactions might result in accumulations of tissue eosinophils via the release of mediators such as eosinophilic chemotactic factor of anaphylaxis (ECFA) as has been proposed for late 'IgE dependent' reactions in general. The existence of either of these mechanisms in ABA is supported by the clinical observations that disodium cromoglycate, a known inhibitor of IgE mediated release of histamine can block both the immediate and late asthmatic reactions following bronchoprovocation challenge testing in these patients (McCarthy & Pepys, 1971, a, b). In addition it has been shown in passive transfer studies involving primates that infusion of serum containing both precipitating and reaginic antibody followed by challenge leads to pulmonary lesions compatible with those of ABA, whereas the administration of serum rich in reagins only, without precipitins, fails to transfer lesions upon challenge (Goibert & Patterson, 1970). In spite of the evidence for an exclusive humoral mechanism in this disease, other data indicate the presence of antigen induced lymphocyte transformation to Aspergillus antigen in symptomatic patients and not in control subjects. The interpretation of these data is unclear at present. The pathogenesis of other eosinophilic pneumonias is even more uncertain than that of ABA. In tropical eosinophilia the hypothesis that the disease results from an
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immunological host response that facilitates entrapment of microfilaria in tissues and precludes their circulation in the blood is favoured. In this disease, support for host response susceptibility factors include the finding that certain ethnic groups are predisposed to the pulmonary manifestations of the disease. As in the case of ABA a useful diagnostic finding is the markedly elevated serum IgE level found in this disease (Ezeoke, Perera & Hobbs, 1973). Indeed an understanding of the importance of anti-filaria IgE antibody and the high levels noted in this disease in only a minority of subjects infected may ultimately help in defining the "normal' function of IgE antibodies. Certain forms of pulmonary vasculitis such as polyarteritis nodosa and allergic granulomatous antiitis may also be associated with asthma and pulmonary eosinophilia. The recent demonstration of hepatitis B surface antigen (Sergent et al., 1976) together with immunoglobulins in involved vessel walls in polyarteritis has strongly suggested an 'immune complex' pathogenesis in at least some of the cases studied. An approximate 18% frequency of bronchial asthma has been reported in a study of 300 cases of polyarteritis nodosa and intense peripheral blood eosinophilias is present in approximately 95% of these patients (Wilson & Alexander, 1945). Thus, the pathogenesis of pulmonary manifestations of this disease may in some respect be similar to that of ABA. Pulmonary fibrosis There is increasing evidence that an immune pathogenesis may be operative in the production of many forms of pulmonary fibrosis. It is well known that diffuse fibrosis may occur in association with autoallergic or diffuse connective tissue diseases, or may develop from exposure to certain industrial agents, as an end result of pulmonary infections, or as a manifestation of certain well defined pulmonary diseases of unknown aetiology. In this discussion I shall briefiy focus only on idiopathic fibrosing alveoiitis plus those forms of pulmonary fibrosis associated with connective tissue and occupational diseases (see Table 2). Pulmonary fibrosis associated with connective tissue diseases In autoallergic connective tissue diseases such as systemic lupus erythematosus the lungs are clinically involved in 50 to 70% of cases, and where an autopsy is performed up to a 98% frequency of interstitial pneumonitis and a 70% incidence of interstitial fibrosis have been reported. The intriguing possibility that anti-double stranded DNA antibody or other anti-nuclear antibody in the form of immune complexes may play a
Table 2. Etiology of Pulmonary Fibrosis
Connective tissue diseases
Occupational diseases
Infectious diseases
Idiopathic diseases
Systemic Lupus erythematosis Progressive systemic sclerosis Rheumatoid arthritis Polymositis Goodpasture's syndrome Idiopathic fibrosing alveoiitis
Silicosis Berylliosis Asbestosis Hypersensitivity pneumonitis Pharmaceutical reactions
Tuberculosis Coccidioidomycosis Histoplasmosis Cryptococcosis Helminths Viruses?
Eosinophilic granuloma Sarcoidosis Alveolar proteinosis Alveolar microlithiasis Pulmonary hemosiderosis Neoplasm
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665
central role in development of these lung lesions is being supported by increasing data from several animal models. For example, Brentjens and co-workers have demonstrated that rabbits hyperimmunized to bovine serum albumin by i.v. injection of daily large quanties of antigen so as to maintain the animals in a state of relative antigen antibody equivalence, developed membranous and/or proliferative lesions in the lung, associated with tissue deposition of antigen, host immunoglobulin, complement and fibrinogen (Brentjens et al., 1974). Dreisen and co-workers in studying diffuse idiopathic pulmonary fibrosis have also demonstrated circulating immune complexes in the serum of many patients exhibiting the early cellular phase of the disease (Dreisin et al., 1978). In Goodpasture's syndrome hemorrhagic pneumonia with subsequent nephritis usually occurs in young males and commonly results in death from renal failure, hypertension and massive hemoptysis. Renal biopsies demonstrate a proliferative glomerulitis with epithelial cresents. igG, plus complement components have also been classically demonstrated by fluorescent staining in a linear deposition along glomerular basement membrane and IgG has, by passive transfer experiments shown to be anti-glomerular basement membrane antibody (Dixon, 1971). It has long been suspected that there is a close relationship between the pulmonary and renal manifestations of this disease. Indeed, immunofiuorescence studies have demonstrated antiGBM antibody in the lung (Beirne et al., 1968), although this finding has been disputed by others. At present the exact relationship between the hemorrhagic pneumonitis and nephritis remains uncertain, but an immunologic event linking lesions in both organs as well as in immune pathogenesis for the disease seems likely. Idiopathie fibrosing alveoiitis Evidence is accumulating which suggests a common underlying immunological abberation in this large group of patients with diffuse interstitial pulmonary fibrosis in which no underlying occupational exposure, connective tissue disease, or other aetioiogical factors are apparent. Immunoglobulin and complement have been demonstrated in the lungs of patients with this disease. Autoantibodies such as rheumatoid factors and antinuclear antibodies are known to occur in the sera in over 50% of cases (Haslam, Turner-Warwick & Lukoszek, 1975) and over 95% of the patients with this disease have been shown to produce lymphokines such as MIF in vitro in response to type I collagen (Crystal et ai., 1976). Of interest has also been a recent finding of high levels of circulating immune complexes in the majority of patients exhibiting the more cellular phase of this disease. Many of these patients, also ultimately develop other autoallergic connective tissue diseases (Dreisin et al., 1978). Occupational fibrotic diseases In silicosis, the most common of the pneumoconiosis, which results from repeated inhalation of free crystalline silicon dioxide, there is evidence that immune factors might be operative in perpetuating fibrosis or accelerating the disease, particularly the common chronic type which develops in cigarette smokers after long-term silica dust exposure. There have been reports of a high prevalence of non-organ specific antinuclear autoantibodies, in patients with silicosis (Jones et al., 1977). The association between nodular lung fibrosis on chest X-ray and rheumatoid arthritis in pneumoconiotic coal miners (Caplan's syndrome), also vaguely suggests an immune process as does the high
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incidence of autoallergic connective tissue diseases in patients with silicosis. The possible role of inhaled silica in the formation of rheumatoid factor and immune complexes, plus their relationship to intestitial lung diseases remains unknown however, and is currently under investigation in several laboratories. In view of the established cytotoxicity of silica for macrophages, their prominent participation as effector cells in delayed hypersensitivity, and the known high incidence of tuberculosis in silicosis, one might suspect an abnormality of delayed hypersensitivity in this disease. Immunocompetence skin test studies for delayed hypersensitivity, peripheral T- and B-cell quantitation, and lymphocyte transformation with pokeweed mitogen and PHA in patients with silicosis have, however, all yielded results comparable to these noted in control groups. However, lymphocyte transformation with low doses of concanavalin A is diminished in patients with silicosis and impaired MIF production following stimulation with certain antigens has been reported (Schuyler, Ziskind & Salvaggio, 1977). In view of these findings, a continued search for defects in T-cell function might conceivably provide further clues to the complex interrelationship between silica, autoantibodies, immune complexes, interstitial pulmonary fibrosis and possibly regulatory suppressor cell activity In berylliosis, evidence is accumulating that in the chronic granulomatous form of this disease delayed hypersensitivity to beryllium salts likely acting as haptens is operative in disease pathogenesis. Indeed in vitro MIF production as well as delayed dermal skin reactivity have been demonstrated in both sensitized guinea pigs and in man with beryllium salts. Hypersensitivity has also been transferred with sensitized lymphoid cells in some species and more recently with transfer factor in man (Marx & Burrell, 1973). In spite of induction of MIF production, beryllium salts evidently suppress lymphocyte transformation in the guinea pig and rabbit indicating an inhibitory effect on DNA synthesis (Jones & Amos, 1975). At this time, it seems likely that beryllium salts possess toxic as well as immunogenic properties, both of which are operative in the pathogenesis of chronic granulomatous pulmonary lesions. In asbestosis, symptoms may not develop until 7 to 10 years following onset of exposure. Dry cough and exertional dyspnea, plus a diffuse non-nodular interstitial infiltrate prominent at the lung bases is often seen. Characteristically ferruginous bodies 20 to 50 /im (asbestos fibres coated with ferritin containing proteins) imbedded in a meshwork of interstitial and alveolar fibrosis is noted. As in the case of silicosis, immunologic events may be partially responsible for disease pathogenesis. It is known that asbestos fibres for example, can induce release of lysosomal enzymes from alveolar macrophages in vitro and these fibres may also be cytolytic (Allison, 1971). Unlike silica, asbestos fibres have been reported to activate the alternate pathway of complement and to generate chemotactic factors as well as induce a biochemiluminescence in peripheral blood neutrophils (Wilson, Gaumer & Salvaggio, 1977), Factors which might be important in the disease pathogenesis. In addition, a four-fold increase in prevalence of antinuclear antibodies and theumatoid factors has been noted in patients with asbestosis and an increased prevalence in HLA-B27 haplotype has been demonstrated Turner-Warwick & Parkes, 1970. Based on these findings. Turner-Warwick & Parkes have proposed that antinuclear antibodies in asbestosis, as in silicosis, may act as accelerators of tissue injury once fibrosis has been initiated by the inorganic agent per se. The above examples represent only a portion of the ever increasing number of 'non-IgE mediated' interstitial and alveolar filling pulmonary diseases in which immunologic factors likely play a role in disease pathogenesis.
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It is only through continued development of animal models, plus application of immunological techniques in clinical studies, that the pathogenesis and ultimately the rationale for prevention and therapy of those diseases, can be fully understood.
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