Res. MicrobioL 1990, 141, 765-768
© INSTITUTPASTEUR/ELSEVIER Paris 1990
IMMUNITY TO MYCOBACTERIA
S.H.E. Kaufmann Department of Medical Microbiology and Immunology, University of Ulm, Albert-Einstein-Alice 11, 7900 UIm (FRG)
Introduction. It probably kills more people in the world than any other infectious agent. It has infected approximately 1/3 of the whole world population. It is the number-one killer among infectious agents in developing countries. Even in several developed countries (e.g. FRG) it kills more people than any other reportable pathogen. Its name is Mycobacterium tuberculosis. Its fellow microbe, Mycobacterium leprae, afflicts less people. However, because of the marked deformities and the remarkable social stigma this pathogen causes, it is a major health problem as well (Kaufmann, 1989). The leprosy and tubercle bacilli are both acid-fast bacteria with the capacity to survive and replicate inside professional phagocytes (Hahn and Kaufmann, 1981). Due to this feature, these as well as other bacterial, fungal and protozoan pathogens cannot be attacked effectively by humoral immune mechanisms. Rather, T lymphocytes are instrumental for acquired resistance against such intraceUular microbes. T cells recognize their antigens indirectly; they see antigenic peptides in the context of gene products of the major histocompatibility complex (MHC). Such T cells, after interaction with infected macrophages which present microbial antigens, set into motion effector mechanisms which ultimately lead to the formation of granulomatous foci at the site of bacterial growth. There, protection is accomplished and pathologic alterations occur. In the following, the principle mechanisms underlying protection and pathogenesis are discussed.
Interleukins. It is well appreciated that interleukins from T cells are of major importance for local protection (Hahn and Kaufmann, 1981). In vitro data from experiments using bone-marrow-derived macrophages and recombinant interleukins support this notion. Thus, when bone-marrow-derived macrophages were stimulated with a variety of recombinant interleukins and afterwards infected with M. bovis, interferon-~'(IFNy) was identified as the only interleukin capable of inducing mycobacterial growth inhibition (Flesch and Kaufmann, 1987; 1990, in press). When bone-marrow-derived macrophages were first infected with M. boris and afterwards stimulated with these interleukins, IFN-~,was found to be less active. Interestingly, under these conditions, the B-cell stimulatory factors, interleukin 4 (IL-4) and interleukin 6 (IL-6) exerted antimycobacterial activities upon macrophages. This suggests that mycobacterial infection itself renders such macrophages responsive to B-cell stimulatory factors and confers some negative signal for IFN-y responsiveness.
766
S.H.E. KA UFMANN
Cytolytic T cells. Interleukins are generally thought to be primarily produced by T lymphocytes which express the CD4 molecule and recognize antigenic peptides in the context of MHC class II molecules. Class-lI-restricted CD4 T lymphocytes have a predilection for so-called exogenous antigens, i.e. antigens which are taken up by host cells and then reside in the endosomal compartment. In contrast, newly synthesized proteins, on their way through the Golgi apparatus and the endoplasmic reticulum, can associate with class ! gene products and hence stimulate CD8 T cells which are class-Irestricted. Viral proteins belong to this class of antigens. These findings are thought to be of biological relevance. Indeed, intracellular bacteria primarily reside in professional phagocytes in which antibacterial effector mechanisms can be stimulated by interleukins from CD4 T cells. In contrast, defence against viral pathogens markedly depends on the destruction of infected cells prior to virus assembly. While this concept, in principle, seems to be correct, evidence has been gathered that infections with intracellular bacteria and protozoa also activate class-I-restricted CD8 T lymphocytes (gaufmann, 1988). For example, when mice are depleted of CD4 or of CD8 T lymphocytes and afterwards infected with viable tubercle bacilli, infection is significantly exacerbated in both experimental groups (MiiUer et al., 1987). CD8 T cells have also been established from mice immunized with different intracellular pathogens including leprosy and tubercle bacilli. These T cells lyse host macrophages pulsed with the homologous agent indicating that cytolytic T cells participate in immunity to mycobacteria (Chiplunkar et al., 1986; DeLibero et al., 1988; Steinhoff and Kaufmann, 1988). We have to conclude from these data that antigens from intracellular microbes can associate with class I MHC products. At least for certain pathogens, a reasonable explanation can be given. First, recent studies have indicated that association with class I MHC products does not necessarily require neosynthesis and that the mere presence in the cytoplasmic compartment is sufficient for this presentation pathway (Moore et al., 1988). Second, pathogens like Listeria monocytogenes, M. leprae, and M. tuberculosis have the capacity to translocate from the endosomal into the cytoplasmic compartment (Leake et al., 1984; Gaillard et al., 1986). Hence, we can assume that products of microbes residing in the cytoplasmic compartment associate with MHC class I products. Gamma/delta T cells. Antigen recognition by T lymphocytes occurs via the T-cell receptor. The T-cell receptor of conventional CD4 and CD8 T cells is a disulphide-linked heterodimer composed of an alpha and a beta chain (for review, see Kaufmann and Kabelitz, 1990, in press). In the periphery of normal individuals these cells make up > 90 %. The remaining < 10 % of T cells use another type of receptor which is composed of a gamma and a delta chain. Our knowledge about these gamma/delta T cells is still limited and, in particular, little is known about their functional role, antigen specificity and genetic restriction. In 1989, however, several groups have provided evidence for a particular predilection of gamma/delta T cells for mycobacteria (Modlin et al., 1989; Janis et al., 1989; O'Brien et al., 1989; Holoshitz et al., 1989; Haregewoin et al., 1989). This raises the question as to whether gamma/delta T cells are involved in acquired resistance to tuberculosis and leprosy and as to which function they per-
IFN = interferon. IL = interleukin.
{ MHC = major histocompatibilitycomplex. t
I M M U N I T Y TO M Y C O B A C T E R I A
767
form. Recent studies show that mycobacteria-activated gamma/delta T cells, after restimulation with M. tuberculosis, produce IL-2 (Munk et aL, in press). Furthermore, mycobacteria-activated gamma/delta T cells acquire cytolytic activity against autologous targets primed with mycobacterial components (Munk et al., in press). Thus, it appears that both alpha/beta T cells and gamma/delta T cells play a role in immunity against mycobacterial pathogens and that they express a similar spectrum of functional activities. In addition to these antigen-specific T lymphocytes, non-specific killer cells seem to participate in immunity to mycobacteria. Conclusions. How do these different T-cell sets interact with each other in a mycobacteriai granuloma? Although much remains hypothetical, we can envisage the following scenario. A granuloma is formed of mononuclear phagocytes of different differentiatoin and maturation stages..At least some mycobacteria reside i n " a g e d " macrophages which are insufficiently equipped for intracellular killing. Activation of these macrophages with IFN-~,, IL-4 and IL-6 may help to confine these microbes to distinct loci hut may not always be sufficient for sterile elimination of the pathogens. In addition, blood-derived monocytes enter the lesion and these phagocytes are better equipped for killing. To facilitate optimal uptake by blood monocytes, it may be necessary to first lyse infected granulomatous macrophages. As long as the released bacteria are taken up by monocytes effectively, this event is to the benefit of the host. However, extensive lysis may allow for uncontrolled release of bacteria and, as a corollary, mycobacterial dissemination may occur. This, as well as tissue destruction caused by cytolytic T-cell mechanisms, is rather detrimental to the host. Although the scenario envisaged is highly speculative, it illustrates that the host-parasite relationship comprises a multitude of different elements which may both threaten and benefit the host. KEY-WORDS:Mycobacterium tuberculosis, Mycobacterium leprae, T lymphocyte; Protection, Pathogenesis.
Acknowledgements
I gratefullyacknowledgefinancialsupportfrom the UNDP/WorldBank/WHOspecialProgramfor Researchand Trainingin TropicalDiseases; Sonderforschungsbereich322; the German LeprosyRelief Association; the EC-lndia Scienceand TechnologyCooperationProgram; Landesschwerpunkt30; '.he A. Krupp award for young professors. Many thanks to R. Mahmoudi.
References
CHIPLUNKAR,S., DELIBERO,G. & KAUFMANN,S.H.E. (1986), Mycobacterium leprae-specific Lyt2+ T lymphocytes with cytolytic activity. Infect. lmmun., 54, 793-797. DELInERO, G., FLESCa, I. & KAUVMANN,S.H.E. (1988), Mycobacteria reactive Lyt2+ T cell lines. Europ. J. Immunol., 18, 59-66. FLeSCH,1. & KAUFMANN,S.H.E. (1987), Mycobacterial growth inhibition by interferon-y activated bone marrow macrophages and differential susceptibility among strains of Mycobacterium tuberculosis. J. ImmunoL, 138, 4408-4413. FL~SCH,I.E.A. & KAUFM^SN,S.H.E. (1990), Stimulation of anti-bacterial macrophage activities by B cell stimulatory factor 2/Interleukin 6. Infect. lmmun., 58, 269-271.
768
S.H.E. KA UFMANN
FLESCH, I.E.A. & KAUFMANN,S.H.E. (1990), Activation of tuberculostatic macrophage functions by Interferon-y, Interleukin 4 and Tumor Necrosis Factor. Infect. l m m u n , 58, 2675-2677. GAILLARD,J.L., BERCHE, P. & SANSONETTI,P. 0986), Transposon mutagenesis as a tool to study the role of hemolysin in the virulence of Listeria monocytogenes. Infect. Immu~., 52, 50-55. HAHN, H. & KAUFMANN,S.H.E. (1981), Role of cell-mediated immunity in bacterial infections. Rev. infect. Dis., 3, 1221-1250. HAREGEWOIN,A., SOMAN,G., HOM, C.R. & FINBERG,R.W. (1989), Human ~'~+ T cells respond to mycobacteriai heat-shock protein. Nature (Lond.), 340, 309-312. HOLOSHITZ, J., KONING,F., COLIGAN,J.E., DE BRUYN, J. ~g STROBES,S. (1989), Isolation of CD4-CD8- mycobacteria-reactive T-lymphocyt~ clones from rheumatoid arthritis synovial fluid. Nature (Lond.), 339, 226-229. JANm, E.M., KAUFMANN,S.H.E., SCHWARTZ,R.H. & PARDOLL,D.M. (1989), Activation of y8 T cells in the primary immune response to Mycobacterium tuberculosis. Science, 244, 713-716. KAUFMANN,S.H.E. (1988), CD8 + T lymphocytcs in intracellular microbial infections. ImmunoL Today, 9, 168-174. KAUFMANN,S.H.E. (1989), Leprosy and tuberculosis vaccine design. Trop. Med. Parasitol., 40, 251-257. KAUFMANN,S.H.E. & KABELITZ,D. (1990), Gamma/delta T lymphocytes and heat shock proreins. Curr. Top. Microbiol. Immunol. (in press). LEAKE,E.S., MVRVm,Q.N. & WmaHT, M.J. (1984), Phagosomal membranes of Mycobacterium bovis BCG-immune alveolar macrophages are resistant to disruption by Mycobacterium tuberculosis H37Rv. Infect. Immun., 45, 443-446. MODLIN, R.L., PIRMEZ,C., HOFMANN,F.M., TORIGIAN,V., UYEMURA,K., SEA, T.H., BLOOM, B.R. & BRENNER,M.B. (1989), Lymphocytes bearing antigen-specific -~8T-cell receptors accumulate in human infectious disease lesions. Nature (Lond.), 339, 544-548. MOORE, M.W., CARBONE,F.R. & BEVAN,M.J. (1988), Introduction of soluble protein into the class I pathway of antigen processing and presentation. Cell, 54, 777-785. MUNK,M.E., GATRILL,A. & KAUFMANN,S.H.E. (1990), Antigen-specific target cell lysis and interleukin-2 secretion by Mycobacterium tuberculosis activated "r/8 T cells. J. Ira. munol. (in press). MULLER, I., COBBOLD,S.P., WALDMANN,H. & KAUFMANN,S.H.E. (1987), Impaired resistance against Mycobacterium tuberculosis infection after selective in vivo depletion of L3T4 + and Lyt2 + T cells. Infect. Immun., 55, 2037-2041. O'BRJEN, R., HAPP, M.P., DALLAS,A., PALMER,E. & KUBO, R. (1989), Stiumation of a major subset of lymphocytes expressing T-cell receptor ~ by an antigen derived from Mycobacterium tuberculosis. Cell, 57, 667-674. STEINHOFF,U. & KAUFMANN,S.H.E. (1988), Specific lysis by CD8 + T cells of Sehwann cells expressing Mycobacterium leprae antigens. Europ. J. lmmunol., 18, 973-976.
© INSTITUTPASTEUR/ELSEVIER Paris 1990
IMMUNITY TO MYCOBACTERIA
S.H.E. Kaufmann Department of Medical Microbiology and Immunology, University of Ulm, Albert-Einstein-Alice 11, 7900 UIm (FRG)
Introduction. It probably kills more people in the world than any other infectious agent. It has infected approximately 1/3 of the whole world population. It is the number-one killer among infectious agents in developing countries. Even in several developed countries (e.g. FRG) it kills more people than any other reportable pathogen. Its name is Mycobacterium tuberculosis. Its fellow microbe, Mycobacterium leprae, afflicts less people. However, because of the marked deformities and the remarkable social stigma this pathogen causes, it is a major health problem as well (Kaufmann, 1989). The leprosy and tubercle bacilli are both acid-fast bacteria with the capacity to survive and replicate inside professional phagocytes (Hahn and Kaufmann, 1981). Due to this feature, these as well as other bacterial, fungal and protozoan pathogens cannot be attacked effectively by humoral immune mechanisms. Rather, T lymphocytes are instrumental for acquired resistance against such intraceUular microbes. T cells recognize their antigens indirectly; they see antigenic peptides in the context of gene products of the major histocompatibility complex (MHC). Such T cells, after interaction with infected macrophages which present microbial antigens, set into motion effector mechanisms which ultimately lead to the formation of granulomatous foci at the site of bacterial growth. There, protection is accomplished and pathologic alterations occur. In the following, the principle mechanisms underlying protection and pathogenesis are discussed.
Interleukins. It is well appreciated that interleukins from T cells are of major importance for local protection (Hahn and Kaufmann, 1981). In vitro data from experiments using bone-marrow-derived macrophages and recombinant interleukins support this notion. Thus, when bone-marrow-derived macrophages were stimulated with a variety of recombinant interleukins and afterwards infected with M. bovis, interferon-~'(IFNy) was identified as the only interleukin capable of inducing mycobacterial growth inhibition (Flesch and Kaufmann, 1987; 1990, in press). When bone-marrow-derived macrophages were first infected with M. boris and afterwards stimulated with these interleukins, IFN-~,was found to be less active. Interestingly, under these conditions, the B-cell stimulatory factors, interleukin 4 (IL-4) and interleukin 6 (IL-6) exerted antimycobacterial activities upon macrophages. This suggests that mycobacterial infection itself renders such macrophages responsive to B-cell stimulatory factors and confers some negative signal for IFN-y responsiveness.
766
S.H.E. KA UFMANN
Cytolytic T cells. Interleukins are generally thought to be primarily produced by T lymphocytes which express the CD4 molecule and recognize antigenic peptides in the context of MHC class II molecules. Class-lI-restricted CD4 T lymphocytes have a predilection for so-called exogenous antigens, i.e. antigens which are taken up by host cells and then reside in the endosomal compartment. In contrast, newly synthesized proteins, on their way through the Golgi apparatus and the endoplasmic reticulum, can associate with class ! gene products and hence stimulate CD8 T cells which are class-Irestricted. Viral proteins belong to this class of antigens. These findings are thought to be of biological relevance. Indeed, intracellular bacteria primarily reside in professional phagocytes in which antibacterial effector mechanisms can be stimulated by interleukins from CD4 T cells. In contrast, defence against viral pathogens markedly depends on the destruction of infected cells prior to virus assembly. While this concept, in principle, seems to be correct, evidence has been gathered that infections with intracellular bacteria and protozoa also activate class-I-restricted CD8 T lymphocytes (gaufmann, 1988). For example, when mice are depleted of CD4 or of CD8 T lymphocytes and afterwards infected with viable tubercle bacilli, infection is significantly exacerbated in both experimental groups (MiiUer et al., 1987). CD8 T cells have also been established from mice immunized with different intracellular pathogens including leprosy and tubercle bacilli. These T cells lyse host macrophages pulsed with the homologous agent indicating that cytolytic T cells participate in immunity to mycobacteria (Chiplunkar et al., 1986; DeLibero et al., 1988; Steinhoff and Kaufmann, 1988). We have to conclude from these data that antigens from intracellular microbes can associate with class I MHC products. At least for certain pathogens, a reasonable explanation can be given. First, recent studies have indicated that association with class I MHC products does not necessarily require neosynthesis and that the mere presence in the cytoplasmic compartment is sufficient for this presentation pathway (Moore et al., 1988). Second, pathogens like Listeria monocytogenes, M. leprae, and M. tuberculosis have the capacity to translocate from the endosomal into the cytoplasmic compartment (Leake et al., 1984; Gaillard et al., 1986). Hence, we can assume that products of microbes residing in the cytoplasmic compartment associate with MHC class I products. Gamma/delta T cells. Antigen recognition by T lymphocytes occurs via the T-cell receptor. The T-cell receptor of conventional CD4 and CD8 T cells is a disulphide-linked heterodimer composed of an alpha and a beta chain (for review, see Kaufmann and Kabelitz, 1990, in press). In the periphery of normal individuals these cells make up > 90 %. The remaining < 10 % of T cells use another type of receptor which is composed of a gamma and a delta chain. Our knowledge about these gamma/delta T cells is still limited and, in particular, little is known about their functional role, antigen specificity and genetic restriction. In 1989, however, several groups have provided evidence for a particular predilection of gamma/delta T cells for mycobacteria (Modlin et al., 1989; Janis et al., 1989; O'Brien et al., 1989; Holoshitz et al., 1989; Haregewoin et al., 1989). This raises the question as to whether gamma/delta T cells are involved in acquired resistance to tuberculosis and leprosy and as to which function they per-
IFN = interferon. IL = interleukin.
{ MHC = major histocompatibilitycomplex. t
I M M U N I T Y TO M Y C O B A C T E R I A
767
form. Recent studies show that mycobacteria-activated gamma/delta T cells, after restimulation with M. tuberculosis, produce IL-2 (Munk et aL, in press). Furthermore, mycobacteria-activated gamma/delta T cells acquire cytolytic activity against autologous targets primed with mycobacterial components (Munk et al., in press). Thus, it appears that both alpha/beta T cells and gamma/delta T cells play a role in immunity against mycobacterial pathogens and that they express a similar spectrum of functional activities. In addition to these antigen-specific T lymphocytes, non-specific killer cells seem to participate in immunity to mycobacteria. Conclusions. How do these different T-cell sets interact with each other in a mycobacteriai granuloma? Although much remains hypothetical, we can envisage the following scenario. A granuloma is formed of mononuclear phagocytes of different differentiatoin and maturation stages..At least some mycobacteria reside i n " a g e d " macrophages which are insufficiently equipped for intracellular killing. Activation of these macrophages with IFN-~,, IL-4 and IL-6 may help to confine these microbes to distinct loci hut may not always be sufficient for sterile elimination of the pathogens. In addition, blood-derived monocytes enter the lesion and these phagocytes are better equipped for killing. To facilitate optimal uptake by blood monocytes, it may be necessary to first lyse infected granulomatous macrophages. As long as the released bacteria are taken up by monocytes effectively, this event is to the benefit of the host. However, extensive lysis may allow for uncontrolled release of bacteria and, as a corollary, mycobacterial dissemination may occur. This, as well as tissue destruction caused by cytolytic T-cell mechanisms, is rather detrimental to the host. Although the scenario envisaged is highly speculative, it illustrates that the host-parasite relationship comprises a multitude of different elements which may both threaten and benefit the host. KEY-WORDS:Mycobacterium tuberculosis, Mycobacterium leprae, T lymphocyte; Protection, Pathogenesis.
Acknowledgements
I gratefullyacknowledgefinancialsupportfrom the UNDP/WorldBank/WHOspecialProgramfor Researchand Trainingin TropicalDiseases; Sonderforschungsbereich322; the German LeprosyRelief Association; the EC-lndia Scienceand TechnologyCooperationProgram; Landesschwerpunkt30; '.he A. Krupp award for young professors. Many thanks to R. Mahmoudi.
References
CHIPLUNKAR,S., DELIBERO,G. & KAUFMANN,S.H.E. (1986), Mycobacterium leprae-specific Lyt2+ T lymphocytes with cytolytic activity. Infect. lmmun., 54, 793-797. DELInERO, G., FLESCa, I. & KAUVMANN,S.H.E. (1988), Mycobacteria reactive Lyt2+ T cell lines. Europ. J. Immunol., 18, 59-66. FLeSCH,1. & KAUFMANN,S.H.E. (1987), Mycobacterial growth inhibition by interferon-y activated bone marrow macrophages and differential susceptibility among strains of Mycobacterium tuberculosis. J. ImmunoL, 138, 4408-4413. FL~SCH,I.E.A. & KAUFM^SN,S.H.E. (1990), Stimulation of anti-bacterial macrophage activities by B cell stimulatory factor 2/Interleukin 6. Infect. lmmun., 58, 269-271.
768
S.H.E. KA UFMANN
FLESCH, I.E.A. & KAUFMANN,S.H.E. (1990), Activation of tuberculostatic macrophage functions by Interferon-y, Interleukin 4 and Tumor Necrosis Factor. Infect. l m m u n , 58, 2675-2677. GAILLARD,J.L., BERCHE, P. & SANSONETTI,P. 0986), Transposon mutagenesis as a tool to study the role of hemolysin in the virulence of Listeria monocytogenes. Infect. Immu~., 52, 50-55. HAHN, H. & KAUFMANN,S.H.E. (1981), Role of cell-mediated immunity in bacterial infections. Rev. infect. Dis., 3, 1221-1250. HAREGEWOIN,A., SOMAN,G., HOM, C.R. & FINBERG,R.W. (1989), Human ~'~+ T cells respond to mycobacteriai heat-shock protein. Nature (Lond.), 340, 309-312. HOLOSHITZ, J., KONING,F., COLIGAN,J.E., DE BRUYN, J. ~g STROBES,S. (1989), Isolation of CD4-CD8- mycobacteria-reactive T-lymphocyt~ clones from rheumatoid arthritis synovial fluid. Nature (Lond.), 339, 226-229. JANm, E.M., KAUFMANN,S.H.E., SCHWARTZ,R.H. & PARDOLL,D.M. (1989), Activation of y8 T cells in the primary immune response to Mycobacterium tuberculosis. Science, 244, 713-716. KAUFMANN,S.H.E. (1988), CD8 + T lymphocytcs in intracellular microbial infections. ImmunoL Today, 9, 168-174. KAUFMANN,S.H.E. (1989), Leprosy and tuberculosis vaccine design. Trop. Med. Parasitol., 40, 251-257. KAUFMANN,S.H.E. & KABELITZ,D. (1990), Gamma/delta T lymphocytes and heat shock proreins. Curr. Top. Microbiol. Immunol. (in press). LEAKE,E.S., MVRVm,Q.N. & WmaHT, M.J. (1984), Phagosomal membranes of Mycobacterium bovis BCG-immune alveolar macrophages are resistant to disruption by Mycobacterium tuberculosis H37Rv. Infect. Immun., 45, 443-446. MODLIN, R.L., PIRMEZ,C., HOFMANN,F.M., TORIGIAN,V., UYEMURA,K., SEA, T.H., BLOOM, B.R. & BRENNER,M.B. (1989), Lymphocytes bearing antigen-specific -~8T-cell receptors accumulate in human infectious disease lesions. Nature (Lond.), 339, 544-548. MOORE, M.W., CARBONE,F.R. & BEVAN,M.J. (1988), Introduction of soluble protein into the class I pathway of antigen processing and presentation. Cell, 54, 777-785. MUNK,M.E., GATRILL,A. & KAUFMANN,S.H.E. (1990), Antigen-specific target cell lysis and interleukin-2 secretion by Mycobacterium tuberculosis activated "r/8 T cells. J. Ira. munol. (in press). MULLER, I., COBBOLD,S.P., WALDMANN,H. & KAUFMANN,S.H.E. (1987), Impaired resistance against Mycobacterium tuberculosis infection after selective in vivo depletion of L3T4 + and Lyt2 + T cells. Infect. Immun., 55, 2037-2041. O'BRJEN, R., HAPP, M.P., DALLAS,A., PALMER,E. & KUBO, R. (1989), Stiumation of a major subset of lymphocytes expressing T-cell receptor ~ by an antigen derived from Mycobacterium tuberculosis. Cell, 57, 667-674. STEINHOFF,U. & KAUFMANN,S.H.E. (1988), Specific lysis by CD8 + T cells of Sehwann cells expressing Mycobacterium leprae antigens. Europ. J. lmmunol., 18, 973-976.
