Dissociation between delayed-type hypersensitivity and resistance to pathogenic mycobacteria demonstrated by T-cell clones

Mycobacterium tuberculosis-specific CD8+ T cells and their role in immunity

There are more cases of tuberculosis in the world today than at any other time in history. The global epidemic has generated intense interest into the immunological mechanisms that control infection. Although CD4+ T cells play a critical role in host immunity to Mycobacterium tuberculosis, there is considerable interest in understanding the role of other T cell subsets in preventing disease development following infection. CD8+ T cells are required for optimum host defense following M. tuberculosis infection, which has led to investigation into how this protective effect is mediated. A critical review of recent literature regarding the role of CD8+ T cells in protective immunity to M. tuberculosis infection is now required to address the strengths and weaknesses of these studies. In this article, we evaluate the evidence that CD8+ T cells are critical in immunity to M. tuberculosis infection. We discuss the specific mycobacterial proteins that are recognized by CD8+ T cells elicited during infection. Finally, we examine the effector mechanisms of CD8+ T cells generated during infection and synthesize recent studies to consider the protective roles that these T cells serve in vivo.

CD3+ cells transfer the hypersensitive granulomatous response to mycobacterial glycolipid trehalose 6,6′-dimycolate in mice

The granulomatous response is the characteristic histological feature ofMycobacterium tuberculosisinfection that is essential for organism containment. Trehalose 6,6-dimycolate (TDM), a cell-wall glycolipid present on most mycobacterial species, has been implicated in the pathogenesis ofM. tuberculosisinfection. TDM has potent immunoregulatory and inflammatory properties, and can be used to model granulomatous reactions that mimic, in part, pathology caused during active infection. This study examined the hypersensitive granulomatous response, focusing on cellular responses specific to TDM. Lungs from mice immunized with TDM emulsion demonstrated exacerbated histological damage, inflammation, and lymphocytic infiltration upon subsequent challenge with TDM. Splenocytes recovered from these mice demonstrated significant interferon (IFN)-γproduction during recall response to TDM, as well as increased production of proinflammatory mediators (tumour necrosis factor-α, interleukin-6 and macrophage inflammatory protein-1α). The exacerbated response could be adoptively transferred to naïve mice. Administration of non-adherent lymphocytes or purified CD3+cells from TDM-immunized mice led to increased inflammation, lymphocytic infiltration, and vascular endothelial cell damage upon challenge with TDM. Recipient mice that received immunized CD3+lymphocytes demonstrated significant increases in Th1-type cytokines and proinflammatory mediators in lung tissue following TDM challenge. When CD1d−/−mice were immunized with TDM, they failed to generate a specific IFN-γresponse, suggesting a role for this molecule in the generation of hypersensitivity. These experiments provide further evidence for the involvement of TDM-specific CD3+T cells in pathological damage elicited duringM. tuberculosisinfection.

Differences in components at delayed-type hypersensitivity reaction sites in mice immunized with either a protective or a nonprotective immunogen of Cryptococcus neoformans

Cell-mediated immunity is the major protective mechanism against Cryptococcus neoformans. Delayed swelling reactions, i.e., delayed-type hypersensitivity (DTH), in response to an intradermal injection of specific antigen are used as a means of detecting a cell-mediated immune (CMI) response to the antigen. We have found previously that the presence of an anticryptococcal DTH response in mice is not always indicative of protection against a cryptococcal infection. Using one immunogen that induces a protective anticryptococcal CMI response and one that induces a nonprotective response, we have shown that mice immunized with the protective immunogen undergo a classical DTH response characterized by mononuclear cell and neutrophil infiltrates and the presence of gamma interferon and NO. In contrast, immunization with the nonprotective immunogen results in an influx of primarily neutrophils and production of tumor necrosis factor alpha (TNF-alpha) at the DTH reaction site. Even when the anticryptococcal DTH response was augmented by blocking the down-regulator, CTLA-4 (CD152), on T cells in the mice given the nonprotective immunogen, the main leukocyte population infiltrating the DTH reaction site is the neutrophil. Although TNF-alpha is increased at the DTH reaction site in mice immunized with the nonprotective immunogen, it is unlikely that TNF-alpha activates the neutrophils, because the density of TNF receptors on the neutrophils is reduced below control levels. Uncoupling of DTH reactivity and protection has been demonstrated in other infectious-disease models; however, the mechanisms differ from our model. These findings stress the importance of defining the cascade of events occurring in response to various immunogens and establishing the relationships between protection and DTH reactions.

Determinants of vaccine-induced resistance in animal models of pulmonary tuberculosis

A more effective vaccine will be essential if the global tuberculosis (TB) pandemic is ever to be controlled. A large number of new tuberculosis vaccines have been developed, representing the whole range of modern strategies for vaccine formulation and delivery. There is currently no alternative to testing these new vaccines in experimental animals challenged with virulent Mycobacteriurn tuberculosis in order to assess their protective efficacy. Although such testing is being carried out in several animal species (mice, guinea pigs, rabbits), all rational models include pulmonary challenge with a low dose of virulent mycobacteria. The quantitative measures for TB vaccines include increased survival, amelioration of clinical signs and symptoms (e.g. prevention of weight loss), decreased lesion size, reduction in bacillary loads in the lungs, and prevention of extrapulmonary dissemination and hematogenous reseeding of the lung. Although the ultimate objective of vaccination in humans is to prevent transmission to susceptible contacts, no such measurement is being used in animal studies of new vaccines. The validation of an immunological "correlate of protection" is urgently needed. Candidates for such a correlate include antigen-specific interferon-gamma production by T cells of the memory phenotype (CD45RB(high) or mycobacterial killing by macrophages co-cultured with immune T cells. Additional animal models must be developed for vaccines designed to prevent endogenous reactivation or exogenous reinfection, or to be used as a adjunct to chemotherapy.

Effective, nonsensitizing vaccination with culture filtrate proteins against virulent Mycobacterium bovis infections in mice

Vaccination of mice with Mycobacterium bovis culture filtrate proteins (CFP), prepared in a variety of adjuvants (aluminum hydroxide, Quil-A, and dimethyldioctyldecyl ammonium bromide [DDA]), provided significant protection against an aerosol challenge of virulent M. bovis. Additionally, vaccination with CFP in DDA or Quil-A did not sensitize mice to M. bovis purified protein derivative.

Adequate expression of protective immunity in the absence of granuloma formation in Mycobacterium tuberculosis-infected mice with a disruption in the intracellular adhesion molecule 1 gene

It remains unknown whether the expression of cell-mediated protective immunity and the capacity to mount a delayed-type hypersensitivity (DTH) reaction in tuberculosis infection represent two manifestations of a basic response or are dissociable events. In this study, we present data in favor of the latter hypothesis, by showing that tuberculosis infection in the lungs of mice possessing only a truncated form of intracellular adhesion molecule 1 due to gene disruption was still adequately controlled by the expression of protective immunity in the absence of any sustained influx of macrophages and the lack of formation of appreciable granulomas. These animals also had no detectable DTH response to mycobacterial proteins in the footpad assay, indicating that the accumulation of blood-borne macrophages at sites of mycobacterial infection or antigen deposition is not essential to control of the infection. These data support the hypothesis that the DTH component of the cellular response is not protective but contributes by walling off the sites of infection to prevent dissemination and reactivation disease.

Characterization of T cells that confer a high degree of protective immunity against tuberculosis in mice after vaccination with tumor cells expressing mycobacterial hsp65

Mice vaccinated by injection with tumor cells expressing the Mycobacterium leprae gene for hsp65 acquire a remarkably high degree of protection against challenge with Mycobacterium tuberculosis. We used limiting-dilution analysis to assess the frequency of CD4+ CD8- and CD4- CD8+ splenocytes responding to mycobacterial hsp65 in such vaccinated mice. Cells of both phenotypes were present at very high and equal frequencies (approximately 1:100). Vaccination with live Mycobacterium bovis BCG also increased the frequencies of both phenotypes of hsp65-reactive cells equally (to approximately 1:2,500), whereas vaccination procedures that were not protective, with either dead BCG, hsp65 protein in incomplete Freund's adjuvant, or hsp65 mixed with tumor cells, resulted in preferential increase in CD4+ CD8- cells. Twelve CD4+ CD8- and twelve CD4- CD8+ hsp65-responsive T-cell clones were obtained and characterized. All showed conventional antigen recognition via major histocompatibility complex class II and class I pathways but differed in secretion of gamma interferon and interleukin 4 and cytotoxicity. In tests of antimycobacterial activity against M. tuberculosis, both in infected macrophages in vitro and by adoptive transfer of protection with T-cell clones injected into irradiated mice, the most effective clones were the most cytotoxic and secretion of gamma interferon made only a secondary contribution.

Role of T-cell subsets in protection, delayed type of hypersensitivity and granuloma formation during Yersinia enterocolitica infection in mice

Studies were undertaken with (C57BL/6 x DBA/2) B6D2 F1 mice as a prototype of a strain resistant to Y. enterocolitica. The growth of Y. enterocolitica in liver and spleen following intravenous infection was determined. Restriction of growth of Y. enterocolitica in the spleen and liver started, when a delayed type of hypersensitivity (DTH) became elicitable. Mice were treated with monoclonal antibodies (mAb) specific to T-cell surface markers; injection of these antibodies leads to marked depletion of the specific T-cell subset. After selective in vivo depletion the three characteristic T-cell mediated phenomena, DTH, anti-bacterial protection and granuloma formation were investigated. DTH to Y. enterocolitica soluble antigen was abolished in mice treated with anti-Thy1.2 or anti-CD4 mAbs, while anti-CD8 mAbs had no effect. The elimination of bacteria from the spleens of infected animals was inhibited by the application of either anti-Thy1.2 or anti-CD8 mAbs, while anti-CD4 mAbs had a marginal effect on anti-bacterial protection. The accelerated development of mononuclear cell foci in the liver of immune mice was also inhibited by the application of anti-CD4 and anti-CD8 mAbs. Thus, it appears that specific T-lymphocytes play an important role in murine Yersiniosis. The present model is valuable for the investigation of the cellular immune response to this important enteric pathogen.

CD8+ type 1 CD44hi CD45 RBlo T lymphocytes control intracellular Brucella abortus infection as demonstrated in major histocompatibility complex class I- and class II-deficient mice

Genetically engineered mice with a targeted disruption in the beta 2-microglobulin (beta 2-m) gene or the H2-I-A beta chain (A beta) which lack functional CD8+ or CD4+ T cells, respectively, were used to assess the role of T cell subsets in Brucella abortus infection. Murine brucellosis was markedly exacerbated in beta 2-m-deficient mice (beta 2-m-/-) compared to A beta mutant (A beta-/-) or C57BL/6 mice, strongly indicating that optimal resistance to B. abortus requires CD8+ T cells. Splenocytes from Brucella-primed beta 2-m-/-, A beta-/- and C57BL/6 mice exhibited a type 1 cytokine profile marked by elevated IFN-gamma mRNA expression and protein production, and basal levels of IL-2 and IL-4 transcripts. B. abortus did not induce secretion of TGF-beta 1, but substantial IL-10 activity was detected in spleen cell supernatants from all mouse strains studied. CD8+ T cells from A beta-/- and C57BL/6 mice displayed a CD44hi CD45RBlo phenotype and a type 1 cytokine transcription profile featuring high levels of IFN-gamma mRNA. Additionally, we have shown the ability of C57BL/6 CD8+ CTL to kill Brucella-infected macrophages. This study illustrates the predominant role of MHC class I-restricted T cells in controlling B. abortus infection.

Protection against tuberculosis by passive transfer with T-cell clones recognizing mycobacterial heat-shock protein 65

We have previously shown that mice vaccinated by injection with J774 macrophage-like tumour cells that expressed Mycobacterium leprae heat-shock protein (hsp) 65 as a transgene had acquired a remarkably high degree of protection against subsequent challenge with virulent M. tuberculosis. We show here that antigen-specific T cells cloned from spleens of such vaccinated animals can transfer a high level of protection to non-vaccinated recipients. The most efficient cells were of T-cell receptor (TCR) alpha beta+ and CD4- CD8+ type and specifically lysed mycobacteria-infected macrophages. These findings are consistent with the importance for protective immunity of engaging the endogenous antigen-presenting pathway to bias the immune response towards a cytolytic action against a mycobacterial antigen that is expressed at the surface of infected macrophages. TCR gamma delta+ and TCR alpha beta+ cells interacted synergistically.

Vaccination against tuberculosis: is BCG more sinned against than sinner?

While extensive experimental studies of tuberculosis (Tb) have provided the foundation data for the discovery of cell-mediated immunity, there remains much to be disclosed about the critical pathways of immunity involved in this infectious process and the factors necessary to produce protective immunity. Studies on the aetiology and pathology of this disease have failed to elucidate the mechanisms of protective immunity. Although Tb research has been neglected for the past 30 years, the re-emergence of Tb worldwide as a significant zoonotic disease has re-focused research in this area. Scientific solutions for the control of Tb in man or domestic animals have not been found using empirical methods. Composite studies involving animal models of experimental infection will be necessary to critically evaluate vaccine efficacy and eludiate the basic immunological mechanisms involved in both disease and immunity. Available data which suggest that disease-related hypersensitivity and immunity are dissociable highlight the prospect that immunity to infection may be induced without compromising the continued need for ongoing systems of immunodiagnosis to exclude disease. In populations with a high prevalence of disease it is likely that a combination of immunodiagnosis, chemotherapy and immunoprophylaxis will be required to eradicate the disease.

In vivo depletion of CD4 and CD8 T lymphocytes impairs Mycobacterium w vaccine-induced protection against M. tuberculosis in mice

In the present study we sought to determine the relative role of CD4 and CD8 T cells in Mycobacterium w-induced protective immunity against tuberculosis of mice by in vivo depletion with specific monoclonal antibodies (mAb). Mice were immunized first with M.w, 4 weeks later treated with anti-CD4, anti-CD8 or a combination of both mAb and subsequently infected with M. tuberculosis H37Rv i.v. Numbers of colony-forming units in animals depleted of CD4 T cells, CD8 T cells or both T cell populations were significantly higher than those in control mice receiving irrelevant mAb or no mAb. Cytokine production by T cell subsets was also determined by culturing the cells remaining after in vivo depletion in the presence or absence of mycobacterial antigens. CD8 (CD4 depleted) T cells produced lower levels of interferon-gamma than CD4 (CD8 depleted) T cells. These data suggest that both CD4 and CD8 T cells participate in resistance against tuberculosis induced by vaccination with M.w.

Effects of administration of anti-CD4 and anti-CD8 monoclonal antibodies on Mycobacterium paratuberculosis infection in intragastrically challenged mice

In this study, we examined the roles of CD4+ and CD8+ cells in resistance to experimental paratuberculosis. Mice received purified anti-CD4 or anti-CD8 monoclonal antibodies before intragastric challenge with Mycobacterium paratuberculosis and on a biweekly basis for six months. This resulted in sustained depletion of CD4+ and CD8+ cells as verified by flow cytometry analysis of spleen cells from M. paratuberculosis infected mice. Depletion of CD4+ or CD8+ cells did not enhance fecal shedding of M. paratuberculosis, bacillary multiplication in the liver and ceca, nor histopathologic damage to the intestinal tract, mesenteric lymph nodes, spleen and liver. These data suggest that cells other than CD4+ or CD8+ cells are important for host defense in experimental paratuberculosis.

Effects of purified anti-Lyt-2 mAb treatment on murine listeriosis: comparative roles of Lyt-2+ and L3T4+ cells in resistance to primary and secondary infection, delayed-type hypersensitivity and adoptive transfer of resistance

Mice treated with purified anti-Lyt-2 monoclonal antibody (mAb) displayed a delayed ability to eliminate a primary Listeria monocytogenes infection from their spleens. Elimination of listeriae from the liver was unimpaired by anti-Lyt-2 mAb treatment. Treatment with anti-L3T4 mAb, alone or in combination with anti-Lyt-2 mAb, resulted in similar increases in the numbers of listeriae recovered from the spleens at 7 days after challenge. Listeria-infected mice that had been treated with anti-Lyt-2 mAb alone developed a strong delayed-type hypersensitivity (DTH) response, although it was significantly reduced as compared to control listeria-infected mice. In contrast, treatment with anti-L3T4 mAb severely impaired the development of DTH in listeria-infected mice. Treatment with anti-Lyt-2 mAb and anti-L3T4 mAb, singly or in combination, did not prevent mice from developing increased anti-listeria resistance if they were then immunized with a sublethal dose of L. monocytogenes. Treatment of mice with anti-Lyt-2 mAb or anti-L3T4 mAb before immunization, however, reduced the ability of their spleen cells to transfer anti-listeria resistance to recipient mice. These results indicate that Lyt-2+ cells make substantial contributions to the resistance of mice to primary L. monocytogenes infection, and to the ability of spleen cells from listeria-immunized mice to transfer resistance to naive recipients.

Macrophage-activating T-cell factor(s) produced in an early phase of Legionella pneumophila infection in guinea pigs

Protective immunity of guinea pigs against Legionella pneumophila was studied by infecting the animals with a sublethal dose (about 2 x 10(4) CFU) of the organism. The bacteria multiplied in the liver, spleen, and lungs up to day 4 after the intraperitoneal infection. The live bacteria in these organs decreased quickly thereafter and were eliminated by day 7. A delayed-type skin reaction and lymphoproliferation of spleen cells to Formalin-killed L. pneumophila were detected from days 5 and 6, respectively, after infection. Peritoneal macrophages obtained from guinea pigs infected 6 days previously inhibited the intracellular growth of L. pneumophila. Antigen-stimulated spleen cell factor prepared from infected guinea pigs inhibited the intracellular growth of the organism in macrophages obtained from uninfected animals. Antigen-stimulated spleen cell factor prepared from spleen cells treated with anti-guinea pig T-cell monoclonal antibody did not inhibit growth. The activity of antigen-stimulated spleen cell factor was labile to pH 2 treatment, and the factor could not be absorbed by L. pneumophila antigen, suggesting that it contains gamma interferon. Our data show that T-cell-mediated immunity begins to work from an early period of infection with L. pneumophila in guinea pigs.

Francisella tularensis-specific T-cell clones are human leukocyte antigen class II restricted, secrete interleukin-2 and gamma interferon, and induce immunoglobulin production

T-cell clones (TLC) were established from a Francisella tularensis-vaccinated subject in order to study the cells responsive for cell-mediated immunity against F. tularensis. All the clones were human leukocyte antigen (HLA) class II restricted to one of the HLA-DR specificities of the original donor. The TLC cells were CD4+ and produced interleukin-2 and gamma interferon after stimulation with specific antigen. Seven of the eight clones tested assisted in the production of immunoglobulin G (IgG), IgA, and IgM antibodies.

Parasite exposure elicits a preferential T-cell response involved in protective immunity against Eimeria species in chickens primed by an internal-image anti-idiotypic antibody

Polyclonal anti-idiotype 1073 (anti-Id 1073), raised against a monoclonal antibody specific for the protective epitope(s) of Eimeria tenella sporozoites, induced cell-mediated immune (CMI) responses in bursectomized chickens. Whereas alhydrogel-adsorbed anti-Id 1073 was sufficient to engender the CMI response at 4 h after injection, induction of the CMI response at 24 h required both alhydrogel and muramyl dipeptide sterol. Exposure of immunized chickens to live parasites prompted a dichotomous effect on the CMI response engendered by anti-Id in that the 4-h CMI response was preferentially stimulated and the 24-h CMI response was down regulated. Both types of CMI response were transferable to naive chickens by T cells from anti-Id 1073 immune donors or by parasite-specific T cells from clones 21 and 27. These T-cell clones were generated from chickens immunized by repeated infections with E. tenella and showed in vitro proliferative responses to anti-Id 1073. The abilities of T cells from clone 21 to selectively transfer the 4-h CMI response and to generate gamma interferon to activate macrophages for their cytotoxic effects on Eimeria sporozoites correlate with the preferential stimulation by parasites of the 4-h CMI response in chickens immunized with anti-Id 1073. These data show that anti-Id 1073 mimics the protective epitope(s) of the parasite and primes chickens for protective CMI responses. Cytotoxic T cells, equivalent to the mammalian T-cell subset of the Lyt2+ phenotype, appear to be the primary effector T cells in the CMI response engendered by anti-Id 1073 against Eimeria parasites.

Vaccination with Mycobacterium bovis BCG affects the distribution of Fc receptor-bearing T lymphocytes in experimental pulmonary tuberculosis

Inbred strain 2 guinea pigs were vaccinated with Mycobacterium bovis BCG or were left unvaccinated and challenged 6 weeks later by the respiratory route with virulent Mycobacterium tuberculosis. By using a double rosette assay with isotype-specific antibody-coated ox and uncoated rabbit erythrocytes, the proportions of T lymphocytes bearing Fc receptors for immunoglobulin G (IgG) (T gamma cells) or IgM (T mu cells) were quantified in tissues taken from animals that were killed within 4 weeks postchallenge. Tuberculin reactivity in vivo and in vitro and antimycobacterial resistance were also measured. BCG vaccination protected the guinea pigs and resulted in significantly enhanced proportions of T mu cells in the blood during the first 3 weeks and in the spleen during weeks 2 and 3 postchallenge. Levels of T gamma cells declined in all tissues during the first 3 weeks of infection and were unaffected by prior vaccination with BCG. Increased proportions of T mu cells in the blood were accompanied by dramatic tuberculin skin reactions and purified protein derivative-induced lymphoproliferation in BCG-vaccinated guinea pigs during the first 2 weeks following virulent pulmonary challenge. Peak levels of T mu cells in the spleens of vaccinated animals at 2 weeks coincided with the first appearance of virulent mycobacteria in that organ. BCG vaccination appears to influence immunoregulatory events in pulmonary tuberculosis through effects on the distribution of IgM Fc receptor-bearing (T mu cell) T lymphocytes.

The generation of guinea pig T-cell lines reactive to antigens from Mycobacterium tuberculosis. Selected lines induce erythematous skin reactions

We describe methods for the development and partial characterization of antigen-specific T-cell lines from the guinea pig, which is the classical experimental animal in tuberculosis research. T cells were obtained from strain 2 guinea pigs immunized with BCG vaccine or with killed Mycobacterium tuberculosis in oil. T-cell lines were obtained from limited dilution cloning of antigen-stimulated, blast-enriched lymphocyte cultures. The lines were grown with weekly reseedings in the alternating absence and presence of mycobacterial antigen. Antigen reactivity of the cell lines was studied with lymphocyte stimulation tests. With these methods we have consistently obtained antigen-reactive cell lines. When injected in small numbers intradermally in the presence of antigen in syngeneic guinea pigs, some of these cell lines gave rise to antigen-specific erythematous tuberculin-like skin reactions. The skin reactions, which were usually without induration, were most pronounced after 24 h. Histological examinations of skin undergoing such reactions showed that the erythemas were not accompanied by mononuclear infiltrations. We expect that transfer experiments with guinea pig T-cell lines will prove useful tools in the analysis of the contribution of defined mycobacterial antigen preparations to tuberculosis immunity.

Immune response to vaccination

Effective immune responses requires a synchronization of a number of different physiological and immunological events. Effective vaccines simulate natural invasion of the body by microbes or parasites. The route of administration of vaccines contributes to the effectiveness of preventing or controlling local or systemic infections. Immune responses to microbial agents usually involve more than one mechanism. For instance, toxins may be neutralized by a single antibody, while cellular interactions are required for destruction of more complex microorganisms. These systems have been illustrated in this review.

T-cell subsets in delayed-type hypersensitivity, protection, and granuloma formation in primary and secondary Listeria infection in mice: superior role of Lyt-2+ cells in acquired immunity

Immunity to Listeria monocytogenes was studied in mice treated with rat monoclonal antibodies (MAbs) specific for the Thy-1.2, L3T4, and Lyt-2 T-cell markers. Three characteristic T-cell-mediated phenomena were investigated. Delayed-type hypersensitivity (DTH) to listerial antigen was totally abolished in mice treated with anti-Thy-1.2 or anti-L3T4 MAbs, whereas anti-Lyt-2 MAb treatment had no effect, regardless of whether the MAb was given during the induction or the expression of DTH. On the other hand, the elimination of bacteria from the spleens of infected animals was inhibited only by the application of either anti-Thy-1.2 MAb or anti-Lyt-2 MAb. This could be shown most impressively during the secondary infection of immune mice with a normally lethal dose of listeriae. In this situation, treatment with anti-Lyt-2 MAb sufficed to completely abolish immunologic memory, whereas anti-L3T4 MAb had only a marginal effect on antibacterial protection. However, the accelerated development of mononuclear cell foci in the livers of immune mice was inhibited by the application of both anti-L3T4 MAb and anti-Lyt-2 MAb. It is concluded that in murine listeriosis, DTH and acquired immunity to reinfection are dissociable phenomena. Although DTH is a function of L3T4+ T lymphocytes, Lyt-2+ T cells are necessary and sufficient for the expression of acquired resistance to L. monocytogenes. The roles of the different T-cell subsets in granuloma formation warrant further investigation.

The immune response to the cell wall of Mycobacterium bovis BCG

Mice were immunized with the cell wall of BCG suspended in an oil-in-saline emulsion, and examined against time for the emergence of T cell-mediated acquired immunity. Evidence is presented that shows that levels of acquired resistance expressed in these animals over the first month following inoculation, and which enabled them to substantially resist an intravenous challenge infection with Mycobacterium tuberculosis, were completely nonspecific in nature, in that they were equally well expressed in normal and T cell-deficient mice, and were present at a time when no protective T cell activity could be passively transferred from the inoculated host. Paradoxically, in contrast, weak but statistically significant protective immunity could be detected in the spleens of CW-immunized mice approximately 3 months after inoculation, at a time when the donor animals were devoid of resistance to rechallenge. Finally, evidence is presented that shows that the CW material, if given subcutaneously, is highly immunogenic for the generation of delayed-type hypersensitivity effector T cells; however, these cells do not themselves contribute to protective immunity.

Regulatory interactions between macrophages and T cells in Mycobacterium lepraemurium-specific T-cell activation

The antigen-specific proliferative response of draining lymph node cells was found to follow a similar pattern in both C57BL and BALB/c mice following subcutaneous infection with Mycobacterium lepraemurium (MLM), although the two strains differed in their ability to control bacterial growth at the site of infection. The proliferative response, which was maximal 1-2 weeks postinfection, was T-cell dependent as it was abrogated with anti-Thy 1.2 + C treatment. The response was also abrogated by pretreatment with anti-Lyt 1.2 + C and slightly reduced by treatment with anti-Lyt 2.2 + C. The decline in T-cell responsiveness, at least from 4 to 8 weeks postinfection, may have been associated with prostaglandin production by inflammatory macrophages, as it was partially restored by addition of indomethacin. Also highly purified T lymphocytes from lymph nodes taken 6-8 weeks postinfection gave a strong antigen-specific proliferative response when reconstituted with optimal numbers of syngeneic antigen-presenting cells from uninfected mice. Proliferation was inhibited by peritoneal macrophages from Corynebacterium parvum-pretreated mice and macrophages from C57BL but not BALB/c mice infected with M. lepraemurium which had been elicited with heat-killed (HK) MLM and thioglycollate. Resident peritoneal macrophages from both C57BL and BALB/c mice infected subcutaneously with M. lepraemurium were slightly more inhibitory than normal macrophages but not as inhibitory as macrophages from C. parvum-pretreated mice. Macrophage-dependent inhibition of T-cell proliferation was partially reversed by addition of indomethacin, suggesting these cells were not defective in processing and presentation of HK-MLM antigens, and that the inhibitory effects were associated with prostaglandin production. Resident peritoneal macrophages from both C57BL and BALB/c mice infected subcutaneously with M. lepraemurium produced comparable or slightly elevated levels of IL-1 on stimulation with LPS or HK-MLM.