Impaired resistance to Mycobacterium tuberculosis infection after selective in vivo depletion of L3T4+ and Lyt-2+ T cells

An essential role for endogenous interferon-gamma in the generation of protective T cells against Mycobacterium bovis BCG in mice

Protective CD4+ T cells against Mycobacterium bovis bacillus Calmette-Guérin (BCG), which are characterized by the ability to produce interferon-gamma (IFN-gamma), could be induced by immunization of mice with viable BCG but not with killed BCG. A high level of IFN-gamma mRNA was observed when normal spleen cells were stimulated with viable but not killed BCG. By comparing mice immunized with either viable or killed M. bovis BCG, it was found that a high level of IFN-gamma mRNA was expressed only after immunization with viable BCG. This finding prompted us to investigate the effect of neutralizing the IFN-gamma on the final generation of protective T cells against M. bovis BCG. When endogenous IFN-gamma was neutralized by administration of anti-IFN-gamma monoclonal antibody in mice immunized with viable BCG, the generation of protective T cells was significantly impaired, as revealed by the adoptive transfer of spleen T cells. The generation of BCG-specific, IFN-gamma-producing T cells was also abolished. These results clearly demonstrate that endogenous IFN-gamma actually plays a critical role in the generation of protective T cells against M. bovis BCG in vivo. Moreover, this study suggests that the lack of IFN-gamma-inducing ability is responsible for the inability of killed M. bovis BCG to induce protective T cells in mice.

Immunobiological properties of a 30 kDa secretory protein of Mycobacterium tuberculosis H37Ra

Six different secretory proteins of molecular weights (15, 26, 30, 41, 55 and 70 kDa) were isolated from 8-day-old culture filtrate of Mycobacterium tuberculosis H37Ra using different column chromatography techniques. These proteins were further examined for their ability to induce cell mediated (T-cell proliferation assay) and humoral immune response (ELISA) in mice immunized with total culture filtrate proteins. Out of six proteins, three proteins showed good reactivity. However, the activity was at a maximum with 30 kDa antigen. The immune response induced by 30 kDa antigen emulsified in Freund's incomplete adjuvant (FIA) was investigated and was found to be dose dependent. The T-cell response induced by this protein was skewed towards T-helper (Th1) cells as determined by the pronounced secretion of interleukin-2 (IL-2) and gamma-interferon (IFN-gamma). The protective activity of the 30 kDa protein was also evaluated and compared with reference to Bacillus Calmette Guerin (BCG) vaccine in the mice challenged with virulent M. tuberculosis H37Rv. The degree of protection afforded by the 30 kDa antigen on the basis of mortality and the significant decrease in c.f.u.'s recovered from different organs (lung, liver, spleen) after 30 days of challenge with LD50 of M. tuberculosis H37Rv was significantly higher in comparison to BCG vaccinated animals. However, the degree of immunity induced by this antigen decreased with time (when challenged 8 and 12 weeks post-immunization) but it was still comparable with BCG. These findings suggest that 30 kDa secretory protein of M. tuberculosis is the key immunoprotective antigen and may be a suitable candidate for the development of an alternative subunit vaccine against tuberculosis.

Induction of cytotoxic T-cell responses against culture filtrate antigens in Mycobacterium bovis bacillus Calmette-Guérin-infected mice

CD8+ T cells are essential for protection against mycobacteria, as is clearly demonstrated by the fatal outcome of experimental infection of beta-2 microglobulin knockout mice. However, the mechanisms and antigens (Ags) leading to CD8+ T-cell activation and regulation have been poorly characterized. Here we show that, upon immunization of major histocompatibility complex (MHC)-congenic mice with Mycobacterium bovis bacillus Calmette-Guérin (BCG), a cytotoxic response against BCG culture filtrate (CF) Ags (CFAgs) is induced in H-2b and H-2bxd haplotypes but not in H-2d haplotype. This response is mediated by CD8+ T cells and absolutely requires the activation of CD4+ T cells and their secretion of interleukin 2. The lack of cytotoxic response in H-2d mice cannot be explained by impaired cytokine production or by a defect in Ag presentation by H-2d macrophages. Using the MHC class I mutant B6.C-H-2bm13 mouse strain, we demonstrate that cytotoxic T lymphocytes (CTLs) recognize CFAgs exclusively in association with D(b) molecules. These Ags are cross-reactive in mycobacteria, since BCG-induced CTLs also recognize macrophages pulsed with CF from Mycobacterium tuberculosis H37Rv and H37Ra and from two virulent strains of M. bovis. Moreover, immunization with Mycobacterium kansasii induces CTLs able to lyse macrophages pulsed with BCG CF. Finally, we have found that these Ags can be characterized as hydrophilic proteins, since they do not bind to phenyl-Sepharose CL-4B. Our results indicate that MHC-linked genes exert a profound influence on the generation of CD8+ CTLs following BCG vaccination.

Dynamic changes in circulating and antigen-responsive T-cell subpopulations post-Mycobacterium bovis infection in cattle

Bovine tuberculosis is a threat to animal and human health in several countries. Greater understanding of the immunology of the disease is required to develop improved tests and vaccines. This study has used a model of bovine tuberculosis, established in the natural host, to investigate the dynamic changes that occur in the circulating T-cell subpopulations after infection. When the phenotypic composition of the peripheral blood lymphocytes was determined pre- and post-experimental infection, the response to disease comprised three phases. Firstly, the WC1/gamma delta T cells decreased and then increased, suggesting localization to developing lesions and clonal expansion. Secondly, the CD4:CD8 ratio increased. Thirdly, the CD4:CD8 ratio decreased to less than pre-infection measurements. The latter changes suggested sequential involvement of CD4 and then CD8 T cells. The proportion of cells expressing interleukin-2 receptor (IL-2R) also increased. Panels of T-cell clones were established at various stages post-infection and all clones that exhibited antigen responsiveness were phenotyped. T-cell clones from early infection were WC1/gamma delta and CD4 in phenotype, while CD8 clones appeared later in infection, eventually becoming dominant. Therefore, from in vivo and in vitro evidence, it was suggested that there is a dynamic progression in the T-cell subpopulations involved dominantly in responses to mycobacteria.

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.

T-cell lung granulomas induced by sepharose-coupled Mycobacterium tuberculosis protein antigens: immunosuppressive phenomena reversed with cyclophosphamide and indomethacin

We induced lung granulomas in BALB/c mice by intratracheal instillation of Sepharose beads coated with a Mycobacterium tuberculosis protein extract. Granulomas composed of macrophages and lymphocytes were induced. The granulomatous reaction reached its peak 3-7 days after challenge and lasted for approximately 1 month. Immunolabelling of tissue sections and bronchial washings revealed that granulomas were predominantly composed of T lymphocytes with the cytotoxic-suppressor phenotype (CD8+). Granulomas were associated with a significant decrease in anti-mycobacterial immunity manifested by a drop in delayed-type hypersensitivity reactions and antibody titres. The immunosuppressive phenomena were abolished with cyclophosphamide or indomethacin. Control granulomas induced with methylated bovine serum albumin (BSA) were smaller and composed by similar numbers of CD4+ and CD8+ cells. BSA granulomas did not alter antibody titres but they decreased delayed-type hypersensitivity to BSA which was restored to normal with indomethacin but not with cyclophosphamide. Our findings show that mycobacterial proteins anchored to Sepharose beads are granulomatogenic and that they preferentially recruit CD8+ cells which, together with locally produced prostaglandins, down-modulate cell-mediated and humoral immunity to mycobacterial antigens.

Characterization of an inhibitory seric factor from tuberculosis anergic patients that acts on non-adherent PPD reactive cells

Non-adherent cells from PPD+ tuberculosis patients (TBP PPD+) and from healthy individuals treated with whole tuberculosis anergic immune sera or with its protein A-Sepharose IgG fraction, or with sera fraction separated by PPD-Sepharose chromatography, were submitted to immunofluorescence assays. Anti-human IgG or IgM FITC-conjugate were used to reveal the assays, and results were expressed by a fluorescence percentage or fluorescence index. The presence of IgG over the surface of PPD+ non-adherent cells was detected. High fluorescence percentages were observed only in those PPD+ cells treated with whole anergic serum or with its IgG fraction. Positive fluorescence index values were obtained only in those PPD+ cells treated with anergic serum, meanwhile fluorescence index was always negative when non-bound fractions from PPD-Sepharose were used. Results suggest that non-adherent population are the cell targets for the serum inhibitory factor, which previously has been detected to inhibit antigen response in PPD reactive cells and, point out the specific behavior of this factor, since it was eliminate by PPD-Sepharose chromatography. The IgG nature of the factor was demonstrated by SDS-PAGE and immunoelectrophoresis.

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.

Cytolytic activity against mycobacterial antigens: differences between haemophiliacs with and without HIV infection

Although asymptomatic haemophiliacs have been shown to have abnormalities of their immune response, independent of HIV, clinical evidence of significant immunosuppression is limited. The only clinical report has been an outbreak of M. tuberculosis in which a group of haemophilic boys appeared unduly susceptible to infection. These boys are now all HIV seropositive. Along with a group of HIV seronegative children with coagulation disorders and non-haemophilic HIV seropositive men, these boys have been restudied to examine immune response to PPD. The HIV seropositive haemophilic boys that had had M. tuberculosis infection had reduced cytolytic response to PPD pulsed macrophages comparable to the non-haemophilic HIV seropositive men. The HIV seronegative children with coagulation disorders showed a reduction in cytolytic activity at low effector:target ratios compared to normal controls. In vitro studies showed that exogenous factor VIII concentrate could inhibit cytolytic activity to PPD pulsed macrophages. The possible role of chronic blood-borne virus infection and factor VIII concentrates in the original outbreak are discussed.

Increased gamma-delta T-lymphocyte response to Mycobacterium bovis BCG in major histocompatibility complex class I-deficient mice

Mice with a homologous deletion of the beta 2-microglobulin gene (beta 2m-) are deficient in class I major histocompatibility complex molecules (MHC) and consequently are deficient in CD8+ T cells. These beta 2m- mutant mice control the intraperitoneal growth of an avirulent vaccine strain of mycobacteria, Mycobacterium bovis BCG, after intraperitoneal infection similarly to normal mice. We show that beta 2m- mice have an increased gamma-delta (gamma delta) T-cell response after infection with live avirulent mycobacteria. beta 2m- mice have an earlier and more sustained rise in the proportion of intraperitoneal gamma delta T cells, averaging 17% of T cells, compared with 6% in normal mice, at 28 days after infection. Compared with the population in normal mice, gamma delta T cells in the spleens of beta 2m- mice averaged a higher proportion of the total T-cell population of the spleen on days 5, 8, and 14 after intraperitoneal infection. These data document the kinetics of gamma delta T cells reactive to mycobacterial antigens in vivo without class I MHC restriction and support a role for class I MHC and CD8+ T cells in the in vivo regulation of gamma delta T cells.

Inflammatory response following intranasal infection with Mycobacterium avium complex: role of T-cell subsets and gamma interferon

The role of CD4+ and CD8+ T cells in the response to intranasal infection with a Mycobacterium avium complex isolate (MAC) was investigated. Depletion of CD4+ T cells by injected antibody exacerbated infection in the lung, spleen, and liver. There were decreased numbers of inflammatory cells in the lungs of CD4-depleted mice and a significant decrease in lung cytotoxic activity. The neutrophil response was unaffected, and in CD4-depleted mice, unlike intact infected mice, these cells were found with large numbers of associated MAC. Purified CD4+ splenic T cells produced gamma interferon (IFN-gamma) in vitro in response to MAC antigen. IFN-gamma production by cultured spleen, lung, or mediastinal lymph node cells was markedly reduced in CD4-depleted mice. In contrast, CD8+ T cells did not produce IFN-gamma in vitro, and depletion of CD8+ T cells from infected mice had no effect on bacterial growth or lung cell activation. Depletion of IFN-gamma by injected monoclonal antibody had effects similar to those of CD4 depletion, namely, exacerbation of infection and decreased lung cell cytotoxicity. We conclude that CD4+ T cells are the main T cells involved in the lung response to MAC infection and that this response is at least partially dependent on the production of IFN-gamma.

Immune response to Mycobacterium bovis bacille Calmette Guérin infection in major histocompatibility complex class I- and II-deficient knock-out mice: contribution of CD4 and CD8 T cells to acquired resistance

Knock-out mice with defined major histocompatibility complex (MHC) deficiencies were infected intravenously with Mycobacterium bovis bacille Calmette Guérin (M. bovis BCG) to assess the relative impact of MHC class I- and II-dependent immune responses. Heterozygous control mice were capable of controlling growth of M. bovis BCG, although infection progressed chronically, as assessed by determination of colony-forming units. Furthermore, infected controls developed granulomatous lesions at the site of mycobacterial growth and delayed-type hypersensitivity (DTH) reactions after challenge with purified protein derivative of tuberculin. In vitro, spleen cells from heterozygous control mice produced high concentrations of interferon-gamma (IFN-gamma) after restimulation with mycobacterial antigens. In contrast, the MHC class II-deficient A beta-/- mice, which are virtually devoid of functional CD4 T cells, succumbed to M. bovis BCG infection. Furthermore, A beta-/- mice lacked DTH reactions to tuberculin and only few minute picnotic lesions were formed in livers of infected mice. Finally, spleen cells from infected A beta-/- mice failed to produce measurable IFN-gamma concentrations after restimulation in vitro with various mycobacterial antigen preparations. The capacity of beta 2-microglobulin (beta 2m)-deficient mice, which are devoid of CD8 alpha/beta T cells, to inhibit growth of M. bovis BCG was only slightly affected at low inocula, although significantly higher colony-forming units were detected in spleens. These knock-out mice developed strong DTH responses to tuberculin and their spleen cells produced high levels of IFN-gamma once reactivated by mycobacterial antigens. Furthermore, in livers of infected beta 2m-deficient mice, extravascular infiltrates developed which were more diffuse than those in infected control littermates. Remarkably, the beta 2m-deficient mice were substantially more susceptible to higher inocula of M. bovis BCG than their control littermates. Our data formally prove the essential role of MHC class II-dependent immune mechanisms in all relevant aspects of immunity to M. bovis BCG. In addition, our findings emphasize an important contribution of MHC class I-dependent immunity to effective anti-mycobacterial protection. We assume that CD4 T cells are highly effective in containing M. bovis BCG within distinct granulomatous lesions, but fail to eradicate their intracellular pathogens. It appears most likely that CD8 T cells are also required to achieve this goal.

Antigen provoking gamma interferon production in response to Mycobacterium bovis BCG and functional difference in T-cell responses to this antigen between viable and killed BCG-immunized mice

It has been shown that gamma interferon (IFN-gamma)-producing CD4+ T cells, which are generated only by immunization with viable bacteria, exert a significant role in protective immunity against mycobacteria in mice. In this study, we have tried to determine the antigen recognized by the T cells in search of a possible protective antigen. T cells from viable Mycobacterium bovis BCG-immunized mice were stimulated with several antigens, and IFN-gamma production was measured. Purified protein derivative and viable and killed BCG lysates caused significant IFN-gamma production, and almost the same level of IFN-gamma activity was detected in both groups stimulated with viable and killed BCG lysates. However, heat shock protein (HSP) 65 and HSP 70 were not a major antigen for IFN-gamma production. The antigen provoking IFN-gamma production is localized mainly in the membrane fraction of BCG cells, and the approximate molecular size was 18 kDa. On the other hand, T cells from killed BCG-immunized mice never responded to this antigen for IFN-gamma production, whereas they could mount a delayed-type hypersensitivity response. These results showed that the antigen provoking IFN-gamma production was present in killed as well as viable BCG. In addition to the antigen presentation by antigen-presenting cells, some kinds of differentiation factor (such as monokines) that are produced only by stimulation with viable cells seemed to be necessary for the development of IFN-gamma-producing T cells.

Interleukin-6 production during chronic experimental infection

The appearance of interleukin-6 (IL-6) in serum of mice was monitored during the course of chronic infection with either Brucella abortus vaccine strain 19 or a virulent Mycobacterium avium Complex (MAC) isolate. Serum IL-6 during brucella infection was higher than during infection with MAC, despite similar numbers of bacteria. Furthermore, IL-6 titres decreased after the peak of infection, falling to baseline levels before these chronic infections were eradicated. The ability of peritoneal cells or spleen cell suspensions to produce IL-6 under either specific or non-specific stimulus was greatly enhanced by infection. While production of IL-6 by these cultures was apparently mostly independent of T cells, T cells from infected mice could produce an IL-6 response. Thus CD4+ T lymphocytes prepared from mice which had recovered from B. abortus infection, cultured with antigen and antigen presenting cells, resulted in IL-6 production, which was not observed in similarly cultured CD8+ T cells, indicating a role for T cells.

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.

Antigen-dependent in vitro culture of protective T cells from BCG-primed mice

Induction of protective immunity against pathogenic mycobacteria depends on vaccination with live organisms such as Bacille Calmette-Guérin (BCG). However, it is not known how many and which antigens are involved in the protective host response. In this study, we developed a system of antigen-dependent in vitro culture which is suitable for the analysis of protective subunits, presented in a soluble form. Spleen cells from Mycobacterium bovis BCG-immune mice, enriched for T cells and depleted of adherent cells on a column of G-10 Sephadex, were cultured for periods varying between 3 and 14 days before transfer and challenge with M. tuberculosis in irradiated hosts. Following 10 days in culture, immune T cells sustained their capacity to transfer protection to tuberculous infection when incubated in the presence of either live BCG or a soluble extract from M. tuberculosis, but lost this ability when cultured in the absence of antigen, or in the presence of the polyclonal mitogen concanavalin A. One immunodominant antigen, represented by the recombinant 38-kD antigen, failed to sustain the adoptive protection, despite pronounced stimulation of lymphoproliferation in culture. Antigenic in vitro stimulation of protective T cells was accompanied by enhanced responsiveness to exogenous IL-2. The experimental system described may be generally suitable to test in vitro the protective potentials of soluble molecular subunits of mycobacteria.

Tuberculosis--immunopathogenesis and therapy

Infection with Mycobacterium tuberculosis (TB) has returned to the forefront of public and medical concern because of the recent sharp increase in the number of cases. Major strides have been made in understanding the pathogenesis of TB, and some of these basic advances are being applied clinically. This review focuses on current concepts of the host response to TB, the changing epidemiology of TB, and optimal treatment strategies.

Major histocompatibility complex class I-restricted T cells are required for resistance to Mycobacterium tuberculosis infection

Mice with a targeted disruption in the beta 2-microglobulin (beta 2m) gene, which lack major histocompatibility complex class I molecules and consequently fail to develop functional CD8 T cells, provided a useful model for assessing the role of class I-restricted T cells in resistance to infection with virulent Mycobacterium tuberculosis. Of mutant beta 2m-/-mice infected with virulent 10(6) M. tuberculosis, 70% were dead or moribund after 6 weeks, while all control mice expressing the beta 2m gene remained alive for > 20 weeks. Granuloma formation occurred in mutant and control mice, but far greater numbers of tubercle bacilli were present in the lungs of mutant mice than in controls, and caseating necrosis was seen only in beta 2m-/-lungs. In contrast, no differences were seen in the course of infection of mutant and control mice with an avirulent vaccine strain, bacille Calmette-Guérin (BCG). Immunization with BCG vaccine prolonged survival of beta 2m-/-mice after challenge with M. tuberculosis for 4 weeks but did not protect them from death. These data indicate that functional CD8 T cells, and possibly T cells bearing gamma delta antigen receptor, are a necessary component of a protective immune response to M. tuberculosis in mice.

Generation of cytolytic T cells in individuals infected by Mycobacterium tuberculosis and vaccinated with BCG

BACKGROUND

Macrophage activation by cytokines provides only a partial explanation of antimycobacterial immunity in man. Because cytolytic T lymphocytes have been shown to contribute to immunity in animal models of intracellular infection, the generation of mycobacterial antigen specific cytotoxic T cells was examined in the peripheral blood of patients with tuberculosis.

METHODS

Subjects comprised 36 patients with active tuberculosis (18 newly diagnosed) and 32 healthy volunteers, of whom 25 had had BCG vaccination and seven were Mantoux negative. The ability of purified protein derivative (PPD) stimulated peripheral blood lymphocytes to lyse autologous, mycobacterial antigen bearing macrophages was examined by using a chromium 51 release assay.

RESULTS

PPD stimulated lymphocytes from normal, Mantoux positive, BCG vaccinated subjects produced high levels of PPD specific cytolysis, whereas lymphocytes from unvaccinated, uninfected subjects caused little or no cytolysis. The generation of cytolytic T lymphocytes by patients with tuberculosis was related to their clinical state. Those with cavitating pulmonary disease or lymph node tuberculosis generated PPD specific lymphocytes with cytotoxic ability similar to that of those from Mantoux positive control subjects, whereas lymphocytes from patients with non-cavitating pulmonary infiltrates showed poor antigen specific cytolysis. After seven days of stimulation with PPD in vitro, lymphoblasts contained both CD4+ and CD8+ cells. Mycobacterial antigen specific cytolysis was restricted to the CD4+ cell population and was blocked by monoclonal antibodies directed against major histocompatibility class II (MHC) antigens.

CONCLUSION

CD4+ cytolytic T cells can lyse autologous macrophages presenting mycobacterial antigen and were found in patients with cavitating pulmonary tuberculosis or tuberculous lymphadenitis and in normal, Mantoux positive control subjects. The ability to generate these T cell responses seems to be a marker for response to mycobacteria and may contribute to tissue damage in tuberculosis. These responses do not provide protective immunity against Mycobacterium tuberculosis but may help in disease localisation.

Theileria parva: CD4+ helper and cytotoxic T-cell clones react with a schizont-derived antigen associated with the surface of Theileria parva-infected lymphocytes

Theileria parva is a protozoan parasite which infects and transforms bovine lymphocytes, resulting in a fatal lymphoproliferative disease. There is evidence that immunity to the intralymphocytic schizont stage is mediated by T cells. We have previously reported derivation of CD4+ T-cell clones which recognize parasite-derived antigens presented on the surface of infected cells in conjunction with MHC molecules and partial characterization of the antigens. The present study further evaluated one of these antigens, demonstrating that it could be derived from cells infected with different parasite stocks as well as from purified theilerial schizonts and that it was recognized by primed, but not unprimed, bovine lymphocytes including cytolytic CD4+ T cells. Using a cloned CD4+ cytolytic cell line, lysis of schizont-infected cells was shown to be MHC-restricted but not parasite-strain restricted. In addition we demonstrated that T cells which respond to the HSS antigen preparation were generated in cattle immunized with parasites from any of the three subspecies of T. parva. The antigenic material was fractionated by sequential subjection to anion-exchange chromatography, hydroxylapatite chromatography, and gel filtration using HPLC, which resulted in recovery of approximately 20% of the antigenic material with more than 10(6)-fold purification in selected fractions. To assess the molecular size of the proteins in the highly purified antigenic fractions, the T. parva-infected lymphocytes were metabolically labeled before fractionation with 3H-amino acids and the material was analyzed by SDS-polyacrylamide gel electrophoresis and liquid scintillation counting of gel slices. The major protein in these fractions had a molecular mass of 9-10 kDa.

Antigen-specific cytolysis of infected cells in murine candidiasis

Immune L3T4+ and Lyt-2+ lymphocytes play an important role in the acquired resistance of mice to challenge with virulent Candida albicans, and release macrophage-activating cytokines in response to yeast cells in vitro. To determine whether antigen (Ag)-specific cytotoxic T lymphocytes are generated during fungal infection, purified L3T4+ and Lyt-2+ lymphocytes from immunized mice were cultured in the presence of syngeneic accessory cells, Candida Ag, and IL-2. Yeast-infected bone marrow macrophages and peritoneal exudate neutrophils were used as target cells in a standard 51Cr release assay. Ag-specific, MHC-unrestricted lysis of infected macrophages was evident with immune Lyt-2+ cells after 5-10 days in culture. Under the same experimental conditions, the cytotoxic activity of L3T4+ cells was negligible, but its expression could be induced by the addition of anti-CD3 antibody. Culturing immune Lyt-2+ cells for shorter periods of time (1-2 days) resulted in preferential lysis of infected neutrophils. In addition, at limiting effector cell numbers, Ag-specific MHC-restricted lymphocytes with cytotoxic activity to infected macrophages could be identified. We suggest that C. albicans infection stimulates multiple cytotoxic T-cell precursors with varying recognition stringency, which may have an important role in antifungal resistance in vivo.

Gamma interferon and interleukin 2, but not interleukin 4, are detectable in gamma/delta T-cell cultures after activation with bacteria

Mycobacterium tuberculosis- or group A streptococcus-activated gamma/delta T cells from normal healthy individuals were negatively sorted and restimulated in vitro from 48 h. Significant amounts of gamma interferon were detected after restimulation with M. tuberculosis, group A streptococci, or Listeria monocytogenes. In contrast, interleukin 4 was undetectable in the culture supernatants. Our findings provide indirect evidence for the involvement of gamma/delta T cells in immunity against tubercle bacilli and probably other bacteria.

In vitro characterization of T cells from Mycobacterium w-vaccinated mice

Tuberculosis caused by the intracellular bacterial pathogen Mycobacterium tuberculosis still represents a major health problem, and its effective control would best be accomplished by active vaccination. Although vaccination with M. bovis BCG has proven highly effective in certain parts of the world, in several developing countries it has been found to confer only marginal protection. Hence, novel vaccination strategies are warranted. Mycobacterium w is a saprophytic cultivable mycobacterium which shares several antigens with M. tuberculosis. In the murine system, vaccination with killed M. w was found to protect against subsequent tuberculosis. In order to characterize the responsible immune mechanisms more precisely, mice were vaccinated with killed M. w and T cells restimulated in vitro with mycobacterial antigens. These T cells produced interleukin 2 and gamma interferon but no detectable interleukin 4 and interleukin 5. Killed M. w induced significantly stronger T-cell responses than killed M. tuberculosis, and both vaccination regimes were markedly improved by administration in a mild adjuvant, i.e., the Ribi adjuvant containing trehalose dimycolate, monophosphoryl lipid A, and mycobacterial cell wall skeleton. Our data suggest that M. w-induced immunity against M. tuberculosis rests primarily on TH1 cells, which are thought to be of major relevance for acquired antituberculosis resistance. Our study therefore provides a further step toward the identification of a novel tuberculosis vaccine.

Strain differences in mouse cellular responses to Mycobacterium lepraemurium and BCG subcutaneous infections. II. Production of interleukins 2, 4, and 6 and of interferon-gamma by draining lymph node cells

C57BL/6, BALB/c, and CBA mice were infected either by Mycobacterium bovis BCG or by M. lepraemurium (MLM). Interleukins (IL) 2, 4 and 6 and interferon-gamma (IFN-gamma) were measured in the supernatants of draining lymph node cells (DLN) or control lymph node cells from uninfected mice, restimulated in vitro by the heat-killed infecting Mycobacterium. Uninfected lymph node cells did not develop any IL4, IL2, and IFN-gamma response to BCG and MLM. A significant IL6 response to BCG was observed, with CBA being the best producer and C57BL/6 the weakest. BCG-infected mice, which controlled the BCG infection, displayed variable patterns of lymphokine response to BCG according to the strain. C57BL/6 DLN cells produced more IL6 and IFN-gamma than IL2, whereas BALB/c mice produced more IL2. CBA secreted lymphokines with a similar pattern to that of BALB/c but in lower amounts. IL4 was not detected in any supernatant. MLM-infected mice displayed variable susceptibilities to MLM infection: C57BL/6 was resistant, BALB/c was susceptible after an initial efficient control, and CBA was fully susceptible. In each strain the lymphokine response to MLM was much lower than that triggered by BCG, but the pattern was similar. Thus, C57BL/6 DLN cells still produced significants amounts of IL2, IL6, and IFN-gamma, whereas BALB/c secreted IL2 alone and CBA did not produce any detectable lymphokine. IL4 was again not detected in any supernatant. The failure of BALB/c and CBA strains to develop IFN-gamma and IL6 responses to MLM might contribute to their low resistance to this infection.

CD4+ T cells regulate the magnitude of the antibody response to several helper T cell independent antigens

The effect of prior depletion of CD4+ T cells on the magnitude of the primary antibody response to several antigens considered to be helper T cell independent (TI) was examined. Treatment of mice with the monoclonal antibody GK1.5 to remove CD4+ T cells had little effect on the magnitude of the specific antibody response to the lipopolysaccharide (LPS) of Escherichia coli 0113; however, such treatment reduced the magnitude of the splenic IgM antibody response to E. coli 055 LPS, Serratia marcescens LPS, TNP-Ficoll, and Type III pneumococcal polysaccharide (SSS-III), compared to control untreated or rat IgG treated mice. Thus, CD4+ T cells positively influence of magnitude of the antibody response to the majority of helper T cell independent antigens tested.

Human Mycobacterium tuberculosis-reactive CD4+ T-cell clones: heterogeneity in antigen recognition, cytokine production, and cytotoxicity for mononuclear phagocytes

CD4+ T cells regulate the protective immune response which follows exposure to Mycobacterium tuberculosis by activating macrophages through the cytokines the CD4+ T cells secrete. In addition CD4+ T cells have been shown to be directly cytotoxic for antigen-pulsed mononuclear phagocytes (monocytes-macrophages). To explore the functional interaction between mycobacterial antigen-specific CD4+ T cells and mononuclear phagocytes further, CD4+ T-cell clones were derived from healthy purified protein derivative-positive individuals. Five T-cell clones were selected for detailed analysis. None responded to the purified recombinant or native mycobacterial antigens of 14, 19, 65, 71, and 30 (alpha-antigen/Ag6) kDa. However, the T-cell clones demonstrated heterogeneity in antigen recognition as measured by their Western blot (immunoblot) responses. Some T-cell clones made only interleukin 2, while others made only interleukin 4; all produced gamma interferon, although in differing amounts. Four of five T-cells clones were cytotoxic for purified protein derivative-pulsed monocytes at 1:1 and 10:1 effector-target cell ratios. When monocytes infected with live M. tuberculosis were used as targets, comparable levels of cytotoxicity were observed. The cytotoxicity was major histocompatibility complex class II restricted and inhibited by antibodies to ICAM-1 and LFA-1 and not by antibodies to tumor necrosis factor alpha, lymphotoxin, and gamma interferon. Cytotoxicity by CD4+ T cells for monocytes pulsed with mycobacterial antigens or infected with live M. tuberculosis is a common property of these cells and appears to be independent of the repertoire of lymphokines produced and not limited to recognition of defined mycobacterial heat shock proteins. Lysis of heavily infected mononuclear phagocytes may be one manner in which CD4+ T cells regulate host immune response to M. tuberculosis.

New use of BCG for recombinant vaccines

BCG, a live attenuated tubercle bacillus, is the most widely used vaccine in the world and is also a useful vaccine vehicle for delivering protective antigens of multiple pathogens. Extrachromosomal and integrative expression vectors carrying the regulatory sequences for major BCG heat-shock proteins have been developed to allow expression of foreign antigens in BCG. These recombinant BCG strains can elicit long-lasting humoral and cellular immune responses to foreign antigens in mice.

Memory T cell-mediated resistance to Mycobacterium tuberculosis infection in innately susceptible and resistant mice

The memory T cell immune response to Mycobacterium tuberculosis infection was examined in strains of mice which vary in their natural susceptibility to Mycobacterium bovis BCG infection. Naturally susceptible (NS) C57BL/6 and naturally resistant (NR) B6D2 F1 hybrid mice were infected with a sublethal dose of M. tuberculosis and then given antibiotic therapy beginning 2 weeks postinfection. T cells from both strains of mice transferred significant levels of resistance to syngeneic mice challenged aerogenically with M. tuberculosis. This memory response was not substantially reduced by depletion of either L3T4+ or Lyt2+ T cells from the donor mice but was ablated by depletion of both T cell subsets. Cyclophosphamide pretreatment of C57BL/6 memory T cell donors also ablated the resistance transferred to recipient mice. In contrast, B6D2 memory T cells were not affected by cyclophosphamide treatment, suggesting that differences may exist in the metabolic state of the memory T cells in the two donor strains, despite the fact that they both develop similar levels of acquired resistance to a subsequent tuberculous challenge.

Evaluación de las subpoblaciones de linfocitos T en pacientes tuberculosos empleand la modulación con teofilina

Se evaluaron las poblaciones y subpoblaciones linfocitarias en pacientes con tuberculosis pulmonar antes y durante la terapia relacionando estos valores con la incidencia y evolución de la enfermedad. Pacientes en sus diversas manifestaciones clínicas, vírgenes de tratamiento, se estudiaron por baciloscopía (BAAR), radiología, i.d.r. Mantoux y análisis complementarios. Se cuantificaron mediante la prueba de Rosetas espontáneas (RE) linfocitos T totales y activos (RE a 4ºC y 37ºC), T colaboradores (RE Teofilina Resistentes: RETR) y supresores (RE Teofilina Sensibles: RETS). Los exámenes se repitieron en los mismos sujetos iniciado el tratamiento y en testigos sanos (TS). Se demostró en los pacientes en todas sus formas clínicas un descenso significativo en los valores relativos y absolutos de células T y en la relación RETR/RETS (menor de 1). Existe asociación entre la forma clínica y el número de linfocitos T colaboradores. Los pacientes en tratamiento con evolución favorable, evidenciaron un incremento significativo en los linfocitos T totales, activos, colaboradores y en la relación RETR/RETS. Los enfermos con baciloscopía altamente positiva presentaron i.d.r. Mantoux baja o negativa y marcado descenso de células inmunocompetentes. Se comprobó asociación entre estas tres variables, lo mismo que entre el estado nutricional y la predisposición a contraer la enfermedad.

T-cell proliferative response to antigens secreted by Mycobacterium tuberculosis

An infection model of human tuberculosis was established with C57BL/6J mice. The lymphocyte proliferative responses to antigens from Mycobacterium tuberculosis were investigated during the course of infection and compared with results obtained with a group of mice immunized with large amounts of killed bacteria. The two groups responded similarly to a number of mycobacterial antigens, but marked differences in responses against secreted antigens were found; only infected mice responded vigorously to these. The responding lymphocyte subpopulation was made up of L3T4+ T lymphocytes under restriction of the Ia molecule.

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.

Immunity to mycobacteria: possible role of alpha/beta and gamma/delta T lymphocytes

Immunity to pathogenic mycobacteria is mediated by T lymphocytes. The possible contribution of CD4 alpha/beta T cells, CD8 alpha/beta T cells and gamma/delta T cells as well as the possible role of interleukin-mediated macrophage activation and target cell lysis through direct cell contact is discussed. Furthermore, attempts to define mycobacterial antigens for T lymphocytes with particular emphasis on heat shock proteins are described. The data currently available suggest complex interactions between different T-cell types in immunity to mycobacteria.

T cells do not mediate the initial suppression of a Salmonella infection in the RES

The course of a sublethal salmonella infection was followed in mice rendered susceptible by irradiation, reconstituted with T-cell-depleted bone marrow from normal donors and given a synergistic pool of CD4 and CD8 monoclonal antibodies. The results indicate that the host response causing the early plateau and suppression of bacterial growth at the end of the first week of the infection, which is essential for survival, does not require T cells.

Specific lysis of mycobacterial antigen-bearing macrophages by class II MHC-restricted polyclonal T cell lines in healthy donors or patients with tuberculosis

The cytolytic capacity of mycobacterial antigen-stimulated peripheral blood mononuclear cells, from healthy Mantoux-positive volunteers and from patients with tuberculosis was investigated. Polyclonal T cell lines induced by 7 days of stimulation in vitro with PPD or a sonicate of Mycobacterium tuberculosis lysed both autologous macrophages and Epstein-Barr virus (EBV) transformed B cell lines which had been pulsed with mycobacterial antigens, to a greater extent than unpulsed target cells or target cells pulsed with an irrelevant antigen (streptokinase/streptodornase). The killing of mycobacterial antigen-pulsed macrophages and EBV-transformed B cell line targets was inhibited by monoclonal antibodies to MHC class II antigens but not by antibodies directed against MHC class I antigens. PPD-pulsed EBV-transformed lymphoblastoid cell lines (LCL) competitively inhibited the killing of mycobacterial antigen-pulsed macrophages, whereas natural killer (NK) sensitive K562 cells (with or without antigen pulsing) did not inhibit mycobacterial antigen-dependent cytolysis of macrophages. Patients with tuberculosis showed a spectrum of mycobacterial antigen-induced cytolytic capacity. Those with extensive tissue necrosis (e.g. cavitatory pulmonary tuberculosis or caseous, extrathoracic tuberculosis) had high levels while patients with disseminated (miliary) tuberculosis or disease refractory to treatment showed little evidence of mycobacterial antigen induced cytotoxicity. The ability of mycobacterial antigen-stimulated lymphoblasts to kill specific antigen-pulsed autologous macrophages was not significantly different between healthy donors and patients with tuberculosis. However, the 'mycobacterial antigen-specific' component of this cytolysis was significantly deficient (P less than 0.01) in patients. We conclude that mycobacterial antigen-specific cytotoxic T cell responses may play a significant part in the immune response to mycobacterial infection.

Strain differences in mouse cellular responses to Mycobacterium lepraemurium and BCG subcutaneous infections. I. Analysis of cell surface phenotype in local granulomas

C57BL/6, BALB/c and CBA mice were subcutaneously infected with either Mycobacterium lepraemurium (MLM) or BCG, and studied for bacillary growth, granuloma size of infected footpads and draining lymph nodes (DLN), and DLN cell surface phenotype. Whereas, BCG-infected mice controlled the infection and developed early and large granulomas, MLM-infected mice exhibited major strain variations in their resistance to the infection, as well as in the granuloma size and kinetics. C57BL/6 mice, highly resistant, displayed early and regressive granulomas; BALB/c mice showed lower resistance and early granulomas that grew continuously; CBA mice, highly susceptible, developed late, soft, phagocyte-rich granulomas. Important strain differences in lymph node lymphocyte subset distribution could be observed prior to any infection: C57BL/6 mice displayed higher B cell percentages than both of the other strains and BALB/c mice showed the highest CD4/CD8 ratios, followed by CBA and C57BL/6 mice. BCG and MLM infections both induced similar changes of these parameters in all three strains: that is a decrease of the B cell percentage and a decrease of the CD4/CD8 ratio, and the strain differences observed in uninfected mice persisted. On the other hand, DLN cells stimulated by the infecting bacillus and interleukin 2 also displayed an increase of the CD8 T cell percentage as compared with normal lymph node cells, but this phenomenon was much less pronounced in BALB/c mice, whether infected by MLM or BCG, and in MLM-infected CBA mice, than in BCG- or MLM-infected C57BL/6 (B6) mice. Thus the ability of C57BL/6 mice to generate an early and persistent CD8 T cell response to mycobacteria may contribute to their resistance to MLM.

The role of macrophage activation and of Bcg-encoded macrophage function(s) in the control of Mycobacterium avium infection in mice

Following the intraperitoneal inoculation of 2.5 x 10(8) colony-forming units of Mycobacterium avium strain ATCC 25291, there was bacillary growth in the liver, spleen and peritoneal cavity of C57BL/6, C57BL/10, DBA/1 and BALB/c mice whereas DBA/2, C3H/He, CBA/Ca and CD-1 mice controlled the infection showing constant or slightly decreasing numbers of viable bacteria in the liver and spleen and effective clearance of the bacilli from the peritoneal cavities. The acquisition of non-specific resistance (NSR) to Listeria monocytogenes during the infection by M. avium was high in C57BL/6, BALB/c and C3H/He mice and negligible in DBA/2 and CD-1 mice. The magnitude of the acquisition of NSR was reduced in T cell-deficient mice and was directly proportional to the dose of the inoculum of M. avium. The production of hydrogen peroxide by phorbol myristate acetate-stimulated peritoneal macrophages of M. avium-infected mice was higher in C57BL/6 and BALB/c mice than in CD-1, DBA/2 and C3H/He animals. BALB/c. Bcgr (C.D2) mice, unlike their congenic strain BALB/c, restricted bacterial growth following the intravenous inoculation of 2.5 x 10(8) CFU of M. avium as efficiently as DBA/2 mice. C.D2 and BALB/c peritoneal macrophages from infected mice produced similar amounts of H2O2 but BALB/c mice developed higher levels of NSR to listeria than C.D2 mice. The production of nitrite by peritoneal macrophages from infected mice was found to be enhanced in DBA/2 and C3H/He but not in BALB/c, C57BL/6, DC-1 and C.D2 mice. Resident peritoneal macrophages from C.D2 mice were more bacteriostatic in vitro for M. avium than macrophages from BALB/c mice. The same relative differences between the two macrophage populations were observed when the cells were activated with lymphokines. The results show that the populations were observed when the cells were activated with lymphokines. The results show that the resistance to M. avium infection in mice is under the control of the Bcg gene and that susceptibility may be due to some defect in macrophage antibacterial function not completely overcome by the activation of this phagocyte in the susceptible strains of mice.

Identification of heterologous monoclonal antibodies that cross-react with cervine leukocyte subpopulations

The degree to which cross-reactivity between monoclonal antibodies developed against cells of the human, mouse, bovine and ovine immune systems, and cells of the cervine immune system occurs was investigated. It was found that within the ruminants a considerable degree of cross-reactivity does exist while there is virtually none between the cervine and murine or human systems. The highest incidence of cross-reactivity was found between ovine monoclonals and cervine leukocytes (46% cross-reactive) with 25% of bovine monoclonal antibodies cross-reacting with deer leukocytes. Ovine monoclonals were found to be the most useful in identifying a wide range of cervine leukocyte subpopulations. Bioassays showed that ovine anti-class I and II monoclonals detected molecules on cervine leukocytes that are functionally similar to MHC antigens. The possibility that cross-reactive monoclonals detect similar subpopulations in both the homologous and heterologous species is discussed.

Lung defenses against opportunistic infections

This review has examined the possible role of CMI in providing protection against three pathogens that can be opportunists in the lung. Monoclonal antibodies that identify the cellular components of the immune response and recombinant cytokines are important tools to better understand how pulmonary immunity is regulated. Although not discussed in detail, recombinant microbial antigens are useful for understanding various aspects of protective immunity and immunosuppression as well as for advancing vaccine development. There are important problems to address in order to continue steady progress in understanding pulmonary defenses, including some of those mentioned in this brief review. There should be an increased use of infectious models that more closely mimic naturally occurring infections, and comparisons should be made between results obtained with parenteral versus intrapulmonary routes of infection.

Adoptive immunity to Mycobacterium bovis strain bacillus Calmette-Guérin by long-term cultured T-cell line in nude mice

Tuberculin-active peptide-reactive T-cell lines were established from the popliteal lymph node of BALB/cA mice immunized with heat-killed Mycobacterium tuberculosis to investigate the cellular mechanisms in the protective immunity of tuberculosis. These T-cell lines, consisting mainly of L3T4 surface antigen-positive cells, were transferred intravenously into nude mice infected with M. bovis strain bacillus Calmette-Guérin (BCG). Four or 6 weeks after transfer, footpad swelling and hepatic granuloma formation were observed and viable counts in the liver were decreased. Reduction of viable counts in the liver was obviously preceded by the hepatic granuloma formation. An effect of Lyt-2+ T cells which might be included in the inoculum could be ruled out by the experiment using T-cell lines pretreated with anti-Lyt-2 monoclonal antibody and complement. These results indicated that T cells required for protective immunity in these experiments belong to the L3T4-positive TDTH subset. However, their protective activity was inferior to that of freshly prepared immune lymph node T cells. From the observation of migration patterns of 51Cr-labelled T cells in BCG-infected nude mice, a relatively high proportion of freshly isolated T cells, but only a small part of T-cell line, deposited in the spleen of infected nude mice. This difference in migration pattern of freshly isolated and cultured T cells could be one of the reasons for the less in vivo anti-bacterial activity of the latter.

Mycobacterial disease, immunosuppression, and acquired immunodeficiency syndrome

The mycobacteria are an important group of acid-fast pathogens ranging from obligate intracellular parasites such as Mycobacterium leprae to environmental species such as M. gordonae and M. fortuitum. The latter may behave as opportunistic human pathogens if the host defenses have been depleted in some manner. The number and severity of such infections have increased markedly with the emergence of the acquired immunodeficiency syndrome (AIDS) epidemic. These nontuberculous mycobacteria tend to be less virulent for humans than M. tuberculosis, usually giving rise to self-limiting infections involving the cervical and mesenteric lymph nodes of young children. However, the more virulent serovars of M. avium complex can colonize the bronchial and intestinal mucosal surfaces of healthy individuals, becoming virtual members of the commensal gut microflora and thus giving rise to low levels of skin hypersensitivity to tuberculins prepared from M. avium and M. intracellulare. Systemic disease develops when the normal T-cell-mediated defenses become depleted as a result of old age, cancer chemotherapy, or infection with human immunodeficiency virus. As many as 50% of human immunodeficiency virus antibody-positive individuals develop mycobacterial infections at some time during their disease. Most isolates of M. avium complex from AIDS patients fall into serotypes 4 and 8. The presence of these drug-resistant mycobacteria in the lungs of the AIDS patient makes their effective clinical treatment virtually impossible. More effective chemotherapeutic, prophylactic, and immunotherapeutic reagents are urgently needed to treat this rapidly increasing patient population.

Serological response of patients with leprosy to a 28- to 30-kilodalton protein doublet from early cultures of Mycobacterium bovis BCG

Analysis by Western immunoblotting of Mycobacterium bovis BCG short-term culture filtrates with a pool of serum samples from lepromatous leprosy patients revealed an immunodominant protein doublet with apparent molecular masses of 28 and 30 kilodaltons (kDa). The humoral response to these antigens was also investigated by using individual serum samples from patients representative of the whole spectrum of leprosy and from tuberculosis patients, as well as from contacts of leprosy patients and control groups. The protein doublet was recognized by 92% of the sera from patients with lepromatous leprosy (51 of 56), whereas essentially negative results were obtained with sera from the other groups. Similar immunodominant bands were also detected by Western blotting analysis of sonic extracts of seven other slow- and fast-growing mycobacterial species, suggesting a broad distribution of these antigens within the genus. Analysis of the purified doublet by Western blotting after two-dimensional gel electrophoresis fractionation showed that the 28- and 30-kDa doublet consisted of at least five different components with pls from 5.2 to 5.7 and molecular masses from 28 to 31 kDa. These results indicate that the protein doublet could be used as a potential marker in the diagnosis of lepromatous leprosy.

Effect of cytotoxic monoclonal antibody depletion of T-lymphocyte subpopulations on bleomycin-induced lung damage in C57BL/6J mice

Treatment of cancer patients with the antitumor antibiotic bleomycin (BLM) is associated with lung damage which can progress to pulmonary fibrosis. Shortly after intratracheal (it) administration of BLM to experimental animals there is an influx of inflammatory cells into the lung. These inflammatory cells, consisting primarily of polymorphonuclear cells, monocytes and lymphocytes, are believed to modulate the pathogenesis of pulmonary fibrosis. The objective of the present study was to determine the role of specific T-lymphocyte subpopulations in this disease process following a single it administration of BLM to C57BL/6J mice. Specific in vivo T-lymphocyte subpopulation depletion was accomplished by multiple intraperitoneal administrations of cytotoxic monoclonal antibodies to mice prior to and following BLM administration. Acute lung damage was assessed by measuring levels of angiotensin-converting enzyme and total protein in the bronchoalveolar lavage fluid 7 days after BLM treatment while chronic fibrosis was assessed by total lung hydroxyproline 28 days after BLM. Although we were able to deplete lymph nodes and BAL of specific T-lymphocyte subpopulations we were unable to detect a difference in the extent or severity of either the acute or chronic stage of BLM-induced lung damage. These results suggest that BLM lung disease progresses unabated in C57BL/6J mice despite virtually complete depletion of either L3T4+ or Lyt-2+ T-lymphocytes. Although a greater than 80% decrease in Thy-1.2+ T-lymphocytes was accomplished, there was a residual population of Thy-1.2+ lymphocytes resistant to the cytotoxic antibody. It is possible, therefore, that this population of cells does play a role in the development of BLM lung disease.