Protective role of gamma/delta T cells and alpha/beta T cells in tuberculosis

An alphabeta T-cell-independent immunoprotective response towards gut coccidia is supported by gammadelta cells

Although gammadelta cells are commonly hypothesized to provide a 'first line of defence', gammadelta-cell-deficient mice are generally only marginally more susceptible to pathogens. Because gammadelta cells are enriched within epithelia, it is important to resolve whether immunoprotective capacity towards epithelial-tropic pathogens is absent from the gammadelta-cell compartment, or whether such activity is present but simply redundant with that of alphabeta T cells. In this work, following infection of the intestinal epithelium of alphabeta T-cell-deficient mice with the coccidian parasite, Eimeria vermiformis, gammadelta cells were shown to support the rapid activation of other lymphoid cells and to confer a transferable antipathogen effect that could be eradicated by neutralization of interferon-gamma. However, unlike alphabeta T cells, these effects of gammadelta cells showed no evidence of functional immunological memory. These results are directly relevant to coccidiosis, an economically significant disease of livestock, and should have general relevance to infections involving alphabeta T-cell deficiencies, e.g. cryptosporidiosis in patients with acquired immune deficiency syndrome (AIDS).

Genetic dissection of primary and secondary responses to a widespread natural pathogen of the gut, Eimeria vermiformis

Because most pathogens initially challenge the body at epithelial surfaces, it is important to dissect the mechanisms that underlie T-cell responses to infected epithelial cells in vivo. The coccidian parasites of the genus Eimeria are protozoan gut pathogens that elicit a potent, protective immune response in a wide range of host species. CD4+ alpha beta T cells and gamma interferon (IFN-gamma) are centrally implicated in the primary immunoprotective response. To define any additional requirements for the primary response and to develop a comparison between the primary and the secondary response, we have studied Eimeria infections of a broad range of genetically altered mice. We find that a full-strength primary response depends on beta(2)-microglobulin (class I major histocompatibility complex [MHC] and class II MHC and on IFN-gamma and interleukin-6 (IL-6) but not on TAP1, perforin, IL-4, Fas ligand, or inducible nitric oxide synthetase. Indeed, MHC class II-deficient and IFN-gamma-deficient mice are as susceptible to primary infection as mice deficient in all alpha beta T cells. Strikingly, the requirements for a highly effective alpha beta-T-cell-driven memory response are less stringent, requiring neither IFN-gamma nor IL-6 nor class I MHC. The class II MHC dependence was also reduced, with adoptively transferable immunity developing in MHC class II(-/-) mice. Besides the improved depiction of an immune response to a natural gut pathogen, the finding that effective memory can be elicited in the absence of primary effector responses appears to create latitude in the design of vaccine strategies.

Regulatory interactions of alphabeta and gammadelta T cells in glomerulonephritis

BACKGROUND

Several lines of evidence suggest that cellular immune mechanisms contribute to glomerulonephritis.

METHODS

The roles of alphabeta and gammadelta T cells in the pathogenesis of glomerulonephritis were investigated in a model of nephrotoxic nephritis in mice deficient in either T-cell population [T-cell receptor (TCR)beta and TCRdelta knockout mice]. The model, induced by the injection of rabbit anti-mouse glomerular basement membrane antibody, is characterized by the development of proteinuria and glomerular damage over a 21-day observation period in wild-type mice.

RESULTS

Mice deficient in either alphabeta or gammadelta T cells developed minimal proteinuria and glomerular lesions and had a significant reduction in macrophage accumulation compared with wild-type mice. In gammadelta T-cell-deficient mice, circulating levels and glomerular deposition of autologous IgG were comparable to wild-type levels, while alphabeta T-cell-deficient mice had no autologous IgG production. Autologous antibody production was not required for the development of glomerulonephritis since mice that lack IgG and B cells (micro-chain-/-) developed similar proteinuria to that observed in wild-type mice.

CONCLUSIONS

These studies suggest a proinflammatory role for both alphabeta and gammadelta T cells in glomerular injury, independent of the humoral response. This is the first demonstration, to our knowledge, that both T-cell subsets contribute to the progression of a disease, and it suggests that complex regulatory interactions between alphabeta and gammadelta T cells play a role in glomerular injury.

Reduced formation of granulomata in gamma(delta) T cell knockout BALB/c mice inoculated with Mycobacterium avium subsp. paratuberculosis

The role of gamma(delta) T cells in the bovine immune response to Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) infection is poorly understood. Accordingly, using BALB/c mice that are innately susceptible to M. paratuberculosis, we compared wild-type and gamma(delta) T cell knockout BALB/c mice to study the protective roles of gamma(delta) T cells in M. paratuberculosis infection. Ten-week-old mice were inoculated intraperitoneally with either a low dose (4 x 10(6) colony-forming units [CFU]/mouse) or a high dose (4 x 10(9) CFU/mouse) of M. paratuberculosis strain ATCC 19698. Histopathologic and morphometric examinations showed reductions in the number and area of granulomatous lesions in the liver of the knockout mice at 18 weeks after inoculation with either the low or the high dose of the mycobacteria. Furthermore, at 18 weeks after inoculation, the bacterial load in the spleens of the knockout mice inoculated with the high dose was significantly lower than that of wild-type mice. No differences were found in bacterial load between the knockout and the wild-type mice in the low-dose groups. In contrast, in the livers of wild-type mice inoculated with either the low or high mycobacterial dose, increased areas of epithelioid granulomata were observed and the granulomata became disseminated widely during the experimental period. These findings in model mice suggest that gamma(delta) T cells, rather than restricting mycobacterial growth, may play a crucial role in development of epithelioid granulomata similar to those seen consistently in bovine paratuberculosis. The results of this study may have relevance to our understanding of the pathogenesis of paratuberculosis in ruminants, in which a prominent number of gamma(delta) T cells exist in the lymphoid system.

Immunophenotypical characterization of the lymphocyte infiltrate in caprine pulmonary tuberculosis

A study was made of the immunophenotype of the lymphocytes associated with natural caprine pulmonary tuberculosis at four stages of the disease. Regardless of the stage, CD4(+)and CD8(+)T lymphocytes predominated in lung and mediastinal lymph node lesions, but gamma/delta T and B (IgM(+)) cells were seen only rarely. At the primary complex stage, CD4(+)cells outnumbered CD8(+)cells. At the stage of generalized tuberculosis, however, and still more at the post-primary stage, CD8(+)cells outnumbered CD4(+)cells. At the final stage (tuberculous pneumonia), CD4(+)and CD8(+)cells were present in low but approximately equal numbers.

[gamma][delta] cells: a right time and a right place for a conserved third way of protection

The tripartite subdivision of lymphocytes into B cells, alphabeta T cells, and gammadelta cells has been conserved seemingly since the emergence of jawed vertebrates, more than 450 million years ago. Yet, while we understand much about B cells and alphabeta T cells, we lack a compelling explanation for the evolutionary conservation of gammadelta cells. Such an explanation may soon be forthcoming as advances in unraveling the biochemistry of gammadelta cell interactions are reconciled with the abnormal phenotypes of gammadelta-deficient mice and with the striking differences in gammadelta cell activities in different strains and species. In this review, the properties of gammadelta cells form a basis for understanding gammadelta cell interactions with antigens and other cells that in turn form a basis for understanding immunoprotective and regulatory functions of gammadelta cells in vivo. We conclude by considering which gammadelta cell functions may be most critical.

Reconstitution of gammadelta T cell repertoire diversity after human allogeneic hematopoietic cell transplantation and the role of peripheral expansion of mature T cell population in the graft

We have examined the reconstitution of gammadelta T cell repertoire diversity after human allogeneic hematopoietic cell transplantation using a polymerase chain reaction (PCR)-based complementarity-determining region (CDR) 3 size spectratyping and DNA sequencing. The CDR3 complexity in the variable region of the T cell receptor (TCR)-delta chain was different amongst the individuals studied. Furthermore, CDR3 size distribution patterns of allogeneic hematopoietic cell transplant recipients were almost completely recovered by a few months after transplantation. In some patients, clonal predominance of the TCRDV1+ T cells became evident during the period after transplantation. In one particular donor/recipient pair, clonal predominance of TCRDV1+ T cells was already present in blood lymphocytes of the donor, and was also observed in the recipient after transplantation. Using this donor/recipient pair, we have questioned whether gammadelta T cell regeneration occurs via the peripheral expansion of mature T cells in the graft. In the donor lymphocytes, two expanding gammadelta T cell clones, which were demonstrated by CDR3 sequences of the TCR-delta chain, were recognized. These two clones were identified in the T cells from the recipient post transplant, but not before transplantation. One of the two clones was still detectable 1(1/2) years after the transplant procedure. These results strongly suggest that peripheral expansion of mature T cells in the graft is the principal pathway of gammadelta T cell regeneration after allogeneic hematopoietic cell transplantation in adults.

Co-stimulatory signals increase the reactivity of gammadelta T cells towards mycobacterial antigens

Although it has been shown that gammadelta T lymphocytes are able to react with different cell-associated or soluble antigens, the immune repertoire of these cells appears to be skewed to the recognition of mycobacterial antigens. We have studied the number and reactivity of gammadelta T cells towards several mycobacterial antigens in patients with tuberculosis and leprosy, as well as their healthy contacts and control individuals. We found an increased number of Vdelta2+ cells in healthy contacts (PPD+ and lepromin+) and tuberculoid leprosy patients. The gammadelta T cells from lepromatous leprosy showed a decreased response to all antigens tested, but some of these patients exhibited a significant response to the 30-kD glycoprotein of Mycobacterium tuberculosis. Interestingly, the reactivity of gammadelta T cells against mycobacterial antigens was significantly increased by costimulatory signals generated through CD7, LFA-1, CD50 and CD69 in all groups. However, signalling through CD69 did not enhance the responsiveness of gammadelta lymphocytes from lepromatous patients. On the other hand, the in vitro blockade of IL-10 with a specific antibody enhanced the cell proliferation of gammadelta lymphocytes from lepromatous leprosy patients, whereas exogenous IL-10 had an opposite effect in most individuals studied. These results suggest the potential role of different cell membrane receptors in the regulation of gammadelta T cell proliferation induced by mycobacteria, as well as the possible involvement of IL-10 in this phenomenon.

Protective effect of DNA immunization against mycobacterial infection is associated with the early emergence of interferon-gamma (IFN-gamma)-secreting lymphocytes

The development of more effective anti-tuberculosis (TB) vaccines would contribute to the global control of TB. Understanding the activated/memory T cell response to mycobacterial infection and identifying immunological correlates of protective immunity will facilitate the design and assessment of new candidate vaccines. Therefore, we investigated the kinetics of the CD4+ T cell response and IFN-gamma production in an intravenous challenge model of Mycobacterium bovis bacille Calmette-Guérin (BCG) before and after DNA immunization. Activated/memory CD4+ T cells, defined as CD44hiCD45RBlo, expanded following infection, peaking at 3-4 weeks, and decreased as the bacterial load fell. Activated/memory CD4+ T cells were the major source of IFN-gamma and the level of antigen-specific IFN-gamma-secreting lymphocytes, detected by ELISPOT, paralleled the changes in bacterial load. To examine the effects of a DNA vaccine, we immunized mice with a plasmid expressing the mycobacterial secreted antigen 85B (Ag85B). This led to a significant reduction in mycobacteria in the liver, spleen and lung. This protective effect was associated with the rapid emergence of antigen-specific IFN-gamma-secreting lymphocytes which were detected earlier, at day 4, and at higher levels than in infected animals immunized with a control vector. This early and increased response of IFN-gamma-secreting T cells may serve as a correlate of protective immunity for anti-TB vaccines.

gammadelta T cells may dichotomously modulate infection with avirulent Salmonella choleraesuis via IFN-gamma and IL-13 in mice

To investigate the roles of gammadelta T cells in Salmonella infection, we examined the resolution of an intraperitoneal infection with avirulent Salmonella choleraesuis 31N-1 in mice lacking T-cell-receptor (TCR) alphabeta T cells by disruption of the TCRbeta chain gene (TCRbeta(-/-)). The bacteria in TCRbeta(-/-) mice decreased with kinetics similar to that seen in control mice (TCRbeta(+/+)) after infection. The number of natural killer (NK) cells in the peritoneal cavity increased on day 6 after infection and thereafter decreased in both TCRbeta(-/-) and TCRbeta(+/+) mice, whereas the number of gammadelta T cells, in place of alphabeta T cells, increased remarkably in the peritoneal cavity of TCRbeta(-/-) mice on day 6 after infection. The NK cells from Salmonella-infected TCRbeta(-/-) mice produced interferon-gamma (IFN-gamma) but neither interleukin-4 (IL-4) nor IL-13 in response to immobilized anti-NK1.1 monoclonal antibody (mAb). The gammadelta T cells produced IFN-gamma but neither IL-4 nor IL-13 in response to heat-killed Salmonella, whereas both IFN-gamma and IL-13 but no IL-4 was produced by the gammadelta T cells stimulated with immobilized anti-TCRgammadelta mAb. In vivo administration of anti-NK1.1 mAb inhibited the reduction of Salmonella, whereas anti-TCRgammadelta mAb treatment did not affect the bacterial growth in TCRbeta(-/-) mice after Salmonella infection. However, neutralization of endogenous IL-13 with anti-IL-13 mAb enhanced the bacterial clearance in TCRbeta(-/-) mice after infection. These results suggest that NK1.1(+) cells serve mainly to protect against avirulent Salmonella infection in the absence of alphabeta T cells, whereas gammadelta T cells may play dichotomous roles in Salmonella infection through IFN-gamma and IL-13 in TCRbeta(-/-) mice.

Self-recognition of CD1 by gamma/delta T cells: implications for innate immunity

The specificity of immunoglobulins and alpha/beta T cell receptors (TCRs) provides a framework for the molecular basis of antigen recognition. Yet, evolution has preserved a separate lineage of gamma/delta antigen receptors that share characteristics of both immunoglobulins and alpha/beta TCRs but whose antigens remain poorly understood. We now show that T cells of the major tissue gamma/delta T cell subset recognize nonpolymorphic CD1c molecules. These T cells proliferated in response to CD1+ presenter cells, lysed CD1c+ targets, and released T helper type 1 (Th1) cytokines. The CD1c-reactive gamma/delta T cells were cytotoxic and used both perforin- and Fas-mediated cytotoxicity. Moreover, they produced granulysin, an important antimicrobial protein. Recognition of CD1c was TCR mediated, as recognition was transferred by transfection of the gamma/delta TCR. Importantly, all CD1c-reactive gamma/delta T cells express V delta 1 TCRs, the TCR expressed by most tissue gamma/delta T cells. Recognition by this tissue pool of gamma/delta T cells provides the human immune system with the capacity to respond rapidly to nonpolymorphic molecules on professional antigen presenting cells (APCs) in the absence of foreign antigens that may activate or eliminate the APCs. The presence of bactericidal granulysin suggests these cells may directly mediate host defense even before foreign antigen-specific T cells have differentiated.

Dominance of IL-12 over IL-4 in gamma delta T cell differentiation leads to default production of IFN-gamma: failure to down-regulate IL-12 receptor beta 2-chain expression

Gamma delta T cells secrete Th1- and Th2-like cytokines that help mediate innate and acquired immunity. We have addressed the mechanism whereby murine gamma delta T cells acquire the capacity to differentially produce such cytokines. Splenic gamma delta T cells could be polarized into IFN-gamma- or IL-4-secreting cells in vitro; however, in contrast to CD4+ alpha beta T cells, gamma delta T cells predominantly produced IFN-gamma, even in the presence of IL-4, a finding independent of genetic background. Like CD4+ Th1 cells, IFN-gamma-producing cells expressed the IL-12 receptor beta 2-chain after activation in the presence of IL-12; however, unlike Th2 cells, IL-4-primed gamma delta T cells also expressed this receptor, even in the absence of IFN-gamma and despite the presence of the transcription factor GATA-3. IL-12 also induced IL-4-primed gamma delta T cells to proliferate and to translocate Stat3/Stat4, indicating signaling through the IL-12 receptor. These molecular events can account for the predominant production of IFN-gamma by gamma delta T cells in the presence of IL-12, despite the availability of IL-4. Early and predominant production of IFN-gamma by gamma delta T cells likely is critical for the roles that these cells play in protection against intracellular pathogens and in tumor immunity.

Identification of distinct lymphocyte subsets responding to subcellular fractions of Mycobacterium bovis bacille calmette-Guérin (BCG)

In order to investigate the ability of Mycobacterium bovis BCG vaccination to induce immune responses toward different classes of mycobacterial antigens and the cell populations involved in such responses, proliferation of distinct human lymphocyte subsets from BCG-vaccinated donors in response to different subcellular fractions of BCG was analysed and compared with that of not sensitized subjects. Proliferation of different cell subsets was evaluated by flow cytometric determination of bromodeoxyuridine incorporated into DNA of dividing cells and simultaneous identification of cell surface markers. Although a certain degree of variability was observed among different donors, after 6 days of in vitro stimulation BCG-vaccinated subjects displayed, as a mean, a stronger blastogenic response to all the classes of antigens compared with non-sensitized ones. PPD, culture filtrates and membrane antigens induced a predominant proliferation of CD4+ T cells. In contrast, preparations enriched in cytosolic antigens elicited strong proliferation of gammadelta+ T cells which, as a mean, represented 55% of the proliferating cells. Although to a lesser extent, proliferation of gammadelta+ T cells was also elicited by preparations enriched in membrane and cell wall antigens. In response to the latter preparation proliferation of CD4+ T cells and CD16+/CD3- (natural killer (NK)) cells was observed, as well. In particular, cell wall antigens were found to induce significantly higher levels of proliferation of NK cells compared with all the other classes of antigens.

Escherichia coli infection induces only fetal thymus-derived gamma delta T cells at the infected site

Intraperitoneal infection of mice with Escherichia coli induced activated TCR gamma delta T cells in the peritoneal cavity. We provide evidence that the E. coli-induced gamma delta T cells are derived only from the fetal thymus on the following grounds. The gamma delta T cells were not induced in athymic nude mice and irradiated bone marrow-transferred mice which lack fetal thymus-derived T cells. However, E. coli infection of fetal thymus-grafted nude mice did induce fetal thymus-derived gamma delta T cells. These results suggest that the fetal thymus-derived gamma delta T cells colonize the periphery during early ontogeny, and are maintained until adult age. The E. coli-induced gamma delta T cells express only the Vdelta1 gene. Vgamma6 was predominantly expressed whereas anti-Vgamma1 and anti-Vgamma4 monoclonal antibodies stained less than 3 % of the cells. Direct sequencing of PCR products revealed that Vgamma6 and Vdelta1 genes expressed by the E. coli-induced gamma delta T cells were invariant sequences identical to those expressed in the fetal thymus. The antigen (Ag) specificity of a T cell hybridoma expressing the fetal type Vgamma6 / Vdelta1(+) TCR could not be identified as the cells failed to respond to lipopolysaccharide, E. coli Ag, mycobacterial heat shock protein 65, or isopentenyl pyrophosphate. These results suggest that the Vgamma6 / Vdelta1(+) gamma delta T cells derived from fetal thymus can participate in immune responses against bacterial infection through recognition of a novel class of Ag which is not yet identified.

Granuloma formation is required to contain bacillus growth and delay mortality in mice chronically infected with Mycobacterium tuberculosis

Previous studies in this laboratory have shown that mice with a gene disruption to the intracellular adhesion molecule-1 (ICAM-K/O) express normal cell-mediated immunity but cannot mount delayed-type hypersensitivity reactions following Mycobacterium tuberculosis infection. However, even in the absence of any appreciable granuloma formation, these mice control bacterial growth for at least 90 days. While not required to control the infection initially, we hypothesized that granuloma formation was required to control chronic infection, acting by surrounding infected cells to prevent bacterial dissemination. To test this, ICAM-1 knockout mice were infected with a low dose aerosol of M. tuberculosis Erdman and were found to succumb to infection 136+/-30 days later, displaying highly elevated bacterial loads compared to wild-type mice. Lung tissue from ICAM-K/O mice displayed extensive cellular infiltration and widespread tissue necrosis, but no organized granulomatous lesions were evident, whereas the control mice displayed organized compact granulomas. These data demonstrate that while a granulomatous response is not required initially to control M. tuberculosis infection, absence of granulomas during chronic infection leads to increased bacterial growth and host death. Thus these data support the hypothesis that granuloma formation is required to control chronic infection, acting by surrounding and walling off sites of infection to prevent bacterial dissemination and maintain a state of chronic infection.

Immune response against heat shock proteins in infectious diseases

Heat shock proteins (hsp) are conserved molecules that play an important role in protein folding and assembly and in translocation of proteins between different compartments. Under stress, hsp synthesis is drastically increased, representing a mechanism essential for cell survival. During infection or inflammation, numerous hsp are overexpressed. Not surprisingly, hsp represent dominant antigens in many infectious and autoimmune diseases that induce strong humoral and cellular immune responses. There is substantial evidence that hsp are dominant immune targets in a number of diseases, to the benefit or detriment of man. Nevertheless, findings also exist which argue against a universal role for hsp as target antigens in disease situations. It is suggested that hsp mainly serve as 'early' targets in the immune response, thus providing support for anti-infectious or autoaggressive immune responses directed against unique pathogen- or disease-associated antigens, respectively.

Different types of pulmonary granuloma necrosis in immunocompetent vs. TNFRp55-gene-deficient mice aerogenically infected with highly virulent Mycobacterium avium

The immunopathogenesis of mycobacterial infections frequently involves the formation of caseating granulomas which cause tissue destruction and, in the case of tuberculosis (TB), may lead to cavity formation. Both intravenous and aerosol models of Mycobacterium tuberculosis infection in mice do not reflect the pulmonary lesions characteristic of TB patients. Using both low-dose (10(2) colony-forming units, cfu) and high-dose (10(5) cfu) aerosol infection with a highly virulent strain of Mycobacterium avium (TMC724) in C57BL/6 mice, it is now shown that these mice are capable of developing centrally caseating necrosis in lung granulomas after approximately 4 months of infection. In contrast, mice infected intravenously with the high dose never developed this type of lesion, although bacterial counts in their lungs reached levels comparable to those attained by aerosol-infected mice (10(10) cfu). To study the relevance of events signalled by tumour necrosis factor (TNF) in this model, TNFRp55 gene-deficient and syngeneic C57BL/6 immunocompetent mice were infected with 10(5) cfu M. avium via aerosol. In gene-deficient mice, newly formed pulmonary granulomas acutely disintegrated, showing signs of apoptotic cell death and neutrophil influx, and TNFRp55 knock-out mice all succumbed to infection just beyond the stage of granuloma initiation. Aerogenic infection with M. avium in mice is a suitable model to study the immunopathogenesis of granuloma necrosis because it closely mimicks the histopathology of mycobacterial infections in humans, including TB. Furthermore, the use of TNFRp55 gene-deficient mice in this model establishes a role for TNF in maintaining the integrity of a developing pulmonary granuloma.

Generation of Nitric Oxide by the Inducible Nitric Oxide Synthase Protects γδ T Cells from Mycobacterium tuberculosis-Induced Apoptosis

γδ T cells are early recruited into mycobacterial lesions. Upon microbial Ag recognition, γδ cells secrete cytokines and chemokines and undergo apoptosis via CD95/CD95 ligand (CD95L) interaction, possibly influencing the outcome of infection and the characteristics of the disease. In this paper we show that activated phagocytes acquire, upon challenge with Mycobacterium tuberculosis, the ability to inhibit M. tuberculosis-induced γδ cell apoptosis. Apoptosis protection was due to NO because it correlated with NO synthase (NOS)-2 induction and activity in scavenger cells and was abrogated by NOS inhibitors. Furthermore, the NO donor S-nitrosoacetylpenicillamine mimicked the effect of enzyme induction. NO left unaffected the expression of CD95 and CD95L, suggesting interference with an event ensuing CD95/CD95L interaction. NO was found to interfere with the intracellular accumulation of ceramide and the activation of caspases, which were involved in γδ T cells apoptosis after M. tuberculosis recognition. We propose that NO generated by infected macrophages determines the life span and therefore the function of lymphocytes at the infection site, thus linking innate and adaptive immunity.

Characterization of the memory/activated T cells that mediate the long-lived host response against tuberculosis after bacillus Calmette-Guérin or DNA vaccination

The memory/activated T cells, which mediate the long-lived host response against tuberculosis, in mice immunized with either bacillus Calmette-Guérin (BCG) or mycobacterium heat-shock protein 65 (hsp 65) antigen expressed from plasmid DNA (DNA-hsp 65), were characterized. Protection against Mycobacterium tuberculosis challenge by DNA-hsp 65 vaccination was associated with the presence of lymph node T-cell populations in which CD8+/CD44hi interferon-gamma (IFN-gamma)-producing/cytotoxic cells were prominent even after 8 or 15 months of plasmid DNA-mediated immunizations, whereas after BCG vaccination the majority were CD4+/CD44lo IFN-gamma-producing T cells. When the cells were separated into CD4+CD8- and CD8+CD4- and then into CD44hi and CD44lo types, CD44lo cells were essentially unable to transfer protection in adoptive transfer experiments, the most protective CD44hi cells were CD8+CD4- and those from DNA-vaccinated mice were much more protective than those from BCG-immunized mice. The frequency of protective T cells and the level of protection were increased up to 8 months and decreased after 15 months following DNA or BCG immunizations.

Changes in T-lymphocyte subsets in lungs and spleens of mice with slowly progressive primary mycobacterium tuberculosis infection: involvement of unconventional T-cell subsets

Our previous study showed that the cell-activation responses and cytokine-secretion patterns were different in lungs and spleens of mice with slowly progressive primary Mycobacterium tuberculosis infection. The aim of the present study was to characterize the T-cell subsets in lungs and spleens of mice with a similar infection. The percentages of T-cell subsets were determined by flow cytometry and the absolute numbers were calculated. Spleens of infected mice showed a threefold expansion of CD4+ cells but no change in CD8+ cells, whereas lungs had a threefold increase of both subsets. A significant expansion of CD4-CD8-alphabeta+ [double negative (DN)alphabeta+] subsets was observed in the lungs of infected mice compared with uninfected mice. This was not the case in the spleens of infected mice. In infected mice the CD4-CD8- (DN) population preferentially expressed alphabeta-T-cell receptors (TCR) in the lungs but gammadelta-TCR in the spleens. The percentages of many T-cell subsets were significantly higher in the lungs than in the spleens of both uninfected and infected mice. However, the percentages of CD4+ and CD4-CD8+TCR- subsets in the lungs were significantly lower than in the spleens of infected mice. We also observed some previously unreported T-cell subsets: double positive-TCR- (DPTCR-), DPalphabeta+ and DPgammadelta+. So far their functions are unknown.

Fatal granuloma necrosis without exacerbated mycobacterial growth in tumor necrosis factor receptor p55 gene-deficient mice intravenously infected with Mycobacterium avium

The pathogenesis of mycobacterial infections is associated with the formation of granulomas in which both antibacterial protection and tissue damage take place concomitantly. We used murine Mycobacterium avium infection to compare the development of granulomatous lesions in intravenously infected tumor necrosis factor receptor p55 (TNFRp55) gene-deficient (p55(-/-)) mice to the development of granulomatous lesions in M. avium-infected syngeneic C57BL/6 (p55(+/+)) mice. Up to 5 weeks after infection with either the highly virulent M. avium strain TMC724 or the intermediately virulent M. avium strain SE01, bacterial counts in the liver, spleen, and lung of p55(-/-) mice were identical to or lower than those in infected p55(+/+) mice. However, the formation of mononuclear cell foci in the liver was delayed by approximately 2 to 3 weeks in p55(-/-) mice compared to the results obtained for infected p55(+/+) mice. Despite comparable bacterial loads, granulomas in p55(-/-) mice underwent progressive necrosis, causing damage to the surrounding liver tissue. The appearance of necrotizing granulomas was associated with the death of all infected p55(-/-) mice, regardless of the virulence of the M. avium strain used for infection. Granulomatous lesions in the liver contained three times as many CD3(+) cells in p55(-/-) mice yet appeared more diffuse than in p55(+/+) mice. Semiquantitative reverse transcription-PCR studies revealed that prior to mouse death, interleukin-12 (IL-12) and gamma interferon mRNA levels were up regulated in the livers of infected p55(-/-) mice, while mRNA levels for tumor necrosis factor, the inducible isoform of nitric-oxide synthase (iNOS), and IL-10 were similar to those found in infected p55(+/+) mice. In response to persistent mycobacterial infection, the absence of TNFRp55 causes the disregulation of T-cell-macrophage interactions and results in fatal granuloma necrosis even when adequate antibacterial functions are maintained.

Cytokine/chemokine cascades in immunity to tuberculosis

The relationship between acquired specific resistance and delayed-type hypersensitivity (DTH) in immunity to tuberculosis has long been a topic of debate. Here, Ian Orme and Andrea Cooper propose that the events are separate mechanisms; protection is cytokine driven and initially controls the infection, whereas DTH is primarily chemokine driven and functions to wall off the infection and prevent further dissemination.

Human gamma delta T cells recognize alkylamines derived from microbes, edible plants, and tea: implications for innate immunity

Approximately 4% of peripheral blood T cells in humans express a T cell receptor with markedly restricted germline gene segment usage (V gamma 2 V delta 2). Remarkably, these T cells expand 2- to 10-fold (8%-60% of all circulating T cells) during many microbial infections. We show here that these T cells recognize a family of naturally occurring primary alkylamines in a TCR-dependent manner. These antigenic alkylamines are secreted to millimolar concentrations in bacterial supernatants and are found in certain edible plants. Given the large numbers of memory V gamma 2 V delta 2 T cells in adult humans, recognition of alkylamine antigens offers the immune system a response of the magnitude of major superantigens for alpha beta T cells and may bridge the gap between innate and adaptive immunity.

Immunological defense mechanisms in tuberculosis and MAC-infection

Protective immunity to mycobacterial infections develops in immunocompetent hosts after activation of alpha beta- and gamma delta-T cells in association with the generation of a protection-specific cytokine profile that stimulates the bactericidal potential of the macrophages. The maintenance of a delicate balance between Th1 and Th2 response is decisive for infection control and prevention of exacerbation of disease. Mycobacterial infection in the immunocompromised host is mainly due to the diminished cellular immune function. In addition, nontuberculous mycobacteria isolated from AIDS patients have special virulence factors that promote development of disease by further compromising the function of an already damaged cytokine network.

Corynebacterium parvum- and Mycobacterium bovis Bacillus Calmette and Guerin-induced granuloma formation in mice lacking CD4 and CD8

Granuloma formation is a T-cell-dependent inflammatory response that is important in the host defense against intracellular bacteria. The role of CD4 and CD8 molecules in the development of Corynebacterium parvum- and Mycobacterium bovis Bacillus Calmette and Guerin (BCG)-induced granulomas was examined in CD4/CD8 knockout (KO) mice. CD4/CD8 KO mice developed a greater granulomatous response to heat-killed C. parvum and heat-killed BCG than did control mice. Thus, granuloma formation is not dependent upon the presence of CD4 and CD8. On the other hand, CD4/CD8 KO mice challenged with live BCG showed initially fewer and smaller granulomas but later more and larger granulomas than control mice. CD4/CD8 KO mice had a greater BCG load than control mice. The absence of CD4 and CD8 therefore impaired the host defense against infection with BCG. alphabeta T-cells were present in the granulomas of both CD4/CD8 KO and control mice in similar numbers. Also the production of IFN-gamma mRNA was similar in the two groups. In conclusion, CD4 and CD8 are not essential to the granulomatous response against C. parvum and BCG, but contribute to the host defense against live BCG infection.

Cutting Edge: Protective Response to Pulmonary Injury Requires γδ T Lymphocytes

γδ intraepithelial lymphocytes are thought to coordinate responses to pathogens that penetrate the epithelial barrier. To directly test this, mice were inoculated with Nocardia asteroides. At doses that were nonlethal for control mice, γδ-deficient mice became severely ill and died within 14 days. Histologic examination of these lungs demonstrated the presence of severe tissue damage and unimpeded bacterial growth in the γδ-deficient mice compared with neutrophilic lesions and clearance of the organism in control mice. Interestingly, ozone exposure that targets a comparable lung region also resulted in diffuse epithelial necrosis associated with a similar lack of neutrophil recruitment in γδ-deficient mice. These data demonstrate that γδ intraepithelial lymphocytes can protect the host from pathogenic and nonpathogenic insults by targeting the inflammatory response to epithelial necrosis.

Comparison of the roles of reactive oxygen and nitrogen intermediates in the host response to Mycobacterium tuberculosis using transgenic mice

OBJECTIVE

To study the role of reactive oxygen intermediates (ROI) and reactive nitrogen intermediates (RNI) in host response to Mycobacterium tuberculosis.

DESIGN

M. tuberculosis infection (i.v.) was compared in B6 control and two strains of knockout (KO) mice. X-CGD mice with a nonfunctional allele for the gp91phox subunit of the phagocyte oxidase cytochrome b are unable to produce ROI whereas iNOS KO mice lack a functional inducible nitric oxide synthase (iNOS) gene and fail to make RNI.

RESULTS

M. tuberculosis growth was markedly enhanced in the lungs of X-CGD mice compared to B6 mice, but was controlled in the spleen and liver. In iNOS KO mice, M. tuberculosis growth was exacerbated in the spleen, but was unremarkable in the lungs compared to B6 mice until later (Day 60) in the infection. In vitro, X-CGD alveolar and peritoneal macrophages (M phi) produced no ROI, but did produce RNI and inhibited growth of M. tuberculosis when activated with interferon gamma. iNOS KO M phi produced ROI, but failed to produce RNI and could not cope with M. tuberculosis in vitro when activated. The inhibition of M. tuberculosis growth observed in activated B6 and X-CGD M phi) was reversed in the presence of aminoguanidine.

CONCLUSION

These KO mouse strains demonstrate the relative potent effects of ROI and RNI in resistance to M. tuberculosis and should prove useful for the study of regulatory and compensatory mechanisms of immunity.

Gammadelta T cells and Mycobacterium tuberculosis

Since the first descriptions of mycobacterial reactivity for gammadelta T cells in 1989, studies of gammadelta T-cell responses to M. tuberculosis in humans and animal models have increased our understanding of the complex role(s) of this T-cell subset not only in the immune response to M. tuberculosis, but also to microbial pathogens in general. Although CD4+ T cells remain the dominant and critical T-cell subset in protection against M. tuberculosis, gammadelta T cells appear to have an important complementary role, which may be primarily expressed in and around maturing granulomas. This is a difficult area to study in humans. Gammadelta T cells are potent sources of IFN-gamma and competent cytotoxic effector cells, but differ from CD4+ T cells in the antigens they recognize and the manner in which M. tuberculosis-infected macrophages process and present antigens to these two subsets. One of the most fascinating features of Vgamma9/Vgamma2+ gammadelta T cells is their responsiveness to non-peptidic molecules. Solving the mechanism(s) of antigen recognition and presentation of these molecules to gammadelta T cells should help determine whether gammadelta T cells are responding to universal 'supernatigen'-like motifs expressed by a broad range of microbes or in fact discriminate among a diversity of peptidic and nonpeptidic microbial antigens. Enhanced understanding of the function of and antigen recognition by Vgamma9+/Vgamma2+ T cells is not only important for immunity to M. tuberculosis but also for T-cell responses to microbial pathogens in general.

New vaccines against tuberculosis. The status of current research

The increasing realization that the current vaccine for tuberculosis, bacille Calmette-Guérin (BCG), is of varying effectiveness, and is less protective in adults than in children, has prompted new research for a replacement. New research has resulted in innovative approaches, including the use of sub-unit vaccines, auxotropic vaccines, DNA vaccines, and recombinant vaccines, among others. This article reviews these approaches and test results in animal models, and discusses their potential for use in humans.

T cell mediated immunity to Mycobacterium tuberculosis

Recent advances in the characterization of the protective immune response to mycobacteria have highlighted the central role of phenotypically and functionally distinct subsets of T cells. These T cell subsets not only contribute to host defense by the secretion of macrophage-activating cytokines, but also by lysing the host cell. Besides releasing intracellular pathogens, which can then be taken up and killed by newly recruited macrophages, it has now been demonstrated that lysis of infected targets by one subset of cytolytic T cells can directly kill Mycobacterium tuberculosis.

Regulation by cytokines (IL-12, IL-15, IL-4 and IL-10) of the Vgamma9Vdelta2 T cell response to mycobacterial phosphoantigens in responder and anergic HIV-infected persons

Human Vgamma9Vdelta2 T cells contribute to immunity against intracellular pathogens and recognize nonpeptidic antigens, such as the mycobacterial phosphoantigen TUBAg. HIV infection is associated with a polyclonal decrease of peripheral Vgamma9Vdelta2 T cells and we previously reported that the remaining cells show a proliferative anergy to stimulation with Mycobacterium tuberculosis in 60% of patients. Because of alterations in the Th1/Th2 cytokine balance reported in HIV infection, we analyzed, at the single-cell level, the influence of exogenous IL-4, IL-10, IL-12 and IL-15 on the response to mycobacterial phosphoantigens of gammadelta T cells from HIV-infected patients and healthy donors. We report that the strong gammadelta T cell response to TUBAg is characterized by the rapid and selective production of the Th1/proinflammatory cytokines IFN-gamma and TNF-alpha in responder HIV-infected donors. In addition, a positive regulation by IL-12 and IL-15 of the production of these cytokines by Vgamma9Vdelta2 T cells in response to nonpeptidic ligands was observed, whereas IL-4 and IL-10 had no effect. In contrast, Vgamma9Vdelta2 T cells from the anergic HIV-infected donors had lost the ability to produce Th1 cytokines and were not shifted towards a Th2 profile. Furthermore, neither IL-12 nor IL-15 could reverse this functional anergy. The consequences of these observations are discussed in the context of HIV pathogenesis.

Role of heat shock proteins in protection from and pathogenesis of infectious diseases

Increased synthesis of heat shock proteins (hsp) occurs in prokaryotic and eukaryotic cells when they are exposed to stress. By increasing their hsp content, cells protect themselves from lethal assaults, primarily because hsp interfere with the uncontrolled protein unfolding that occurs under stress. However, hsp are not produced only by stressed cells; some hsp are synthesized constitutively and perform important housekeeping functions. Accordingly, hsp are involved in the assembly of molecules which play important roles in the immune system. It is not surprising that due to their wide distribution and their homology among different species, hsp represent target antigens of the immune response. Frequent confrontation of the immune system with conserved regions of hsp which are shared by various microbial pathogens can potentiate antimicrobial immunity. However, long-term confrontation of the immune system with hsp antigens which are similar in the host and invaders may convert the immune response against these host antigens and promote autoimmune disease. This review provides an overview of the role of hsp in immunity with a focus on infectious and autoimmune diseases.

Lyme Arthritis Synovial γδ T Cells Respond to Borrelia burgdorferi Lipoproteins and Lipidated Hexapeptides

Lyme arthritis synovial fluid contains a large proportion of γδ T cells that proliferates upon stimulation with the causative spirochete, Borrelia burgdorferi. A panel of Borrelia-reactive γδ T cell clones was derived from synovial fluid of two patients with Lyme arthritis. Each of six γδ clones from one patient used the Vδ1 TCR segment but had otherwise unique CDR3 sequences and diverse Vγ segment usage. Stimulation of the Vδ1 clones was optimal in the presence of Borrelia, dendritic cells, and exogenous IL-2, which was reflected by proliferation, TCR down-modulation, as well as induction of CD25 and Fas ligand expression. Stimulation by B. burgdorferi-pulsed dendritic cells withstood chemical fixation and was not restricted to class I or class II MHC, CD1a, CD1b, or CD1c. In contrast, anti-γδ antibody potently inhibited proliferation. Extraction of B. burgdorferi lipoproteins with Triton X-114 enriched for the stimulatory component. This was confirmed using lipidated vs nonlipidated hexapeptides of Borrelia outer surface proteins. These observations suggest that synovial Vδ1 T cells may mediate an innate immune response to common lipoprotein products of spirochetes.

Prostaglandin E2 Protects Against Liver Injury After Escherichia coli Infection but Hampers the Resolution of the Infection in Mice

cAMP-increasing agents such as prostaglandin E2 (PGE2) are known to protect against LPS-induced liver injury by down-regulating the production of inflammatory cytokines such as TNF-α. However, the effects of such reagents on host defense against bacterial infection remain unknown. We show here that in vivo administration of PGE2 significantly protected mice against liver injury after Escherichia coli infection but hampered the resolution of the infection. PGE2 significantly suppressed circulating TNF-α and IL-12 levels but increased the IL-10 production after E. coli challenge. PGE2 inhibited the emergence of γδ T cells in the peritoneal cavity, which are important for host defense against E. coli, and deteriorated bacterial exclusion in the peritoneal cavity after E. coli challenge. These results suggested that PGE2 affects host defense mechanisms against E. coli infection through modulation of cytokine production and γδ T cell accumulation.

Analysis of T cells recruited during delayed-type hypersensitivity to purified protein derivative (PPD) versus challenge with tuberculosis infection

The delayed-type hypersensitivity (DTH) to purified protein derivative (PPD) test has been used to infer about protective immunity to Mycobacterium tuberculosis and to diagnose tuberculosis. We showed that in memory tuberculosis-immune mice both DTH to PPD and resistance to M. tuberculosis could be effectively elicited in the footpad and both reactions led to the accumulation of reactive T cells in the regional lymph nodes with a CD4+ phenotype and characterized by the secretion of high levels of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) and no IL-4. By adoptive transfer into nude mice of highly purified CD4+ T cells harvested during the recall of protective immunity it was confirmed that this population mediated both manifestations. However, the specificity of the T cells recruited during these processes were found to differ markedly; T cells involved in protection to a challenge with live tuberculosis bacilli recognized predominantly low-mass culture filtrate antigens below 15 000 MW, while cells recruited during DTH to PPD were directed to molecular mass fractions between 15 000 and 31 000. Using single purified antigens we showed that the latter cells recognized the secreted mycobacterial protein Ag85B and the heat-shock proteins, DnaK and GroEL. Protective T cells, in contrast, were characterized by a very high frequency of T cells directed to the ESAT-6 peptide 1-20.

Isolation and characterisation of T lymphocytes from the urethra of patients with acute urethritis

OBJECTIVES

To investigate local cellular immune responses in patients with acute urethritis.

METHODS

We have established T cell lines from the urethral exudate and examined their phenotype by flow cytometry. As controls, T cell lines were cultured from first pass urine specimens of asymptomatic healthy individuals.

RESULTS

Using interleukin 2 (IL-2) alone a T cell line was obtained on only one occasion. Following culture with IL-2, and subsequent expansion by a single stimulation with irradiated allogenic peripheral blood mononuclear cells (PBMC), phytohaemagglutinin (PHA), and IL-2, it was possible to establish T cell lines from 6/6 acute urethritis patients. T cell lines were also obtained from 4/12 controls subjects, but required repetitive rounds of stimulation with mitogen and allogeneic PBMC to produce sufficient cell numbers for analysis. Three of the patient T cell lines were dominated by T cells expressing the gamma delta receptor.

CONCLUSION

The gamma delta T cell subset has been associated with immune responses at mucosal surfaces and has the ability to recognise certain bacterial antigens. The gamma delta T cell response may represent an important aspect of the immune response to organisms associated with acute urethritis.

Protective roles of gamma delta T cells and interleukin-15 in Escherichia coli infection in mice

The number of gamma delta T cells in the peritoneal cavity was increased after an intraperitoneal (i.p.) infection with Escherichia coli in lipopolysaccharide (LPS)-responsive C3H/HeN mice but not in LPS-hyporesponsive C3H/HeJ mice. The gamma delta T cells preferentially expressed invariant Vgamma6 and Vdelta1 chains and proliferated to produce a large amount of gamma interferon in the presence of LPS. Mice depleted of gamma delta T cells by T-cell receptor delta gene mutation showed impaired resistance against E. coli as assessed by bacterial growth. Macrophages from C3H/HeN mice infected with E. coli expressed higher levels of interleukin-15 (IL-15) mRNA than those from the infected C3H/HeJ mice. Administration of anti-IL-15 monoclonal antibody inhibited, albeit partially, the appearance of gamma delta T cells in C3H/HeN mice after E. coli infection and diminished the host defense against the infection. These results suggest that LPS-stimulated gamma delta T cells play an important role in the host defense against E. coli infection and that IL-15 may be partly involved in the protection via an increase in the gamma delta T cells.

Mycobacterium tuberculosis exploits the CD95/CD95 ligand system of gammadelta T cells to cause apoptosis

Vgamma9/Vdelta2+ T cells specifically recognize Mycobacterium tuberculosis in vitro and are precociously recruited in early mycobacterial lesions. Even if gammadelta T cells are only fortuitously detected in granulomas or bronchoalveolar lavages of patients with active pulmonary tuberculosis, a role in shaping the mature alphabeta T cell response against M. tuberculosis is substantiated. Here we provide a molecular explanation for this paradox: the engagement of the gammadelta TCR by mycobacterial antigens induced the expression of CD95 ligand (CD95L) by chronically activated CD95+/CD95L- gammadelta T lymphocytes. The receptor was functional, as CD95/CD95L interaction triggered the bystander death of CD95+ cells by apoptosis. Cell death was abolished by CD95-blocking antibodies. The transient accumulation at the site of infection of CD95L+ gammadelta lymphocytes, capable of interacting with CD95+ leukocytes attracted by the response towards the pathogen, may determine the characteristics of the ensuing granulomatous disease.

Gammadelta+ and CD4+ alphabeta+ human T cell subset responses upon stimulation with various Mycobacterium tuberculosis soluble extracts

By using a flow cytometric technique which allows direct identification of proliferating cells within mixed cell populations, we have previously described that soluble extracts obtained from Mycobacterium tuberculosis or M. avium represent strong stimuli for human gammadelta+ T cells. In the present study, we demonstrate that the protocol used for the preparation of M. tuberculosis soluble extracts may have an impact on their gammadelta+ T cell stimulatory capacity. In agreement with our previous data, soluble extracts prepared from bacteria killed at 85 degrees C and directly disrupted by prolonged sonication (TBe), elicited a strong proliferation of gammadelta+ T cells after 6-7 days of stimulation. In contrast, when soluble extracts were obtained from bacteria autoclaved (121 degrees C, 25 min) and then washed by centrifugation, a predominant proportion of CD4+ alphabeta+ T cells was achieved in the responding population. The stimulatory activity for gammadelta+ T cells was recovered in the supernatant of the autoclaved bacteria, indicating that autoclaving of M. tuberculosis bacilli releases an antigen(s) into the supernatant which stimulates human gammadelta+ T cells. While protease digestion of TBe only partially reduced its stimulatory capacity on gammadelta+ T cells, the stimulatory component(s) released into the supernatant after autoclavation of bacilli was found to be sensitive to protease digestion. Interestingly, in contrast to the preponderant proportion of gammadelta+ T cells induced in the responding population by unfractionated TBe, when the extract was fractionated by fast performance liquid chromatography (FPLC), most of the fractions exhibited a strong stimulatory capacity on CD4+ alphabeta+ T cells only. The gammadelta+ T cell stimulatory activity was confined to the low molecular weight range FPLC fractions. Such results may suggest a possible regulatory role of gammadelta+ T cells on CD4+ alphabeta+ T cells.

Identification of epitopes of fibronectin attachment protein (FAP-A) of Mycobacterium avium which stimulate strong T-cell responses in mice

The T-cell response to fibronectin attachment protein (FAP-A) in BALB/c and B10.BR mice was examined. Both strains developed strong T-cell responses to FAP-A, directed to single, unique epitopes. T cells from mice infected with Mycobacterium avium responded to FAP-A, suggesting a possible role in a protective immune response.

Gammadelta T cells in host defense and epithelial cell biology

Recent studies have demonstrated increased numbers of gammadelta T cells in a variety of human infectious as well as noninfectious diseases. In some cases gammadelta T cells could be shown to destroy infected or transformed cells. Advances in the identification of ligands recognized by gammadelta T cells and the development of animal model systems to study these cells in vivo should overcome some of the major obstacles currently preventing a better understanding of gammadelta T cell function in immune responses. As we gain this knowledge it may become possible to design therapeutic strategies exploiting unique properties of gammadelta T cells to promote more effective immunity.

The surface epithelium of recurrent infected palatine tonsils is rich in gammadelta T cells

Using a large panel of MoAbs in quantitative morphometric analysis of immunohistochemically stained tissue sections, we compared the frequency and distribution of immune cells in palatine tonsils from patients with recurrent tonsillitis (RT) and patients with idiopathic tonsillar hypertrophy (ITH). We found that differences between the two patient groups in leucocyte populations were limited to the surface epithelium, whereas the cellular composition of interfollicular and follicular areas was similar. Most intraepithelial lymphocytes were CD8+ T cells in both groups. However, the number of intraepithelial T cells was significantly higher in RT compared with ITH. This was due to a selective increase in the number of intraepithelial CD8+ gammadelta T cells utilizing Vdelta1 and Vgamma9. In both patient groups the majority of the intraepithelial gammadelta T cells expressed Vdelta1 and Vgamma9. Subepithelially, gammadelta T cells utilizing Vgamma9 dominated over cells utilizing Vgamma8, while equal proportions expressed Vdelta1 and Vdelta2. These results suggest that cells utilizing the otherwise rare combination Vdelta1/Vgamma9 in their T cell receptors (TCR) may constitute a major gammadelta T cell population in palatine tonsils and are probably reactive to antigens specific to the tonsillar milieu. Furthermore, they indicate that preferentially this gammadelta T cell subpopulation is involved in immune reactions within the surface epithelium in RT. We speculate that gammadelta T cells are involved in clearing infectious bacteria at the tonsillar surface and in limiting inflammatory responses in the tonsils. Both local expansion and infiltration of blood cells probably contribute to the high numbers of gammadelta T cells in RT patients.

Processing of Mycobacterium tuberculosis bacilli by human monocytes for CD4+ alphabeta and gammadelta T cells: role of particulate antigen

Mycobacterium tuberculosis readily activates both CD4+ and Vdelta2+ gammadelta T cells. Despite similarity in function, these T-cell subsets differ in the antigens they recognize and the manners in which these antigens are presented by M. tuberculosis-infected monocytes. We investigated mechanisms of antigen processing of M. tuberculosis antigens to human CD4 and gammadelta T cells by monocytes. Initial uptake of M. tuberculosis bacilli and subsequent processing were required for efficient presentation not only to CD4 T cells but also to Vdelta2+ gammadelta T cells. For gammadelta T cells, recognition of M. tuberculosis-infected monocytes was dependent on Vdelta2+ T-cell-receptor expression. Recognition of M. tuberculosis antigens by CD4+ T cells was restricted by the class II major histocompatibility complex molecule HLA-DR. Processing of M. tuberculosis bacilli for Vdelta2+ gammadelta T cells was inhibitable by Brefeldin A, whereas processing of soluble mycobacterial antigens for gammadelta T cells was not sensitive to Brefeldin A. Processing of M. tuberculosis bacilli for CD4+ T cells was unaffected by Brefeldin A. Lysosomotropic agents such as chloroquine and ammonium chloride did not affect the processing of M. tuberculosis bacilli for CD4+ and gammadelta T cells. In contrast, both inhibitors blocked processing of soluble mycobacterial antigens for CD4+ T cells. Chloroquine and ammonium chloride insensitivity of processing of M. tuberculosis bacilli was not dependent on the viability of the bacteria, since processing of both formaldehyde-fixed dead bacteria and mycobacterial antigens covalently coupled to latex beads was chloroquine insensitive. Thus, the manner in which mycobacterial antigens were taken up by monocytes (particulate versus soluble) influenced the antigen processing pathway for CD4+ and gammadelta T cells.

Identification and characterization of protective T cells in hsp65 DNA-vaccinated and Mycobacterium tuberculosis-infected mice

Immunization by intramuscular injection of plasmid DNA expressing mycobacterial 65-kDa heat shock protein (hsp65) protects mice against challenge with virulent Mycobacterium tuberculosis H37Rv. During infection or after immunization, CD4+/CD8- and CD8+/CD4- hsp65-reactive T cells increased equally in spleens. During infection, the majority of these cells were weakly CD44 positive (CD44(lo)) and produced interleukin 4 (IL-4) whereas after immunization the majority were highly CD44 positive (CD44(hi)) and produced gamma interferon (IFN-gamma). In adoptive transfer of protection to naive mice, the total CD8+/CD4- cell population purified from spleens of immunized mice was more protective than that from infected mice. When the cells were separated into CD4+/CD8- and CD8+/CD4- types and then into CD44(hi) and CD44(lo) types, CD44(lo) cells were essentially unable to transfer protection, the most protective CD44(hi) cells were CD8+/CD4-, and those from immunized mice were much more protective than those from infected mice. Thus, whereas the CD44(lo) IL-4-producing phenotype prevailed during infection, protection was associated with the CD8+/CD44(hi) IFN-gamma-producing phenotype that predominated after immunization. This conclusion was confirmed and extended by analysis of 16 hsp65-reactive T-cell clones from infected mice and 16 from immunized mice; the most protective clones, in addition, displayed antigen-specific cytotoxicity.

Lethal tuberculosis in interleukin-6-deficient mutant mice

Tuberculosis is a chronic infectious disease which causes major health problems globally. Acquired resistance is mediated by T lymphocytes and executed by activated macrophages. In vitro studies have emphasized the importance of macrophage activation for mycobacterial growth inhibition. In vivo, the protective host response is focused on granulomatous lesions in which Mycobacterium tuberculosis is contained. A cellular immune response of the T helper 1 (Th1) type is considered central for control of tuberculosis. Using interleukin-6 (IL-6)-deficient mice, we here demonstrate a crucial role of this pluripotent cytokine in protection against M. tuberculosis but not against Mycobacterium bovis BCG. Infection with M. tuberculosis was lethal for the IL-6-deficient mice at inocula that were still controlled by IL-6-competent mice. Spleen cells from M. tuberculosis-infected IL-6-/- mouse mutants produced elevated levels of IL-4 and reduced levels of gamma interferon compared to the control levels. Cytofluorometric analyses of spleen cells from M. tuberculosis-infected mice revealed more-profound alterations in T-cell ratios in IL-6-/- mice than in control mice. We assume that IL-6 contributes to host resistance by its proinflammatory activity and by its influence on cytokine secretion.