Apoptosis of Th1-like cells in experimental tuberculosis (TB)

Sheep vaccinated against paratuberculosis have increased levels of B cells infiltrating the intestinal tissue

Systemic immunisation delivered subcutaneously is currently used to control paratuberculosis, a chronic enteritis of ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP). These vaccines do not provide complete protection and a small cohort of animals still succumb to clinical disease. The aim of this study was to assess mycobacterial infection site-specific variations in immune cells in vaccinated sheep that did or did not develop the disease following controlled exposure to MAP. Immunohistochemical staining of terminal ileum demonstrated that vaccination increased infiltration of CD4 + T cells and B cells. Infiltration of large numbers of CD4 + T and B cells was also seen in sheep that successfully cleared infection. Vaccination promoted the polarisation of macrophages to an M1 activation state. The presence of certain cells at the site of infection, especially CD4 + T cells, is likely to contribute to vaccine success by increasing the speed and potency of the local immune response. Systemic immunisation against MAP can alter the composition of innate and adaptive immune cell populations at the predilection site for MAP infection in the ileum one year after vaccination. This informs understanding of the impact of vaccination at the site of infection and also the duration of vaccine-elicited changes. This information may assist vaccine development and allow targeting of protective immune responses in the gut of ruminants.

Successful Cord Blood Transplantation for Idiopathic CD4+ Lymphocytopenia

Idiopathic CD4+ lymphocytopenia (ICL) is the depletion of CD4+ lymphocytes to <300 cells/mm3 without human immunodeficiency virus infection or other causes of lymphocytopenia. ICL causes fatal infections; its etiology remains unclear and it lacks consensus regarding therapeutic options. We report the first patient with ICL who had a successful clinical course following a cord blood transplant (CBT). A 45-year-old woman was diagnosed with ICL and underwent partial hepatectomy for an abscess caused by the Mycobacterium avium complex. No specific gene alterations were detected through next generation sequencing-based evaluation. Following a reduced-intensity conditioning (RIC) regimen consisting of fludarabine, busulfan, and 4 Gy total body irradiation, a single-unit CBT was performed. Neutrophils were engrafted on day +14. CD4+ lymphocyte counts increased to over 300 cells/mm3 on day +436. After 75 months, she was alive without any sequelae. CBT with an RIC regimen could be a curable treatment option for ICL.

Cell death at the cross roads of host-pathogen interaction in Mycobacterium tuberculosis infection

Tuberculosis (TB) continues to be the leading cause of death by any single infectious agent, accounting for around 1.7 million annual deaths globally, despite several interventions and support programs by national and international agencies. With the development of drug resistance in Mycobacterium tuberculosis (M. tb), there has been a paradigm shift in TB research towards host-directed therapy. The potential targets include the interactions between host and bacterial proteins that are crucial for pathogenesis. Hence, collective efforts are being made to understand the molecular details of host-pathogen interaction for possible translation into host-directed therapy. The present review focuses on 'host cell death modalities' of host-pathogen interaction, which play a crucial role in determining the outcome of TB disease progression. Several cell death modalities that occur in response to mycobacterial infection have been identified in human macrophages either as host defences for bacterial clearance or as pathogen strategies for multiplication and dissemination. These cell death modalities include apoptosis, necrosis, pyroptosis, necroptosis, pyronecrosis, NETosis, and autophagy. These processes are highly overlapping with several mycobacterial proteins participating in more than one cell death pathway. Until now, reviews in M. tb and host cell death have discussed either focusing on host evasion strategies, apoptosis, autophagy, and necrosis or describing all these forms with limited discussions of their role in host-pathogen interactions. Here, we present a comprehensive review of various mycobacterial factors modulating host cell death pathways and the cross-talk between them. Besides this, we have discussed the networking of host cell death pathways including the interference of host miRNA during M. tb infection with their respective targets. Through this review, we present the host targets that overlap across several cell death modalities and the technical limitations of methodology in cell death research. Given the compelling need to discover alternative drug target(s), this review identifies these overlapping cell death factors as potential targets for host-directed therapy.

Diametric Role of the Latency-Associated Protein Acr1 of Mycobacterium tuberculosis in Modulating the Functionality of Pre- and Post-maturational Stages of Dendritic Cells

It is instrumental for the Mycobacterium tuberculosis (Mtb) to persist within its host in dormancy. Mtb represses most of its metabolic machinery during latency, but upregulates the expression of latency-associated protein alpha-crystallin protein (Acr1). Therefore, it is imperative to understand how throughout dormancy, Mtb employs Acr1 to regulate the host immunity. This study reveals that Acr1 exhibits divergent effect on the pre- and post-maturation stages of dendritic cells (DCs). In the current study, we demonstrate that early encounter of bone marrow cells with Acr1 while differentiating into DCs (AcrDC^pre), leads to impairment in their maturation. In contrast, when exposed to Acr1 after maturation (AcrDC^post), DCs show augmentation in their activity, secretion of TNF-α, IL-12, IL-6, and activation of T cells. Additionally, AcrDC^post promoted the polarization of naïve CD4 T cells to Th1 cells and Th17 cells and restricted the intracellular growth of Mtb. Furthermore, these DCs upregulated the expression of CCR7 and exhibited enhanced migratory capabilities. The discrete impact of Acr1 on DCs is mediated through a mechanism involving STAT-1, SOCS-3, ERK, TLR-4, and NF-κB signaling pathways. This study reveals the unprecedented role of Acr1 in distinctly modulating the function of DCs at different stages of maturation.

Blockade of the Kv1.3 K+ Channel Enhances BCG Vaccine Efficacy by Expanding Central Memory T Lymphocytes

Tuberculosis is the oldest known infectious disease, yet there is no effective vaccine against adult pulmonary tuberculosis. Emerging evidence indicates that T-helper 1 and T-helper 17 cells play important roles in host protection against tuberculosis. However, tuberculosis vaccine efficacy in mice is critically dependent on the balance between antigen-specific central memory T (Tcm) and effector memory T (Tem) cells. Specifically, a high Tcm/Tem cell ratio is essential for optimal vaccine efficacy. Here, we show that inhibition of Kv1.3, a potassium channel preferentially expressed by Tem cells, by Clofazimine selectively expands Tcm cells during BCG vaccination. Furthermore, mice that received clofazimine after BCG vaccination exhibited significantly enhanced resistance against tuberculosis. This superior activity against tuberculosis could be adoptively transferred to naive, syngeneic mice by CD4⁺ T cells. Therefore, clofazimine enhances Tcm cell expansion, which in turn provides improved vaccine efficacy. Thus, Kv1.3 blockade is a promising approach for enhancing the efficacy of the BCG vaccine in humans.

An Intracellular Arrangement of Histoplasma capsulatum Yeast-Aggregates Generates Nuclear Damage to the Cultured Murine Alveolar Macrophages

Histoplasma capsulatum is responsible for a human systemic mycosis that primarily affects lung tissue. Macrophages are the major effector cells in humans that respond to the fungus, and the development of respiratory disease depends on the ability of Histoplasma yeast cells to survive and replicate within alveolar macrophages. Therefore, the interaction between macrophages and H. capsulatum is a decisive step in the yeast dissemination into host tissues. Although the role played by components of cell-mediated immunity in the host's defense system and the mechanisms used by the pathogen to evade the host immune response are well understood, knowledge regarding the effects induced by H. capsulatum in host cells at the nuclear level is limited. According to the present findings, H. capsulatum yeast cells display a unique architectural arrangement during the intracellular infection of cultured murine alveolar macrophages, characterized as a formation of aggregates that seem to surround the host cell nucleus, resembling a “crown.” This extranuclear organization of yeast-aggregates generates damage on the nucleus of the host cell, producing DNA fragmentation and inducing apoptosis, even though the yeast cells are not located inside the nucleus and do not trigger changes in nuclear proteins. The current study highlights a singular intracellular arrangement of H. capsulatum yeast near to the nucleus of infected murine alveolar macrophages that may contribute to the yeast's persistence under intracellular conditions, since this fungal pathogen may display different strategies to prevent elimination by the host's phagocytic mechanisms.

Apoptosis of lymph node and peripheral blood cells in ovine Johne's disease

Ovine Johne's disease (OJD) is a degenerative wasting condition of ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). Similar to other pathogenic mycobacterial infections it is a slow-progressing chronic disease and subclinically infected individuals can spread the disease while appearing healthy. MAP infects macrophages and the host responds by mounting a cell-mediated immune response. Disease progression is associated with immune dysfunction but the reasons are unknown. Increasing our current knowledge of the immunological mechanisms involved in disease progression, including apoptotic responses, may allow advancements in the area of early diagnosis, identification of resistant animals and disease control. We describe lymphocyte apoptosis in peripheral blood mononuclear cells (PBMC) and lymph node cells from sheep exposed to MAP as well as from healthy non-exposed sheep. Apoptosis in intestinal lymph node cells from MAP-exposed infected sheep, but not in MAP-exposed uninfected sheep, increased in response to MAP antigen. In this first longitudinal study of lymphocyte apoptosis using an experimental infection model of MAP infection, we found that there was a transient increase of ex vivo PBMC apoptosis in MAP-exposed sheep soon after exposure to MAP (4 months post inoculation). MAP antigen-specific apoptosis occurred later, at 12 months post inoculation. The cells involved were mainly γδ and CD4(+) T cells. Antigen-mediated lymphocyte apoptosis during mycobacterial disease progression could contribute to the immune dysfunction in Johne's disease.

Deciphering the pathways of death of Histoplasma capsulatum-infected macrophages: implications for the immunopathogenesis of early infection

Apoptosis of leukocytes is known to strongly influence the immunopathogenesis of infection. In this study, we dissected the death pathways of murine macrophages (MΦs) infected with the intracellular pathogen Histoplasma capsulatum. Yeast cells caused apoptosis of MΦs at a wide range of multiplicity of infection, but smaller inocula resulted in delayed detection of apoptosis. Upon infection, caspases 3 and 1 were activated, and both contributed to cell death; however, only the former was involved in apoptosis. The principal driving force for apoptosis involved the extrinsic pathway via engagement of TNFR1 by TNF-α. Infected MΦs produced IL-10 that dampened apoptosis. The chronology of TNF-α and IL-10 release differed in vitro. The former was detected by 2 h postinfection, and the latter was not detected until 8 h postinfection. In vivo, the lungs of TNFR1(-/-) mice infected for 1 d contained fewer apoptotic MΦs than wild-type mice, whereas the lungs of IL-10(-/-) mice exhibited more. Blockade of apoptosis by a pan-caspase inhibitor or by simvastatin sharply reduced the release of TNF-α but enhanced IL-10. However, these treatments did not modify the fungal burden in vitro over 72 h. Thus, suppressing cell death modulated cytokine release but did not alter the fungal burden. These findings provide a framework for the early pathogenesis of histoplasmosis in which yeast cell invasion of lung MΦs engenders apoptosis, triggered in part in an autocrine TNF-α-dependent manner, followed by release of IL-10 that likely prevents apoptosis of newly infected neighboring phagocytes.

The death-promoting molecule tumour necrosis factor-related apoptosis inducing ligand (TRAIL) is not required for the development of peripheral lymphopenia or granuloma necrosis during infection with virulent Mycobacterium avium

Disseminated infection with virulent Mycobacterium avium in C57Bl/6 (B6) mice leads to severe lymphocyte depletion in secondary lymphoid organs. In this study, we found an up-regulation of caspase-8 activity in spleen cell extracts from M. avium 25291-infected B6 mice compared to non-infected mice. The activation of this extrinsic apoptotic pathway correlated with an increase in inter-nucleosomal DNA fragmentation in CD4(+) spleen cells, as analysed by the terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay. These data suggest the involvement of death receptors in the induction of lymphocyte loss in the spleen, but previous work has excluded a role for tumour necrosis factor (TNF) receptors and Fas/CD95 in M. avium-induced lymphopenia. TNF-related apoptosis-inducing ligand (TRAIL) is expressed by different cell types of the immune system and induces apoptosis and killing of tumour cells while sparing normal cells. Here we used TRAIL(-/-) mice to determine if the absence of TRAIL prevented M. avium-induced immune pathology. We found that TRAIL-deficient mice still developed splenic lymphopenia during disseminated infection or granuloma necrosis during low-dose infections while exhibiting slightly increased susceptibility to M. avium 25291 when compared to B6 mice. However, in vivo proliferation of less virulent strains of M. avium was not influenced by TRAIL deficiency despite a decrease in interferon-γ production in infected B6.TRAIL(-/-) mice compared to B6 mice. Our results show that TRAIL does not play a significant role in either M. avium-induced pathology or protective immunity.

Comparative evaluation of cytokines, T-cell apoptosis, and costimulatory molecule expression in tuberculous and nontuberculous pleurisy

In this study, we compared several immune parameters in tuberculosis (TB) and nontuberculosis (NTB) pleurisy to gain an understanding of the mechanism behind enhanced Th1 apoptosis that occurs at sites of active Myobacterium tuberculosis (M. tuberculosis) infection. An initial evaluation of the accumulated cytokines in pleural fluid (PF) demonstrated that both TB and NTB pleurisy were associated with prointflammatory cytokines, while only TB pleurisy had augmented expression of interferon (IFN)-gamma and soluble Fas ligand (sFASL). Despite enhanced expression of the apoptosis-inducing molecule in TB pleurisy, T cells derived from both types of pleurisy exhibited significant apoptosis. In both groups, T-cell apoptosis correlated with low expression of CD80 on PF-derived macrophages and elevated accumulation of TGF-beta in the PF. A causative correlation between TGF-beta and low CD80 expression in the two groups was established by in vitro studies demonstrating TGF-beta inhibition of CD80 upregulation in a macrophage cell line. Together, the findings allude to the possibility that activation in the absence of appropriate CD80 costimulation is the mechanism that leads to T-cell apoptosis at sites of active M. tuberculosis infection. Furthermore, the findings also indicate that T-cell apoptosis is perhaps a host regulatory mechanism to limit inflammation, rather than a pathogen-induced immune deviation.

Comprehensive gene expression profiling in lungs of mice infected with Mycobacterium tuberculosis following DNAhsp65 immunotherapy

BACKGROUND

The continued increase in tuberculosis (TB) rates and the appearance of extremely resistant Mycobacterium tuberculosis strains (XDR-TB) worldwide are some of the great problems of public health. In this context, DNA immunotherapy has been proposed as an effective alternative that could circumvent the limitations of conventional drugs. Nonetheless, the molecular events underlying these therapeutic effects are poorly understood.

METHODS

We characterized the transcriptional signature of lungs from mice infected with M. tuberculosis and treated with heat shock protein 65 as a genetic vaccine (DNAhsp65) combining microarray and real-time polymerase chain reaction analysis. The gene expression data were correlated with the histopathological analysis of lungs.

RESULTS

The differential modulation of a high number of genes allowed us to distinguish DNAhsp65-treated from nontreated animals (saline and vector-injected mice). Functional analysis of this group of genes suggests that DNAhsp65 therapy could not only boost the T helper (Th)1 immune response, but also could inhibit Th2 cytokines and regulate the intensity of inflammation through fine tuning of gene expression of various genes, including those of interleukin-17, lymphotoxin A, tumour necrosis factor-alpha, interleukin-6, transforming growth factor-beta, inducible nitric oxide synthase and Foxp3. In addition, a large number of genes and expressed sequence tags previously unrelated to DNA-therapy were identified. All these findings were well correlated with the histopathological lesions presented in the lungs.

CONCLUSIONS

The effects of DNA therapy are reflected in gene expression modulation; therefore, the genes identified as differentially expressed could be considered as transcriptional biomarkers of DNAhsp65 immunotherapy against TB. The data have important implications for achieving a better understanding of gene-based therapies.

IFN-gamma induces the erosion of preexisting CD8 T cell memory during infection with a heterologous intracellular bacterium

Memory T cells are critical for the control of intracellular pathogens and require few signals for maintenance; however, erosion of established preexisting memory CD8(+) T cells has been shown to occur during infection with heterologous viral infections. We evaluated whether this also occurs during infection with various intracellular bacteria and what mechanisms may be involved. We demonstrate that erosion of established memory is also induced during infection of mice with various intracellular bacteria, such as Listeria monocytogenes, Salmonella typhimurium, and Mycobacterium bovis (bacillus Calmette-Guérin). The extent of erosion of established CD8(+) T cell memory was dependent on the virulence of the heterologous pathogen, not persistence. Furthermore, when antibiotics were used to comprehensively eliminate the heterologous pathogen, the numbers of memory CD8(+) T cells were not restored, indicating that erosion of preexisting memory CD8(+) T cells was irreversible. Irrespective of the initial numbers of memory CD8(+) T cells, challenge with the heterologous pathogen resulted in a similar extent of erosion of memory CD8(+) T cells, suggesting that cellular competition was not responsible for erosion. After challenge with the heterologous pathogen, effector memory CD8(+) T cells were rapidly eliminated. More importantly, erosion of preexisting memory CD8(+) T cells was abrogated in the absence of IFN-gamma. These studies help reveal the paradoxical role of IFN-gamma. Although IFN-gamma promotes the control of intracellular bacterial replication during primary infection, this comes at the expense of erosion of preexisting memory CD8(+) T cells in the wake of infection with heterologous pathogens.

Vaccine Approaches to Prevent Tuberculosis

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is one of the main killers among infectious pathogens in the world and represents an important factor that sustain poverty in developing countries. Failure of the BCG vaccine to protect in endemic regions, and increasing problems with multi-drug-resistant TB calls for development of better vaccines to prevent reactivation of tuberculosis. It has been estimated that an effective post-exposure vaccine will prevent 30-40% of the TB cases. New vaccines should also prevent development of TB in HIV-infected individuals. Recent characterization of M. tuberculosis H37Rv by proteomic methods has revealed a large number of novel secreted proteins that should be investigated in mouse models for latent and slowly progressive TB. There is an important balance between control of infection and tissue destruction in TB, and M. tuberculosis has developed strategies to prevent immune-mediated sterilization. Central to this strategy is inhibition of apoptosis of macrophages. Development of novel vaccines should therefore take into consideration the effects on central markers to obtain a better picture of regulation of immunity, including FasL and Bcl-2 which are essential in regulation of apoptosis.

Regulatory role of pro-Th1 and pro-Th2 cytokines in modulating the activity of Th1 and Th2 cells when B cell and macrophages are used as antigen presenting cells

BACKGROUND

Presence of antigen presenting cells, expression of costimulatory molecules, the strength of first signal and cytokine milieu are quite important in influencing the reactivation of differentiated Th1 and Th2 cells.

RESULTS

In the present study, we have analyzed the concerted action of pro-Th1 and pro-Th2 cytokines in the presence of B cells, peritoneal and splenic macrophages as antigen presenting cells and varied concentration of first (anti-CD3 Ab) and second (B7-1 transfectant) signals on the proliferation and cytokine secretion by Th1 and Th2 cells. Interesting observations were made that IFN-gamma significantly augmented the secretion of IL-4 by Th2 cells when either B cells or splenic or peritoneal macrophages were used as APC. Further, IFN-gamma significantly inhibited the proliferation of Th1 cells only in the presence of peritoneal macrophages. We have also observed that B cells could significantly respond to cytokines to further enhance the proliferation and cytokine release by Th1 and Th2 cells. But not much effect on addition of exogenous cytokines IL-1, IL-4, IL-5, IL-12 was observed on the proliferation of Th1 and Th2 cells in the presence of macrophages. In contrast, both IFN-gamma and IL-2 significantly enhanced the production of IL-4 and IL-5 respectively, by Th2 cells in presence of B cells, splenic and peritoneal macrophages. Another important observation was that the addition of B7-1 transfectants in the cultures, which were stimulated with low dose of anti-CD3 Ab significantly, enhanced the proliferation and cytokine secretion.

CONCLUSION

This study indicates involvement of different type of APCs, cytokine milieu, dose of first and second signals in a concerted manner in the outcome of the immune response. The significance of this study is that the immunization with antigen along with costimulatory molecules may significantly reduce the dose of antigen and can generate better immune response than antigen alone.

Macrophage and T lymphocyte apoptosis during experimental pulmonary tuberculosis: their relationship to mycobacterial virulence

The kinetics of macrophage and T lymphocyte apoptosis were determined in a well-characterized mouse model of pulmonary tuberculosis, comparing strains of intermediate (H37Rv) and high virulence (Beijing strain, code 9501000). Both strains induced a high percentage of apoptotic activated macrophages at days 1 and 3 post infection, although this was twofold lower in Beijing-infected mice. Progressive pneumonia started at day 14 (Beijing) or 21 (H37Rv) post infection. Pneumonic areas contained numerous macrophages with vacuolated cytoplasm (VM). In H37Rv infection few VM were apoptotic (8.7% at day 60), and the percentage was even lower in Beijing infection (1.4% at day 28). A high percentage of VM expressed the anti-apoptotic molecule Bcl-2 (H37Rv, 83%; Beijing, 95%). Both strains induced a progressive increase of apoptotic Th1 lymphocytes, peaking at day 60 in H37Rv infection, or 28 in Beijing infection. The peak was twofold higher in the latter. VM had strong FasL immunostaining, and confocal microscopy showed numerous apoptotic Th1 cells closely associated with them, suggesting that VM might induce apoptosis of Th1 cells. These results support the hypothesis that apoptosis of macrophages is associated with protection, while apoptosis of Th1 cells favors disease progression, and is related to the virulence of the mycobacterial strain.

The pathogenesis and pathology of bovine tuberculosis with insights from studies of tuberculosis in humans and laboratory animal models

This paper reviews key insights the discipline of pathology has contributed to our understanding of bovine tuberculosis in the context of findings of studies of tuberculosis in humans and laboratory animal models. Analysis and extrapolation of data from other species have the potential to expand our understanding of the pathogenesis of the disease in cattle. The distribution of lesions in affected cattle, humans and laboratory animals illustrate the primacy of the respiratory tract as portal of infection and raise questions about the role of the upper respiratory tract surface, tonsil and dorsal lung regions in disease pathogenesis and transmission. The mechanisms behind significant pathological processes such as necrosis, apoptosis and liquefaction, occurring within lesions, are explored and their potential practical significance assessed in the context of herd disease dynamics and vaccine development. It is proposed that effective 'innate' host defences result in many animals and humans remaining disease-free and tuberculin test negative following exposure to infection. Furthermore, the concepts of latency and disease reactivation, considered significant factors in perpetuating tuberculosis in human populations, are explored in the context of the bovine disease.

Apoptosis modulates protective immunity to the pathogenic fungus Histoplasma capsulatum

Pathogen-induced apoptosis of lymphocytes is associated with increased susceptibility to infection. In this study, we determined whether apoptosis influenced host resistance to the fungus Histoplasma capsulatum. The level of apoptotic leukocytes progressively increased in the lungs of naive and immune mice during the course of H. capsulatum infection. T cells constituted the dominant apoptotic population. Apoptosis was diminished in H. capsulatum-infected gld/gld and TNF-alpha-deficient mice; concomitantly, the fungal burden exceeded that of controls. Treatment of naive and H. capsulatum-immune mice with caspase inhibitors decreased apoptosis but markedly enhanced the severity of infection. Administration of a proapoptotic dose of suramin diminished the fungal burden. The increased burden in recipients of a caspase inhibitor was associated with elevations in IL-4 and IL-10 levels. In the absence of either of these cytokines, caspase inhibition suppressed apoptosis but did not increase the fungal burden. Thus, apoptosis is a critical element of protective immunity to H. capsulatum. Production of IL-4 and IL-10 is markedly elevated when apoptosis is inhibited, and the release of these cytokines exacerbates the severity of infection.

Prolonged antigen presentation, APC-, and CD8+ T cell turnover during mycobacterial infection: comparison with Listeria monocytogenes

We expressed the CTL epitope of OVA (OVA(257-264)) in an acute (Listeria monocytogenes (LM)-OVA) and a chronic intracellular pathogen (Mycobacterium bovis (BCG)-OVA), to evaluate the kinetics of Ag presentation. LM-OVA proliferated rapidly in vivo, resulting in profound LM-OVA expansion within the first 24 h of infection, culminating in the generation of a potent CD8+ T cell response, which peaked on day 7 but underwent a rapid attrition subsequently. In contrast, BCG-OVA exhibited reduced growth in vivo, resulting in a delayed CD8+ T cell response that increased progressively with time. Relative to LM-OVA, BCG-OVA induced persistently increased numbers of apoptotic (annexin V+) CD8+ T cells. Ag presentation in vivo was evaluated by transferring Thy1.2+ carboxyfluorescein-labeled OT1 transgenic CD8+ T cells into infected Thy1.1+ congeneic recipient mice. LM-OVA induced rapid Ag presentation that was profound in magnitude, with most of the transferred cells getting activated within 4 days and resulting in a massive accumulation of activated donor CD8+ T cells. In contrast, Ag presentation induced by BCG-OVA was delayed, weaker in magnitude, which peaked around the second week of infection and declined to a low level subsequently. Increasing the dose of BCG-OVA while enhancing the magnitude of Ag presentation did not change the kinetics. Furthermore, a higher dose of BCG-OVA also accelerated the attrition of OVA(257-264)-specific CD8+ T cells. Relative to LM-OVA, the dendritic cells in BCG-OVA-infected mice were apoptotic for prolonged periods, suggesting that the rapid death of APCs may limit the magnitude of Ag presentation during chronic stages of mycobacterial infection.

Transforming growth factor-beta decreases survival of Mycobacterium bovis-activated T cells

BACKGROUND

A comprehensive understanding of the immune response induced by Mycobacterium bovis Bacille Calmette-Guérin in activation of protective T cells against tuberculosis is important to develop effective therapies to combat this disease. In this study, our experiments were designed to determine effects of transforming growth factor (TGF)-beta on M. bovis-induced T-cell activation and survival.

METHODS

Fluorescence-activated cell sorter (FACS) analysis was used for detection of apo-ptotic cells by three different methods: 1). scattered light change during early phase of apoptosis; 2). detection of hypodiploid DNA, or 3). terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) technique. Quantification of positively stained population was based on samples stained with isotype control antibodies analyzed on a FACScan.

RESULTS

TGF-beta added at initiation of culture did not alter percentage of viable cells. By contrast, TGF-beta added 72 h post-activation decreased percentage of viable cells. This effect was statistically significant (p <0.05). Furthermore, addition of anti-TGF-beta MoAb together with TGF-beta abolished the ability of this cytokine to decrease survival in post-activated human T cells. Role of TGF-beta on post-activated human T cells was further confirmed by staining apoptotic nuclei with propidium iodide, which detects late events of apoptosis, and by DNA fragmentation determined using TUNEL assay. Interestingly, TGF-beta did not promote Fas-mediated killing. Finally, TGF-beta increased apoptosis of CD4(+) T cells after mycobacterial stimulation.

CONCLUSIONS

This study indicated an important role for TGF-beta in suppression of protective immune response against M. bovis by promoting elimination of post-activated T cells. Furthermore, results showed that TGF-beta had no direct effect on M. bovis-induced up-regulation of Fas (CD95).

Cross-reactive antigen is required to prevent erosion of established T cell memory and tumor immunity: a heterologous bacterial model of attrition

Induction and maintenance of T cell memory is critical for the control of intracellular pathogens and tumors. Memory T cells seem to require few "maintenance signals," though often such studies are done in the absence of competing immune challenges. Conversely, although attrition of CD8(+) T cell memory has been characterized in heterologous viral models, this is not the case for bacterial infections. In this study, we demonstrate attrition of T cell responses to the intracellular pathogen Listeria monocytogenes (LM) following an immune challenge with a second intracellular bacterium, Mycobacterium bovis (bacillus Calmette-Guérin, BCG). Mice immunized with either LM or recombinant LM (expressing OVA; LM-OVA), develop a potent T cell memory response. This is reflected by peptide-specific CTL, IFN-gamma production, and frequency of IFN-gamma-secreting T cells to native or recombinant LM Ags. However, when the LM-infected mice are subsequently challenged with BCG, there is a marked reduction in the LM-specific T cell responses. These reductions are directly attributable to the effects on CD4(+) and CD8(+) T cells and the data are consistent with a loss of LM-specific T cells, not anergy. Attrition of the Ag (OVA)-specific T cell response is prevented when LM-OVA-immunized mice are challenged with a subsequent heterologous pathogen (BCG) expressing OVA, demonstrating memory T cell dependence on Ag. Although the reduction of the LM-specific T cell response did not impair protection against a subsequent LM rechallenge, for the first time, we show that T cell attrition can result in the reduction of Ag-specific antitumor (B16-OVA) immunity previously established with LM-OVA immunization.

Progressive bovine paratuberculosis is associated with local loss of CD4(+) T cells, increased frequency of gamma delta T cells, and related changes in T-cell function

Bovine paratuberculosis is caused by the infection of young calves with Mycobacterium avium subsp. paratuberculosis, resulting in a chronic granulomatous infection of predominantly the ileum. After an incubation period of 2 to 5 years, the disease becomes progressive in some of the chronically infected, but asymptomatic cows. This results in a protein-losing enteropathy that will ultimately be fatal. A loss of cell-mediated immune responses in symptomatic animals has been described, but no information is available concerning immune reactivity in the intestine. We sought to investigate putative disease status-associated lymphocyte subset distributions and antigen-specific functional characteristics of mononuclear cells isolated from blood, gut-associated lymphoid tissue, and the intestinal walls of 22 cows in different stages of disease and in control animals. The results demonstrated a significant decrease in CD4(+) T-cell frequency and a significant increase in TcR1-N12(+) gamma delta T-cell frequency in ileum lamina propria lymphocytes of symptomatic animals compared to the asymptomatic shedders. Immunohistology revealed that there was also an absolute decrease in the number of CD4(+) T cells in sections of the lesional ileum. Our findings also indicated that both peripheral and intestinal cell-mediated responses are decreased in symptomatic animals compared to asymptomatic animals. We conclude that the decrease in cell-mediated responses is likely related to a loss of antigen-specific CD4(+) T cells, which is most prominent in the lesional ileum from symptomatic animals, thus contributing to the progressive nature of bovine paratuberculosis.

Multiple mechanisms compensate to enhance tumor-protective CD8(+) T cell response in the long-term despite poor CD8(+) T cell priming initially: comparison between an acute versus a chronic intracellular bacterium expressing a model antigen

We evaluated CD8(+) T cell responses against the dominant CTL epitope, OVA(257-264), expressed by an acute (Listeria monocytogenes (LM) OVA) vs a chronic pathogen (Mycobacterium bovis bacillus Calmette-Guérin (BCG) OVA) to reveal the influence on CD8(+) T cell memory and consequent protection against a challenge with OVA-expressing tumor cells. Infection with lower doses of both pathogens resulted in stronger bacterial growth but weaker T cell memory indicating that memory correlates with pathogen dose but not with bacterial expansion. The CD8(+) T cell response induced by LM-OVA was helper T cell-independent and was characterized by a rapid effector response followed by a rapid, but massive, attrition. In contrast, BCG-OVA induced a delayed and weak response that was compensated for by a longer effector phase and reduced attrition. This response was partly dependent on CD4(+) T cells. CD8(+) T cell response induced by BCG-OVA, but not LM-OVA, was highly dependent on pathogen persistence to compensate for the weak initial CD8(+) T cell priming. Despite a stronger initial T cell response with LM-OVA, BCG-OVA provided more effective tumor (B16OVA) control at both local and distal sites due to the induction of a persistently activated acquired, and a more potent innate, immunity.

Immunophenotypic characterization of peripheral T lymphocytes in Mycobacterium tuberculosis infection and disease

The cellular immune response probably plays a pivotal role in determining the clinical outcome after exposure to Mycobacterium tuberculosis. We used multi-parameter flow-cytometry to evaluate the distribution of T-lymphocyte subsets during infection and disease caused by M. tuberculosis. Samples were obtained from 71 volunteers to identify the T CD4+ and CD8+ lymphocyte numbers, and the activation plus memory/naïve phenotypes, as defined by CD38, HLA-DR, CD45RA and CD27 markers. Subjects were divided into 18 healthy volunteers without detectable reaction to purified protein derivative (PPD-), 18 health care workers with a recent conversion to PPD, 20 patients with active pulmonary tuberculosis (TBC) and 15 patients with treated TBC at 6 months of therapy. By multiple-comparison analyses, the T CD4+ lymphocyte number of the TBC group was lower than the PPD- group (P < 0.05). This difference was apparently lost after treatment. The higher and the lower number of naïve T CD4+ cells was observed in the PPD- and TBC group, respectively. CD8+ T lymphocytes were also statistically different among the four groups (P = 0.0002), lower in the TBC group (P < 0.05). CD8+ T lymphocyte activation was evaluated by the CD38 and HLA-DR surface expression. The percentage distribution of these markers was statistically different between the four groups (P = 0.0055). TBC patients had a higher percentage of CD38+ cells and mean fluorescence index, suggesting an overall increase of cell activation. These results suggest that peripheral T lymphocytes reflect cellular activation during TBC, along with possible redistribution of naïve, memory/effector and late differentiated memory/effector phenotypes in the peripheral blood after infection and disease caused by M. tuberculosis.

Il-4 influences apoptosis of mycobacterium-reactive lymphocytes in the presence of TNF-alpha

T cell apoptosis is associated with defective cell-mediated effector functions in several infectious diseases. In tuberculosis, there is evidence that T cell apoptosis may be cytokine mediated, but the mechanisms are not clearly understood. Type 2 cytokines have recently been associated with disease extent in human tuberculosis, but they have not previously been linked to apoptosis in mycobacterium-reactive T cells. This study presents evidence that PBLs from healthy donors respond to sonicated Mycobacterium tuberculosis Ags with increased IL-4 gene activation, CD30 expression, and apoptosis. The changes were significantly greater than those observed when cells were stimulated with Ags from nonpathogenic Mycobacterium vaccae. A hypothesis linking these observations was tested. CD30 expression and TNF-alpha-mediated lymphocyte apoptosis were both down-regulated by inhibiting IL-4 in this model. TNFR-associated factor 2 (TRAF2) expression was down-regulated in CD30(+) cells, and addition of anti-TNF-alpha Ab significantly reduced apoptosis in the CD30(+) but not the CD30(-) population. These observations support the hypothesis that increased IL-4 expression in M. tuberculosis-activated lymphocytes promotes CD30 expression, which sensitizes the lymphocytes to TNF-alpha-mediated apoptosis via TRAF2 depletion. This may be one mechanism by which IL-4 is associated with immunopathological consequences in human tuberculosis.

Advances in the immunopathogenesis of pulmonary tuberculosis

Tuberculosis remains a global emergency because of our lack of understanding of the details of its pathogenesis. In the last 12 months there have been striking advances in the molecular genetics of the organism. Mutated strains of Mycobacterium tuberculosis have been used to study the genetic requirements for virulence and establishment of latency, and the biology of the interaction with host cells. Genes involved in lipid metabolism seem particularly important. The probable sites of latency within the host lungs have been identified by in situ polymerase chain reaction. The complex control by M. tuberculosis of apoptosis of T cells and macrophages has been somewhat clarified, and the data may suggest that M. tuberculosis causes death of a subset of T cells, while preserving some macrophages as hiding places with reduced microbicidal and antigen-presenting function. Similarly the demonstration of a very large relative increase in interleukin (IL)-4 and IL-13 expression, (together with IL-4delta2, the IL-4 splice variant), that correlates with lung damage, has been supported by data from flow cytometry and in situ hybridization, and indicates that a subversive T helper-2 (Th2) component in the response to M. tuberculosis may undermine the efficacy of immunity and contribute to immunopathology. Recently defined changes in metabolism of cortisol within the lesions may contribute to the development of the Th2 component. These findings underline the need to start testing vaccine candidates in models that mimic the situations in which bacille Calmette-Guerin fails, such as in the presence of latent infection, pre-existing Th2 responses to cross-reactive organisms, and stress.

Susceptibility to development of Mycobacterium ulcerans disease: review of possible risk factors

Mycobacterium ulcerans disease, also known as Buruli ulcer (BU), is a disease of subcutaneous fat tissue. BU is prevalent in riverine and swamp areas of the tropical zone in Africa, Asia and South America, and a few scattered foci in Australia. The mode of transmission of M. ulcerans has not been fully elucidated, but inoculation into the subcutaneous tissues probably occurs through penetrating skin trauma. BU has not been linked with HIV infection. Antimycobacterial drug treatment is ineffective, and treatment is surgical. Patients eventually develop scars and contractures, with resulting disabilities, and the disease imposes a large burden on affected populations. The incidence of BU has dramatically increased in West African countries over the last decade. There is an urgent need for research into host and environmental risk factors for BU in order to develop effective strategies to combat this disease. We review possible genetic host susceptibility factors for BU that are relevant in other mycobacterial diseases: natural resistance-associated macrophage protein-1 (NRAMP-1), HLA-DR, vitamin D3 receptor, mannose binding protein, interferon-gamma (IFN-gamma) receptor, tumour necrosis factor alpha (TNF-alpha), interleukin (IL)-1 alpha, 1 beta and their receptor antagonists; and IL-12. Schistosoma haematobium infection is highly endemic in many BU foci in West Africa, with a striking increase in transmission after river dams were constructed. This observation, and the observations from interaction of schistosomiasis and tuberculosis, have fueled our hypothesis that schistosomiasis is a risk factor for BU by driving the host immune response towards a predominantly Th-2 pattern, away from a Th-1 preponderant protection against mycobacterial infection. If the latter hypothesis is confirmed, enhanced schistosomiasis control should impact on BU.

CD95 signaling is not required for the down regulation of cellular responses to systemic Mycobacterium tuberculosis infection

There is a tendency among tuberculosis patients to have reduced cellular responses to mycobacterial antigens and this loss has been associated with apoptosis of CD4 T cells. In order to determine the role of CD95 in mediating apoptosis of antigen-specific lymphocytes in tuberculosis, mice with a mutated CD95L molecule were infected systemically with virulent Mycobacterium tuberculosis. Both control and CD95L mutant mice exhibited the expected loss of response to mycobacterial antigens, with the only difference being a slight delay in the loss of the response in the mutant mice. The limited persistence of the response in the mutant mice suggests that, while antigen-specific cellular responses do decline in mice infected with mycobacteria, this decline is not dependent upon CD95L.

Fas-FasL interaction modulates nitric oxide production in Trypanosoma cruzi-infected mice

During acute Trypanosoma cruzi infection in mice, many leucocytes undergo apoptosis. Although apoptosis has been ascribed to increased levels of nitric oxide (NO) and Fas-FasL interaction, the importance of this phenomenon in modulating the host response against T. cruzi is unknown. Herein, the role of NO- and Fas-FasL-induced apoptosis in modulating the immune response to T. cruzi was evaluated using mice deficient in Fas expression (MRL/MpJ-Fas lpr) and inducible nitric oxide synthase (iNOS) knockout mice (iNOS-/-). The results showed that besides decreasing apoptosis induction after infection, impairment of the Fas-FasL interaction resulted in decreased NO production, as a consequence of enhanced T helper 2 (Th2) cytokine production. Differently, blockage of NO-induced apoptosis resulted in uncontrolled cytokine production, rather than a biased Th2 cytokine pattern. Together, these results suggested that Fas and FasL-induced apoptosis could be implied in modulation of the immune response against T. cruzi by interfering with cytokine and NO production during the acute phase of the infection.

Differential changes in heat shock protein-, lipoarabinomannan-, and purified protein derivative-specific immunoglobulin G1 and G2 isotype responses during bovine Mycobacterium avium subsp. paratuberculosis infection

Bovine paratuberculosis is caused by infection of young calves with Mycobacterium avium subsp. paratuberculosis. In some of the chronically infected cows the long asymptomatic stage (2 to 4 years) is followed by a rapid progression to a clinical stage due to protein-losing enteropathy, which will ultimately be fatal. The current dogma is that in early stages of disease the cell-mediated responses predominate, whereas in the clinical stage of the disease the humoral responses prevail, possibly signaling a switch in immune reactivity related to disease progression. We developed immunoglobulin M (IgM)-, IgA-, and IgG1- and IgG2-isotype-specific enzyme-linked immunosorbent assays for M. avium subsp. paratuberculosis-derived antigens (heat shock proteins of 70 kDa [Hsp70] and 65 kDa [Hsp65], lipoarabinomannan [LAM], and M. avium subsp. paratuberculosis purified protein derivative PPD [PPDP]). The serological responses of cows in different stages of paratuberculosis were used to evaluate the putative shift in immune responsiveness. In the clinical stage the PPDP-specific IgG1 responses were increased compared to those in the asymptomatic stage. However, total IgG1 and IgG2 and the Hsp70-, Hsp65-, and LAM-specific isotype responses were decreased in the clinical stage were decreased compared to those in the asymptomatic stage of disease. Thus, the classical pattern was found only for PPDP antigens and the IgG1 isotype. For other antigens and isotypes and the total IgG levels, the response pattern is different and indicates that there is no uniform association with increased antibody responses during the progression from the asymptomatic stage to the clinical stage of bovine paratuberculosis.

M. tuberculosis: immunology and vaccination

Tuberculosis is increasing. Current treatment regimens require at least 6 months, because latent or stationary phase organisms are difficult to kill. Such regimens do not achieve full compliance, and "directly observed therapy short course" (DOTS) is having less impact than expected. This worrying situation is aggravated by coinfection with human immunodeficiency virus (HIV), and by the increase in drug-resistant strains. We need new insights that lead to more rapid therapies and immunotherapies, and more reliable vaccines. Recent insights have come from: understanding of the relationship between Mycobacterium tuberculosis and macrophages; the multiple T cell types that recognise mycobacterial peptides, lipids and glycolipids; the critical role of interferon-gamma (IFNgamma) and interleukin-12 (IL-12) in human mycobacterial infection revealed by genetically defective children; quantitation of the presence and importance of Th2 lymphocyte activation in human tuberculosis; the role of local conversion of inactive cortisone to active cortisol in the lesions; the recognition that some effective prophylactic vaccines also work as immumotherapeutics whereas others do not. In the longer term the recent sequencing of the M. tuberculosis genome will lead to further advances. In the short term, effective immunotherapy remains the most accessible breakthrough in the management of tuberculosis. The types of practical advance that will result from sequencing the genome are discussed speculatively, but cannot yet be predicted with certainty.

Polarization of PPD-specific T-cell response of patients with tuberculosis from Th0 to Th1 profile after successful antimycobacterial therapy or in vitro conditioning with interferon-alpha or interleukin-12

The T helper (Th) 1/Th2 balance in the T-lymphocyte response to purified protein derivative (PPD) was evaluated at the clonal level in six Italian and five Gambian patients with pulmonary tuberculosis (TB) before and after antimycobacterial therapy, as well as in five Gambian and four Italian healthy immune control subjects. In untreated patients, most PPD-specific clones derived from either peripheral blood or pleural effusions showed a Th0 cytokine profile (production of both interferon [IFN]-gamma and interleukin [IL]-4/IL-5). After 6 mo of therapy and clinical healing, most PPD-specific clones showed a polarized Th1 profile (production of IFN-gamma but not IL-4/IL-5) in both Italian and Gambian patients. The Th1 polarization was less marked in Gambian than in Italian patients and failed to occur in another group of four Italian patients who experienced treatment failure. The cytokine profile observed after successful therapy in patients with TB was similar to that found in healthy control subjects. T-cell clones of undefined specificity generated from PPD-stimulated cultures showed a similar Th0/Th2 bias in Gambian individuals and Italian patients with treatment failure. The Th0/Th2-biased responses in Gambian patients before therapy could be modulated in vitro by IFN-alpha or IL-12, which induced a Th1 polarization of both PPD-specific and bystander T cells. Our data show that active TB associates with a predominant Th0 response to mycobacterial antigens that could play a role in the pathogenesis of the disease. Adjunctive immunotherapy using Th1-polarizing cytokines could increase host defense against mycobacteria and accelerate healing.

Ineffective cellular immune response associated with T-cell apoptosis in susceptible Mycobacterium bovis BCG-infected mice

It has previously been reported that inhibition of delayed-type hypersensitivity-mediating functions of T cells during mycobacterial infection in mice is haplotype dependent. In the present study, we show that Mycobacterium bovis BCG infection induced, in susceptible C57BL/6 and BALB/c mice but not in resistant C3H/HeJ and DBA/2 mice, an important splenomegaly. An in vitro defect in T-cell proliferation in response to T-cell receptor (TCR) stimulation with mitogens or anti-CD3 antibodies was associated with enhanced levels of CD4(+) and CD8(+) T-cell apoptosis in susceptible but not in resistant mice 2 weeks after infection. Further investigations of C57BL/6 and C3H/HeJ mice revealed that in vivo splenomegaly was associated with destruction of the lymphoid tissue architecture, liver cellular infiltrates, and increased numbers of apoptotic cells in both spleen and liver tissue sections. Infection of C57BL/6 mice but not of C3H/HeJ mice induced massive production of tumor necrosis factor alpha (TNF-alpha) in serum, as well as an increase in Fas and Fas ligand (FasL) expression in T cells. In vitro addition of neutralizing anti-TNF-alpha antibodies led to a significant reduction in CD3-induced T-cell apoptosis of both CD4(+) and CD8(+) T cells of C57BL/6 mice, while the blockade of Fas-FasL interactions reduced apoptosis only in CD4(+) but not in CD8(+) T cells. Together, these results suggest that TNF-alpha and Fas-FasL interactions play a role in the activation-induced cell death (AICD) process associated with a defect in T-cell proliferation of the susceptible C57BL/6 mice. T-cell death by apoptosis may represent one of the important components of the ineffective immune response against mycobacterium-induced immunopathology in susceptible hosts.

Apoptosis in mycobacterium tuberculosis infection in mice exhibiting varied immunopathology

This study examined mechanisms contributing to pulmonary immunopathology following acute Mycobacterium tuberculosis (MTB) infection in vivo in a murine model. A/J and C57BL/6 mice were intravenously infected with MTB (Erdman). Pathological differences were found between strains, unrelated to pulmonary load of bacilli. A/J mice developed progressive interstitial pneumonitis, while C57BL/6 mice maintained granuloma formation. The contribution of FAS and FAS ligand-mediated apoptosis was assessed via bioluminescent reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemical staining, and TUNEL assessment of DNA fragmentation. Cytokine messages for pulmonary tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), as well as for the lytic molecules perforin and granzyme B, were quantified. Immunohistochemical staining for CD3 receptor was performed to monitor lymphocytic lung infiltration. Soon after infection, A/J mice exhibited increased pulmonary IFN-gamma message, concurrent with the appearance of CD3+ lymphocytes distributed throughout the lung. C57BL/6 mice exhibited perivascular cuffing, with no accompanying increase in IFN-gamma message. A/J mice also had elevated levels of FAS and FAS ligand message and protein early after infection, while the C57BL/6 mice had no increased expression of these molecules. Both strains exhibited qualitatively similar numbers of TUNEL-positive cells throughout infection, with a marked increase on day 7. Apoptotic cells appeared to co-localize with acid fast bacilli. It is therefore proposed that apoptosis during initial granuloma formation following MTB infection may occur through a FAS/FAS ligand-independent pathway. Moreover, a failure of completion of the FAS/FAS ligand-mediated apoptosis pathway in the A/J mice may contribute to inefficient elimination of lymphocytes, thus further aggravating pulmonary pathology.

Dichotomy of cytokine profiles in patients and high-risk healthy subjects exposed to tuberculosis

To better understand the role of cytokines in susceptible and resistant subjects exposed to Mycobacterium tuberculosis infection, intracellular gamma interferon (IFN-gamma) and interleukin-4 (IL-4) in ex vivo peripheral blood-derived CD4(+) T cells were examined by flow cytometry. Of the 37 individuals examined, 20 had clinical evidence of pulmonary tuberculosis and showed acid-fast bacilli in the sputum. Other individuals in close contact with these patients showed no evidence of disease. Patients had a higher number of CD4(+) T cells expressing IFN-gamma and IL-4 in unstimulated cultures compared to healthy subjects. Despite this, the ratio of IFN-gamma(+) to IL-4(+) CD4(+) T cells was similar in both groups. The Th1 response seen in CD4(+) T cells in patients was also observed in the overall pattern of IFN-gamma and IL-4 detected in control culture supernatants by enzyme-linked immunosorbent assay (ELISA). However, after in vitro stimulation of PBMC with heat-killed M. tuberculosis there was a significant reduction in the percentage of IFN-gamma(+) CD4(+) T cells (P < 0.001) in patients. This trend was reflected in the IFN-gamma ELISA assay with supernatants derived from stimulated cultures. However, the accumulated levels of IFN-gamma were higher than those for IL-4. The reduction of IFN-gamma(+) CD4(+) T cells resulted in the dominance of IL-4(+) CD4(+) T cells in 13 patients (P < 0.05). The elevated levels of IL-4(+) CD4(+) T cells seen in patients may contribute to the downregulation of IFN-gamma expression and the crucial effector function of CD4 T cells, leading to the persistence of disease and the immunopathology characteristically seen in patients. Preliminary data on the indicators of apoptosis in antigen-stimulated cultures in PBMC derived from patients are presented. Of the 17 high-risk healthy individuals examined, 11 differed in that, after mycobacterial-antigen stimulation, there was an enhancement in IFN-gamma(+) CD4(+) T cells.

Development of CD8alpha/alpha and CD8alpha/beta T cells in major histocompatibility complex class I-deficient mice

Peripheral CD8(+) T cells mainly use CD8alpha/beta, and their development is mainly dependent on the major histocompatibility complex (MHC) class I proteins K(b) and D(b) in H-2(b) mice. In this report, we have shown that the development of CD8alpha/beta TCR-alpha/beta cells in lymphoid organs as well as in intestinal intraepithelial lymphocytes (iIELs) is dependent on the MHC class I K(b) and D(b) proteins. In contrast, TCR-alpha/beta CD8alpha/alpha cells are found mainly in iIELs, and their numbers are unaffected in K(b)D(b) double knockout mice. Most of the TCR-gamma/delta cells in the iIELs also bear CD8alpha/alpha, and they are also unaffected in K(b)D(b) -/- mice. In beta2-microglobulin (beta2m)-deficient mice, all of the TCR-alpha/beta CD8alpha/alpha and CD8alpha/beta T cells disappear, but TCR-gamma/delta cells are unaffected by the absence of beta2m.