CTL-mediated killing of intracellular Mycobacterium tuberculosis is independent of target cell nuclear apoptosis

Mycobacterial Heat Shock Proteins in Sarcoidosis and Tuberculosis

Pathological similarities between sarcoidosis (SA) and tuberculosis (TB) suggest the role of mycobacterial antigens in the etiopathogenesis of SA. The Dubaniewicz group revealed that not whole mycobacteria, but Mtb-HSP70, Mtb-HSP 65, and Mtb-HSP16 were detected in the lymph nodes, sera, and precipitated immune complexes in patients with SA and TB. In SA, the Mtb-HSP16 concentration was higher than that of Mtb-HSP70 and that of Mtb-HSP65, whereas in TB, the Mtb-HSP16 level was increased vs. Mtb-HSP70. A high Mtb-HSP16 level, induced by low dose-dependent nitrate/nitrite (NOx), may develop a mycobacterial or propionibacterial genetic dormancy program in SA. In contrast to TB, increased peroxynitrite concentration in supernatants of peripheral blood mononuclear cell cultures treated with Mtb-HSP may explain the low level of NOx detected in SA. In contrast to TB, monocytes in SA were resistant to Mtb-HSP-induced apoptosis, and CD4+T cell apoptosis was increased. Mtb-HSP-induced apoptosis of CD8+T cells was reduced in all tested groups. In Mtb-HSP-stimulated T cells, lower CD8+γδ+IL-4+T cell frequency with increased TNF-α,IL-6,IL-10 and decreased INF-γ,IL-2,IL-4 production were present in SA, as opposed to an increased presence of CD4+γδ+TCR cells with increased TNF-α,IL-6 levels in TB, vs. controls. Mtb-HSP modulating the level of co-stimulatory molecules, regulatory cells, apoptosis, clonal deletion, epitope spread, polyclonal activation and molecular mimicry between human and microbial HSPs may also participate in the induction of autoimmunity, considered in SA. In conclusion, in different genetically predisposed hosts, the same antigens, e.g., Mtb-HSP, may induce the development of TB or SA, including an autoimmune response in sarcoidosis.

Vaccine-Induced Subcutaneous Granulomas in Goats Reflect Differences in Host-Mycobacterium Interactions between BCG- and Recombinant BCG-Derivative Vaccines

Tuberculous granulomas are highly dynamic structures reflecting the complex host-mycobacterium interactions. The objective of this study was to compare granuloma development at the site of vaccination with BCG and its recombinant derivatives in goats. To characterize the host response, epithelioid cells, multinucleated giant cells (MNGC), T cell subsets, B cells, plasma cells, dendritic cells and mycobacterial antigen were labelled by immunohistochemistry, and lipids and acid-fast bacteria (AFB) were labelled by specific staining. Granulomas with central caseous necrosis developed at the injection site of most goats though lesion size and extent of necrosis differed between vaccine strains. CD4+ T and B cells were more scarce and CD8+ cells were more numerous in granulomas induced by recombinant derivatives compared to their parental BCG strain. Further, the numbers of MNGCs and cells with lipid bodies were markedly lower in groups administered with recombinant BCG strains. Microscopic detection of AFB and mycobacterial antigen was rather frequent in the area of central necrosis, however, the isolation of bacteria in culture was rarely successful. In summary, BCG and its recombinant derivatives induced reproducibly subcutaneous caseous granulomas in goats that can be easily monitored and surgically removed for further studies. The granulomas reflected the genetic modifications of the recombinant BCG-derivatives and are therefore suitable models to compare reactions to different mycobacteria or TB vaccines.

A Mycobacterium avium subsp. paratuberculosis relA deletion mutant and a 35 kDa major membrane protein elicit development of cytotoxic T lymphocytes with ability to kill intracellular bacteria

Efforts to develop live attenuated vaccines against Mycobacterium avium subspecies paratuberculosis (Map), using indirect methods to screen Map deletion mutants for potential efficacy, have not been successful. A reduction in the capacity to survive in macrophages has not predicted the ability of mutants to survive in vivo. Previous studies for screening of three deletion mutants in cattle and goats revealed one mutant, with a deletion in relA (ΔMap/relA), could not establish a persistent infection. Further studies, using antigen presenting cells (APC), blood dendritic cells and monocyte derived DC, pulsed with ΔMap/relA or a 35 kDa Map membrane protein (MMP) revealed a component of the response to ΔMap/relA was directed towards MMP. As reported herein, we developed a bacterium viability assay and cell culture assays for analysis and evaluation of cytotoxic T cells generated against ΔMap/relA or MMP. Analysis of the effector activity of responding cells revealed the reason ΔMap/relA could not establish a persistent infection was that vaccination elicited development of cytotoxic CD8 T cells (CTL) with the capacity to kill intracellular bacteria. We demonstrated the same CTL response could be elicited with two rounds of antigenic stimulation of APC pulsed with ΔMap/relA or MMP ex vivo. Cytotoxicity was mediated through the perforin granzyme B pathway. Finally, cognate recognition of peptides presented in context of MHC I and II molecules to CD4 and CD8 T cells is required for development of CTL.

Cytotoxic cells kill intracellular bacteria through granulysin-mediated delivery of granzymes

When killer lymphocytes recognize infected cells, perforin delivers cytotoxic proteases (granzymes) into the target cell to trigger apoptosis. What happens to intracellular bacteria during this process is unclear. Human, but not rodent, cytotoxic granules also contain granulysin, an antimicrobial peptide. Here, we show that granulysin delivers granzymes into bacteria to kill diverse bacterial strains. In Escherichia coli, granzymes cleave electron transport chain complex I and oxidative stress defense proteins, generating reactive oxygen species (ROS) that rapidly kill bacteria. ROS scavengers and bacterial antioxidant protein overexpression inhibit bacterial death. Bacteria overexpressing a GzmB-uncleavable mutant of the complex I subunit nuoF or strains that lack complex I still die, but more slowly, suggesting that granzymes disrupt multiple vital bacterial pathways. Mice expressing transgenic granulysin are better able to clear Listeria monocytogenes. Thus killer cells play an unexpected role in bacterial defense.

Lymphocyte apoptosis in children with central nervous system tuberculosis: a case control study

Background

Studies of the apoptosis mechanisms involved in the pathogenesis of tuberculosis have suggested that Mycobacterium tuberculosis can actively interfere with the apoptosis of infected cells. In vivo studies have been performed in adult populations but have not focused on this process in children. In the present study, we analyzed spontaneous T lymphocyte (PBT) apoptosis in the peripheral blood of children with central nervous system tuberculosis (CNS TB), before and after chemotherapy, and compared the results with healthy controls.

Methods

A case-control study was conducted from January 2002 to June 2009. It included 18 children with CNS TB and 17 healthy controls. Spontaneous apoptosis of PBTs, including CD4⁺, CD8⁺ and CD8⁺/CD28⁺ T cells, was evaluated after 24 and 72 h of culture in complete medium, using the Annexin V detection test. Analysis was conducted before and after chemotherapy, and expression of the apoptotic markers CD95 (Fas) and Fas ligand (FasL) was evaluated.

Results

Higher percentages of apoptotic T cells and CD4 lymphocytes were isolated from children with acute phase CNS TB than from children in the control group (p < 0.05). This difference significantly decreased after 60 days of specific treatment. In children with CNS TB, high levels of Fas ligand expression were detected in lymphocyte populations, associated with a high percentage of Fas positive cells, before and after treatment. In contrast to the CD4+ apoptosis profile, we did not find any significant difference in total CD8⁺ cell apoptosis between children with acute phase disease and the control group. However, the percentage of apoptotic CD8⁺/CD28⁺ T cells was significantly higher in the children with acute phase disease than in the healthy controls.

Conclusions

Our findings indicate that CNS TB in pediatric patients increases the sensitivity of CD4 and CD8⁺/CD28⁺ T cells to apoptosis, suggesting a hypoergic status of this infection. This could play a key role in the immunopathogenesis of this complicated form of TB. Interestingly, specific chemotherapy is able to normalize both apoptosis sensitivity and T-cell activation.

MATHEMATICAL MODELING OF CHEMOTHERAPY OF HUMAN TB INFECTION

This work assesses the impact of the first line drug regimen on active disease control under the stipulated time of tuberculosis (TB) treatment. In an effort to understand why a robust immune response mechanism sometimes fails to completely control TB infection, we first developed a model that captures the human immune response mechanisms to Mycobacterium tuberculosis (Mtb) infection. We then extended the model to include drug therapy. The drug therapy model is used to assess the potency of the recommended six-month TB drug chemotherapy in infected individuals. The efficacy of each drug was explored and observations show that low drug efficacy values result in extension of treatment period. The numerical results confirm typical clinical disease progression patterns noticed in individuals under TB therapy. The drug model simulations and analysis show that administration of the recommended first line three-drug regimen normally cures the TB infection. Using the model, we established that only Isoniazid monotherapy drug treatment, and any combination therapy of two drugs including Isoniazid are potent enough to resolve the TB infection.

A lipopeptide facilitate induction of Mycobacterium leprae killing in host cells

Little is known of the direct microbicidal activity of T cells in leprosy, so a lipopeptide consisting of the N-terminal 13 amino acids lipopeptide (LipoK) of a 33-kD lipoprotein of Mycobacterium leprae, was synthesized. LipoK activated M. leprae infected human dendritic cells (DCs) to induce the production of IL-12. These activated DCs stimulated autologous CD4+ or CD8+ T cells towards type 1 immune response by inducing interferon-gamma secretion. T cell proliferation was also evident from the CFSE labeling of target CD4+ or CD8+ T cells. The direct microbicidal activity of T cells in the control of M. leprae multiplication is not well understood. The present study showed significant production of granulysin, granzyme B and perforin from these activated CD4+ and CD8+ T cells when stimulated with LipoK activated, M. leprae infected DCs. Assessment of the viability of M. leprae in DCs indicated LipoK mediated T cell-dependent killing of M. leprae. Remarkably, granulysin as well as granzyme B could directly kill M. leprae in vitro. Our results provide evidence that LipoK could facilitate M. leprae killing through the production of effector molecules granulysin and granzyme B in T cells.

Human yeast-specific CD8 T lymphocytes show a nonclassical effector molecule profile

Pathogenic yeast and fungi represent a major group of human pathogens. The consequences of infections are diverse and range from local, clinically uncomplicated mycosis of the skin to systemic, life-threatening sepsis. Despite extensive MHC class I-restricted frequencies of yeast-specific CD8 T lymphocytes in healthy individuals and the essential role of the cell-mediated immunity in controlling infections, the characteristics and defense mechanisms of antifungal effector cells are still unclear. Here, we describe the direct analysis of yeast-specific CD8 T lymphocytes in whole blood from healthy individuals. They show a unique, nonclassical phenotype expressing granulysin and granzyme K in lytic granules instead of the major effector molecules perforin and granzyme B. After stimulation in whole blood, yeast-specific CD8 T cells degranulated and, upon cultivation in the presence of IL-2, their granula were refilled with granulysin rather than with perforin and granzyme B. Moreover, yeast-specific stimulation through dendritic cells but not by yeast cells alone led to degranulation of the effector cells. As granulysin is the only effector molecule in lytic granules known to have antifungal properties, our data suggest yeast-specific CD8 T cells to be a nonclassical effector population whose antimicrobial effector machinery seems to be tailor-made for the efficient elimination of fungi as pathogens.

Exogenous control of the expression of Group I CD1 molecules competent for presentation of microbial nonpeptide antigens to human T lymphocytes

Group I CD1 (CD1a, CD1b, and CD1c) glycoproteins expressed on immature and mature dendritic cells present nonpeptide antigens (i.e., lipid or glycolipid molecules mainly of microbial origin) to T cells. Cytotoxic CD1-restricted T lymphocytes recognizing mycobacterial lipid antigens were found in tuberculosis patients. However, thanks to a complex interplay between mycobacteria and CD1 system, M. tuberculosis possesses a successful tactic based, at least in part, on CD1 downregulation to evade CD1-dependent immunity. On the ground of these findings, it is reasonable to hypothesize that modulation of CD1 protein expression by chemical, biological, or infectious agents could influence host's immune reactivity against M. tuberculosis-associated lipids, possibly affecting antitubercular resistance. This scenario prompted us to perform a detailed analysis of the literature concerning the effect of external agents on Group I CD1 expression in order to obtain valuable information on the possible strategies to be adopted for driving properly CD1-dependent immune functions in human pathology and in particular, in human tuberculosis.

Cytotoxicity responses to selected ESAT-6 and CFP-10 peptides in tuberculosis

Cytotoxicity responses were studied for the ESAT-6 peptides Esp1, Esp6, Esp7, Esp8, and CFP-10 peptides, Cfp6, Cfp7, Cfp8, Cfp9 (synthetic 20-mer peptides) and the recombinant ESAT-6, CFP-10 proteins. Cytolytic molecules perforin, granzymes A and B, granulysin responses in healthy household contacts (HHC) and pulmonary tuberculosis patients (PTB), were studied by intracellular flow cytometry. Functional cytotoxicity was studied in both the groups for the peptides Esp6 and Cfp8 by an enzyme (lactate dehydrogenase) based assay. The results revealed that cytolytic molecule positive CD4+ and CD8+ T cells were increased in HHC in response to Esp1, Esp6, Cfp8 and Cfp9 immunogenic peptides compared to PTB. Functional cytotoxicity results showed higher cytotoxicity (not statistically significant) to be exhibited by the peptide Esp6 than Cfp8 in the HHC.

Perforin: more than just a pore-forming protein

Cellular apoptosis induced by T cells is mainly mediated by two pathways. One, granule exocytosis utilizes perforin/granzymes. The other involves signaling through death receptors of the TNF-alpha R super-family, especially FasL. Perforin plays a central role in apoptosis induced by granzymes. However, the mechanisms of perforin-mediated cytotoxicity are still not elucidated completely. Perforin is not only a pore-forming protein, but also performs multiple biological functions or perforin performs one biological function (cytolysis), but has multiple biological implications in the cellular immune responses, including regulation of proliferation of CD8+ CTLs.

TNF-alpha is a positive regulatory factor for human Vgamma2 Vdelta2 T cells

Vgamma2 Vdelta2 T cells in human peripheral blood recognize phosphoantigen and play important roles in host defense and immunoregulation. The TCR is required for Vgamma2 Vdelta2 T cell responses to phosphoantigen, but less is known about soluble or cell-associated costimulatory molecules. In this study, we show that human Vgamma2 Vdelta2 T cell responses to phosphoantigen, including activation, proliferation, cytokine production, and tumor cell cytotoxicity, require TNF-alpha binding to its receptor, with a preference for TNFR2. Because stimulated Vgamma2 Vdelta2 cells also produce TNF-alpha, this may be a positive control mechanism to sustain the response. Impaired proliferation in the presence of TNF-alpha or TNFR blocking agents was partially rescued by a TLR2 agonist, Pam(3)Cys. Our studies demonstrate that TNF-alpha plays a critical role in regulating human Vgamma2 Vdelta2 T cell immune responses.

Mycobacteria and innate cells: critical encounter for immunogenicity

Protective immunity against mycobacterial infections such as Mycobacterium tuberculosis is mediated by interactions between specific T cells and activated macrophages. To date,many aspects of mycobacterial immunity have shown that innate cells are the key elements that substantially influence the subsequent adaptive host response. During the early phases of infection,phagocytic cells and innate lymphocyte subsets play a pivotal role. Here we summarize the findings of recent investigations on macrophages,dendritic cells and gammadelta T lymphocytes in the response to mycobacteria.

Mycobacterium bovis BCG vaccination induces memory CD4+ T cells characterized by effector biomarker expression and anti-mycobacterial activity

The effector mechanisms used by CD4+ T cells to control mycobacteria differ between humans and rodent models of TB and should be investigated in additional animal models. In these studies, the bovine model was used to characterize the mycobactericidal CD4+ T cell response induced by vaccination with the attenuated Mycobacterium bovis bacillus Calmette-Guérin (BCG). Antigenic stimulation of peripheral blood CD4+ T cells from BCG-vaccinated cattle enhanced expression of perforin and IFNgamma in cells expressing a CD45RA-CD45RO+CD62L+ cell surface phenotype, enhanced transcription of granulysin, IFNgamma, perforin, IL-4, IL-13, and IL-21, and enhanced anti-mycobacterial activity of CD4+ T cells against BCG-infected macrophages.

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

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

Functional characterization of a T-cell receptor BV6+ T-cell clone derived from a leprosy lesion

Human infection with Mycobacterium leprae, an intracellular bacterium, presents as a clinical and immunological spectrum; thus leprosy provides an opportunity to investigate mechanisms of T-cell responsiveness to a microbial pathogen. Analysis of the T-cell receptor (TCR) repertoire in leprosy lesions revealed that TCR BV6(+) T cells containing a conserved CDR3 motif are over-represented in lesions from patients with the localized form of the disease. Here, we derived a T-cell clone from a leprosy lesion that expressed TCR BV6 and the conserved CDR3 sequence L-S-G. This T-cell clone produced a T helper type 1 cytokine pattern, directly lysed M. leprae-pulsed antigen-presenting cells by the granule exocytosis pathway, and expressed the antimicrobial protein granulysin. BV6(+) T cells may therefore functionally contribute to the cell-mediated immune response against M. leprae.

Cytotoxic CD4+ T cells use granulysin to kill Cryptococcus neoformans, and activation of this pathway is defective in HIV patients

An important mechanism of host defense to Cryptococcus neoformans involves the direct microbicidal activity of lymphocytes. The importance of CD4+ T cells is illustrated by the incidence of this infection in the acquired immunodeficiency syndrome (AIDS) patients; however, the relative activity of microbicidal CD4+ T cells compared with CD8+ T cells and natural killer (NK) cells has not been established. Further, although NK cells and CD8+ T cells use perforin or granulysin, respectively, to kill C neoformans, the effector molecule used by CD4+ T cells is not known. Experiments demonstrated that IL-2-activated peripheral blood lymphocytes from healthy adults acquire anticryptococcal activity, and surprisingly, that CD4+ T cells had the most profound effect on this activity. Using SrCl(2)induced degranulation and siRNA knockdown, granulysin was shown to be the effector molecule. Although activation by anti-CD3 + IL-2 resulted in the additional expression of perforin, this did not improve the anticryptococcal activity. Cryptococcal killing by CD4+ T cells was defective in human immunodeficiency virus (HIV)-infected patients due to dysregulated granulysin and perforin production in response to IL-2 or anti-CD3 + IL-2. In conclusion, CD4+ T cells are the major subset of cells responsible for killing C neoformans in peripheral blood. These cells use granulysin as the effector molecule, and priming is dysregulated in HIV-infected patients, which results in defective microbicidal activity.

Recombinant M. smegmatis vaccine targeted delivering IL-12/GLS into macrophages can induce specific cellular immunity against M. tuberculosis in BALB/c mice

In the present study, we constructed a viable therapeutic vaccine of recombinant M. smegmatis mediated IL-12/GLS (granulysin) gene transfer into murine macrophages to exert the immunotherapy effects on the Mycobacterium tuberculosis infection. We tested this recombinant therapeutic vaccine in an in vivo study to determine its capability of stimulating host specific immune responses against M. tuberculosis. BALB/c mice intranasally immunized with the therapeutic vaccine developed an efficient Th1 protective immune response against M. tuberculosis which was equal to that of the BCG strain. Inoculation intranasally with this viable vaccine induced high level of serum IFN-gamma, IL-12 and IgG2a. The viable vaccine was capable of inducing purified protein derivative (PPD) antigen-specific splenocytes proliferation and IFN-gamma production from T cells in spleens of the immunized mice. In addition, intranasally inoculation with the viable vaccine can induce PPD antigen-specific sIgA production in the broncho-alveolar lavage fluid (BALF) of the immunized mice. No change of IL-4 level was found in all groups. The therapeutic mechanism of this viable vaccine against M. tuberculosis infection observed here appeared to be a result of the specific Th1 immune response activated by mycobacterium antigen from M. smegmatis and the expression of sIL-12/GLS in alveolar macrophages via the M. smegmatis-mediated gene transfer method. This research demonstrates that the therapeutic gene can be introduced into a host by viable mycobacteria works to induce the host specific immune response against M. tuberculosis infection in vivo. Since this therapeutic vaccine can strongly induce specific Th1 responses against M. tuberculosis in BALB/c mice and has no obviously harmfulness to the host simultaneously, the recombinant vaccine might be a potential candidate therapeutic vaccine against tuberculosis.

An intradermal environment promotes a protective type-1 response against lethal systemic monocytotropic ehrlichial infection

Immune responses against monocytotropic ehrlichiosis during infection with a strain of Ehrlichia from Ixodes ovatus (IOE) were evaluated using a model that closely reproduces the pathology and immunity associated with tick-transmitted human monocytotropic ehrlichiosis. C57BL/6 mice were inoculated intradermally or intraperitoneally with high-dose highly virulent IOE or intraperitoneally with mildly virulent Ehrlichia muris. Intradermal (i.d.) infection with IOE established mild, self-limited disease associated with minimal hepatic apoptosis, and all mice survived past 30 days. Intraperitoneal (i.p.) infection with IOE resulted in acute, severe toxic shock-like syndrome and severe multifocal hepatic apoptosis and necrosis, and all mice succumbed to disease. Compared to i.p. infection with IOE, intradermally infected mice had a 100- to 1,000-fold lower bacterial load in the spleen with limited dissemination. Compared to mice infected intraperitoneally with IOE, i.d. infection stimulated a stronger protective type-1 cell-mediated response on day 7 of infection, characterized by increased percentages of both CD4+ and CD8+ splenic T cells, generation of a greater number of IOE-specific, gamma interferon-producing CD4+ Th1 cells, and higher levels of tumor necrosis factor (TNF-alpha) in the spleen but lower concentrations of serum TNF-alpha and interleukin-10. These data suggest that under the conditions of natural route of challenge (i.e., i.d. inoculation), the immune response has the capacity to confer complete protection against monocytotropic ehrlichiosis, which is associated with a strong cell-mediated type-1 response and decreased systemic production of pro- and anti-inflammatory cytokines.

Pneumocystis Cell Wall β-Glucans Induce Dendritic Cell Costimulatory Molecule Expression and Inflammatory Activation through a Fas-Fas Ligand Mechanism

Respiratory failure during Pneumocystis pneumonia is mainly a consequence of exaggerated inflammatory responses to the organism. Dendritic cells (DCs) are the most potent APCs in the lung and are key to the regulation of innate and adaptive immune responses. However, their participation in the inflammatory response directed against Pneumocystis infection has not been fully elucidated. Therefore, we studied the role of Pneumocystis carinii, as well as Saccharomyces cerevisiae, cell wall-derived beta-glucans, in DC costimulatory molecule expression. We further studied the impact of beta-glucans on subsequent T cell activation. Because cytokine secretion by DCs has recently been shown to be regulated by Fas ligand (FasL), its role in beta-glucan activation of DCs was also investigated. beta-Glucan-induced DC activation occurred in part through dectin-1 receptors. We demonstrated that DC activation by beta-glucans elicits T cell activation and polarization into a Th1 patterned response, but with the conspicuous absence of IL-12. These observations differed from LPS-driven T cell polarization, suggesting that beta-glucans and LPS signal DC activation through different mechanisms. We additionally determined that IL-1beta and TNF-alpha secretion by beta-glucan-stimulated DCs was partially regulated by Fas-FasL. This suggests that dysregulation of FasL could further enhance exuberant and prolonged cytokine production by DCs following DC-T cell interactions, further promoting lung inflammation typical of Pneumocystis pneumonia.

Comparative Analysis of Mycobacterial Heat Shock Proteins-Induced Apoptosis of Peripheral Blood Mononuclear Cells in Sarcoidosis and Tuberculosis

Sarcoidosis (SA) is a granulomatous disorder of an unknown etiology. Mycobacterium tuberculosis heat shock proteins (Mtb-hsp), considered as causative agents, play an important role in apoptosis. A role for apoptosis has been proposed in pathogenesis of SA and tuberculosis (TB) granuloma formation but results remain controversial. Differences in Mtb-hsp-induced apoptosis between SA, TB, and healthy subjects found in this study might put some light on the etiology of SA. Early apoptotic peripheral blood mononuclear cells (PBMC) were determined in 22 SA patients, 20 TB patients, and 20 healthy volunteers by flow cytometry (Annexin-V-FITC). Our results revealed that spontaneous apoptosis of monocytes and CD8+ T-cells was comparable between tested groups. Apoptosis of unstimulated CD4+ T-cells was significantly lower in TB versus controls and insignificantly lower versus SA. Mtb-hsp- and PHA (Phytohemagglutinin)-induced monocytes apoptosis was significantly lower in TB versus controls and SA. Mtb-hsp-induced CD4+ T-cell apoptosis was significantly lower in TB versus controls and SA. There were no differences of PHA-induced CD4+ T-cell and CD8+ T-cell apoptosis between tested groups. Apoptosis of Mtb-hsp-induced CD8+ T-cells was significantly lower in TB and SA versus controls. Analysis of PBMC apoptosis before and after stimulation in each tested group revealed that, in contrast to TB, sarcoid monocytes were resistant to Mtb-hsp- and PHA-induced apoptosis and CD4+ T-cells were resistant to PHA- but not Mtb-hsp-induced apoptosis. CD8+ T-cell apoptosis, before and after Mtb-hsp or PHA stimulation, was significantly increased in all tested groups. It seems likely that dysregulated apoptosis of CD4+ T-cells and resistant apoptosis monocytes may be involved in pathogenesis of SA.

Mycobacterium tuberculosis growth control by lung macrophages and CD8 cells from patient contacts

RATIONALE

Healthy household contacts (HHCs) of patients with active pulmonary tuberculosis are exposed aerogenically to Mycobacterium tuberculosis (Mtb), thus permitting the study of protective local immunity.

OBJECTIVES

To assess alveolar macrophage (AM) and autologous blood CD4 and CD8 T-cell-mediated Mtb growth control in HHCs and healthy, unexposed community control subjects (CCs).

METHODS

AMs were infected with Mtb strains H(37)Ra and H(37)Rv at multiplicities of infection 0.1 and 1. Mtb colony-forming units were evaluated on Days 1, 4, and 7.

MAIN RESULTS

CD8 T cells from HHCs in 1:1 cocultures with AMs significantly (p < 0.05) increased Mtb growth control by AMs. In CCs, no detectable contribution of CD8 T cells to Mtb growth control was observed. CD4 T cells did not increase Mtb growth control in HHCs or in CCs. IFN-gamma, nitric oxide, and tumor necrosis factor were determined as potential mediators of Mtb growth control in AMs and AM/CD8 and AM/CD4 cocultures. IFN-gamma production in AM/CD4 was twofold higher than that in AM/CD8 cocultures in both HHCs and CCs (p < 0.05). Nitric oxide production from AMs of HHCs increased on Days 4 and 7 and was undetectable in AMs from CCs. IFN-gamma and nitric acid concentrations and Mtb growth control were not correlated. Tumor necrosis factor levels were significantly increased in AM/CD8 cocultures from HHCs compared with AM/CD8 cocultures from CCs (p < 0.05).

CONCLUSION

Aerogenic exposure to Mtb in HHCs leads to expansion of Mtb-specific effector CD8 T cells that limit Mtb growth in autologous AMs.

[Granulysin: antimicrobial molecule of innate and acquired immunity in human tuberculosis]

The recent global increase in cases of tuberculosis and the emergence of multidrug-resistant strains of tuberculosis have focused attention on the molecular mechanisms of human antimycobacterial immunity. The macrophage is not only the primary site for Mycobacterium tuberculosis growth but also ordinarily provides the primary lines of host defense against invading pathogens in its role as an effector of innate immunity. The ability of M. tuberculosis to survive and replicate in the host macrophage is critical to its pathogenesis, emphasizing a need for a clearer understanding of its interactions with the host macrophage. Macrophages use varied strategies to kill and destroy invading organisms, including production of reactive nitrogen and oxygen intermediates, phagosome maturation and acidification, fusion with lysosomes, exposure to defensins and host cell apoptosis. In human, granulysin is a recently identified antimicrobial protein expressed on cytotoxic T cells, natural killer (NK) cells and NKT cells. It has been shown that granulysin contributes to the defense mechanisms against mycobacterial infection. We hypothesized that human macrophages may possess antimicrobial substances, such as granulysin, and play a role in the defense mechanism.

Gamma delta T cell responses associated with the development of tuberculosis in health care workers

This study evaluated T cell immune responses to purified protein derivative (PPD) and Mycobacterium tuberculosis (Mtb) in health care workers who remained free of active tuberculosis (HCWs w/o TB), health care workers who went on to develop active TB (HCWs w/TB), non-health care workers who were TB free (Non-HCWs) and tuberculosis patients presenting with minimal (Min TB) or advanced (Adv TB) disease. Peripheral blood mononuclear cells (PBMC) were stimulated with Mtb and PPD and the expression of T cell activation markers CD25+ and HLA-DR+, intracellular IL-4 and IFN-gamma production and cytotoxic responses were evaluated. PBMC from HCWs who developed TB showed decreased percentages of cells expressing CD8+CD25+ in comparison to HCWs who remained healthy. HCWs who developed TB showed increased gammadelta TCR+ cell cytotoxicity and decreased CD3+gammadelta TCR- cell cytotoxicity in comparison to HCWs who remained healthy. PBMC from TB patients with advanced disease showed decreased percentages of CD25+CD4+ and CD25+CD8+ T cells that were associated with increased IL-4 production in CD8+ and gammadelta TCR+ phenotypes, in comparison with TB patients presenting minimal disease. TB patients with advanced disease showed increased gammadelta TCR+ cytotoxicity and reduced CD3+gammadelta TCR- cell cytotoxicity. Our results suggest that HCWs who developed TB show an early compensatory mechanism involving an increase in lytic responses of gammadelta TCR+ cells which did not prevent TB.

Specific lytic activity against mycobacterial antigens is inversely correlated with the severity of tuberculosis

The ability of peripheral blood mononuclear cells (PBMC) from patients with active tuberculosis to display cytotoxic responses against autologous Mycobacterium tuberculosis (Mtb)-pulsed macrophages was evaluated. Non-MHC restricted cell-dependent lytic activity was observed in ex vivo effector cells from tuberculosis patients and was mediated mainly by CD3(+)gammadelta TCR(+) T (gammadelta T) cells bearing CD56 and/or CD16 molecules. MHC-restricted and non-MHC restricted cytotoxic T cells (CTL) were differentially expanded upon stimulation with Mtb in tuberculosis patients and normal controls (N). Class-I restricted CD8(+) CTL and class-II restricted CD4(+) CTL were generated in PPD(+)N and to a lesser extent in PPD(-)N. Mtb-stimulated effector cells from tuberculosis patients became progressively non-MHC restricted CD4(-)CD8(-)gammadelta T cells, while lytic activity of CD4(+) and CD8(+)CTL decreased gradually as the disease became more severe. On the other hand, target cells were lysed by ex vivo cells from tuberculosis patients through the Fas-FasL and perforin pathways. Mtb-induced CD4(+) CTL from tuberculosis patients and N controls preferentially employed the Fas-FasL mechanism. Mtb-induced CD8(+) CTL effector cells from patients used the perforin-based mechanism while cells from N controls also used the Fas-FasL pathway. While Mtb-induced gammadelta CTL from patients and PPD(-)N employed the latter mechanism cells from PPD(+)N individuals also used the perforin pathway. It can be concluded that shifts in the CTL response and the cytolytic mechanisms take place as the pulmonary involvement becomes more severe.

Human NKT cells express granulysin and exhibit antimycobacterial activity

Human NKT cells are a unique subset of T cells that express an invariant V alpha 24 TCR that recognizes the nonclassical Ag-presenting molecule CD1d. Activation of NKT cells is greatly augmented by the marine sponge-derived glycolipid alpha-galactosylceramide (alpha GalCer). Because human monocyte-derived cells express CD1d and can harbor the intracellular pathogen Mycobacterium tuberculosis, we asked whether the addition of alpha GalCer could be used to induce effector functions of NKT cells against infected monocytes, macrophages, and monocyte-derived dendritic cells. NKT cells secreted IFN-gamma, proliferated, and exerted lytic activity in response to alpha GalCer-pulsed monocyte-derived cells. Importantly, alpha GalCer-activated NKT cells restricted the growth of intracellular M. tuberculosis in a CD1d-dependent manner. NKT cells that exhibited antimycobacterial activity also expressed granulysin, an antimicrobial peptide shown to mediate an antimycobacterial activity through perturbation of the mycobacterial surface. Degranulation of NKT cells resulted in depletion of granulysin and abrogation of antimycobacterial activity. The detection of CD1d in granulomas of tuberculosis patients supports the potential interaction of NKT cells with CD1d-expressing cells at the site of disease activity. These studies provide evidence that alpha Gal Cer-activated CD1d-restricted T cells can participate in human host defense against M. tuberculosis infection.

Assessment of cell mediated immunogenicity of Mycobacterium leprae-derived antigens

The antigenicity of Mycobacterium leprae (M. leprae)-derived cell membrane fraction was examined using human dendritic cells (DCs). Immature DCs internalized and processed the cell membrane components, and expressed M. leprae-derived antigens (Ags) on their surface. The expression of MHC class II, CD86, and CD83 Ags on DCs and CD40 ligand (L)-associated IL-12 p70 production from DCs were up-regulated by the membrane Ags. Moreover these stimulated DCs induced significantly higher level of interferon-gamma (IFN-gamma) production by autologous CD4(+) and CD8(+) T cells than those pulsed with equivalent doses of live M. leprae or its cytosol fraction. Both subsets of T cells from tuberculoid leprosy patients also produced several fold more IFN-gamma than those from normal individuals. Furthermore, the intracellular perforin production in CD8(+) T cells was up-regulated in an Ag-dose dependent manner. These results suggest that M. leprae membrane Ags might be useful as the vaccinating agents against leprosy.

Granulysin crystal structure and a structure-derived lytic mechanism

Our crystal structure of granulysin suggests a mechanism for lysis of bacterial membranes by granulysin, a 74-residue basic protein from human cytolytic T lymphocyte and natural killer cells. We determined the initial crystal structure of selenomethionyl granulysin by MAD phasing at 2A resolution. We present the structure model refined using native diffraction data to 0.96A resolution. The five-helical bundle of granulysin resembles other "saposin folds" (such as NK-lysin). Positive charges distribute in a ring around the granulysin molecule, and one face has net positive charge. Sulfate ions bind near the segment of the molecule identified as most membrane-lytic and of highest hydrophobic moment. The ion locations may indicate granulysin's orientation of initial approach towards the membrane. The crystal packing reveals one way to pack a sheet of granulysin molecules at the cell surface for a concerted lysis effort. The energy of binding granulysin charges to the bacterial membrane could drive the subsequent lytic processes. The loosely packed core facilitates a hinge or scissors motion towards exposure of hydrophobic surface that we propose tunnels the granulysin into the fracturing target membrane.

CD8 T cell-mediated killing of Cryptococcus neoformans requires granulysin and is dependent on CD4 T cells and IL-15

Granulysin is located in the acidic granules of cytotoxic T cells. Although the purified protein has antimicrobial activity against a broad spectrum of microbial pathogens, direct evidence for granulysin-mediated cytotoxicity has heretofore been lacking. Studies were performed to examine the regulation and activity of granulysin expressed by CD8 T cells using Cryptococcus neoformans, which is one of the most common opportunistic pathogens of AIDS patients. IL-15-activated CD8 T cells acquired anticryptococcal activity, which correlated with the up-regulation of granulysin. When granules containing granulysin were depleted using SrCl(2,) or when the gene was silenced using 21-nt small interfering RNA duplexes, the antifungal effect of CD8 T cells was abrogated. Concanamycin A and EGTA did not affect the antifungal effect, suggesting that the activity of granulysin was perforin independent. Following stimulation by the C. neoformans mitogen, CD8 T cells expressed granulysin and acquired antifungal activity. This activity required CD4 T cells and was dependent upon accessory cells. Furthermore, IL-15 was both necessary and sufficient for granulysin up-regulation in CD8 T cells. These observations are most consistent with a mechanism whereby C. neoformans mitogen is presented to CD4 T cells, which in turn activate accessory cells. The resultant IL-15 activates CD8 T cells to express granulysin, which is responsible for antifungal activity.

Mycobacterium leprae infection in monocyte-derived dendritic cells and its influence on antigen-presenting function

Host defense against Mycobacterium leprae infection is chiefly mediated by gamma interferon (IFN-gamma)-secreting cytotoxic T cells. Since which antigen-presenting cell populations act to stimulate these T cells is not fully understood, we addressed the role of monocyte-derived dendritic cells (DCs). The DCs phagocytosed M. leprae and expressed bacterially derived antigens (Ags), such as phenolic glycolipid 1 (PGL-1), in the cytoplasm, as well as on the cell surface. The expression of HLA-ABC and -DR Ags on DCs was down-regulated by M. leprae infection, and that of CD86 was up-regulated, but not as fully as by Mycobacterium bovis BCG infection. Induction of CD83 expression required a large number of M. leprae cells. When a multiplicity of infection of >40 was used, the DCs induced a significant proliferative and IFN-gamma-producing response in autologous T cells. However, these responses were significantly lower than those induced by BCG- or Mycobacterium avium-infected DCs. A CD40-mediated signaling in M. leprae-infected DCs up-regulated the expression of HLA Ags, CD86, and CD83 but did not enhance T-cell-stimulating ability. Therefore, M. leprae-infected DCs are less efficient at inducing T-cell responses. However, when the surface PGL-1 on M. leprae-infected DCs was masked by a monoclonal antibody, the DCs induced enhanced responses in both CD4(+)- and CD8(+)-T-cell subsets. M. leprae is a unique pathogen which remains resistant to DC-mediated T-cell immunity, at least in the early stages of infection.

Cytotoxic T lymphocytes: all roads lead to death

Cytotoxic T lymphocytes (CTLs) provide potent defences against virus infection and intracellular pathogens. However, CTLs have a dark side--their lytic machinery can be directed against self-tissues in autoimmune disorders, transplanted cells during graft rejection and host tissues to cause graft-versus-host disease, which is one of the most serious diseases related to CTL function. Although this duplicitous behaviour might seem contradictory, both beneficial and detrimental effects are the result of the same effector proteins. So, an understanding of the mechanisms that are used by CTLs to destroy targets and a knowledge of pathogen immune-evasion strategies will provide vital information for the design of new therapies.

Cytokine production and cytolytic mechanism of CD4(+) cytotoxic T lymphocytes in ex vivo expanded therapeutic Epstein-Barr virus-specific T-cell cultures

Ex vivo expanded Epstein-Barr virus (EBV)-specific T cells have been successfully applied clinically for adoptive immunotherapy. However, the role of CD4(+) T cells in the therapeutic T-cell culture has not been established for the reconstitution of EBV-specific immunity. We isolated and characterized CD4(+) T-cell lines from the ex vivo T-cell cultures. Monoclonal line PD-F4 and oligoclonal lines ND-R4 and TD-B4 were CD3(+)CD4(+)CD8(-). Cytolytic tests with targets of mismatched major histocompatibility complex (MHC) and anti-MHC antibodies confirmed that the cytotoxicity of these CD4(+) cells was restricted by MHC class II. Single cells of ND-R4 expressed interferon-gamma (IFN-gamma, or interleukin 4 (IL-4), but rarely coexpressed these 2 cytokines. In contrast, PD-F4 coexpressed IFN-gamma, IL-2, and IL-4. Kinetic studies with PD-F4 showed that expression of the 3 cytokines plateaued 5 hours upon stimulation and was then drastically reduced, with a pattern consistent with independent modulation and differential off-cycle signal requirements. The cytotoxicity of these CD4(+) cells was largely resistant to brefeldin A, an inhibitor for cytolytic pathways by Fas-ligand family molecules. Although sensitive to concanamycin A and ethyleneglycotetraacetic acid, which inhibit cytotoxicity by granule exocytosis, the CD4(+) cytotoxic T lymphocytes (CTLs) did not express perforin, suggesting a cytotoxic mechanism independent of perforin although involving exocytosis. Flow cytometric analysis showed that the CD4(+) CTLs expressed granulysin, a recently identified cytolytic molecule associated with exocytotic cytolytic granules. These data suggested that CD4(+) T cells in the therapeutic B-lymphoblastoid cell lines-primed T-cell culture are diverse in producing T(H)1 and T(H)2 cytokines, and may exert specific cytotoxicity via exocytosis of granulysin.

Adult tuberculosis in the 21st century: pathogenesis, clinical features, and management

This article reviews the significant advances in the past year in the basic and clinical aspects of adult tuberculosis (TB). Further research has deepened our understanding of host susceptibility and resistance mechanisms, including cytotoxicity, apoptosis, and antimicrobial polypeptides such as granulysin. Studies have confirmed the effects of HIV infection on risk of disease and disease manifestations, and have defined the effects of HIV on TB transmission. Recent studies also indicate a possible role for extended treatment of active disease and latent infection in HIV-1 infected individuals. Multidrug-resistant disease has been reported on every continent; rapid molecular approaches to the simultaneous diagnosis of TB and detection of rifampin resistance may facilitate prompt initiation of treatment. TB remains one of the major problems in global health.