Immune regulation of gammadelta T cell responses in mycobacterial infections

Characterization and anti-tuberculosis effects of γδ T cells expanded and activated by Mycobacterium tuberculosis heat-resistant antigen

Tuberculosis (TB) is a chronic infectious disease caused by Mycobacterium tuberculosis (Mtb) that poses a severe threat to human health. A variety of highly immunogenic tuberculosis proteins have been used as targets in vaccine development to mitigate the spread of TB. Although Th1-type immunity has long been considered a crucial part of resistance to Mtb, γδ T cells, the predominant source of IL-17, are not negligible in controlling the early stages of TB infection. In addition to classical phosphoantigens, Mycobacterium tuberculosis heat-resistant antigens (HAg), a complex containing 564 proteins obtained from live tuberculosis bacteria after heat treatment at 121 °C for 20 min, have been confirmed to be highly effective γδ T cell stimulators as well. Several studies have demonstrated that HAg-activated γδ T cells can participate in TB immunity by secreting multiple cytokines against Mtb or by interacting with other innate immune cells. In this review, we present a possible mechanism of HAg stimulation of γδ T cells and the role of HAg-activated γδ T cells in anti-TB immunity. We also highlight the limitations of studies on HAg activation of γδ T cells and suggest further research directions on the relationship between HAg and γδ T cells.

γδ T Cells Support Antigen-Specific αβ T cell-Mediated Antitumor Responses during BCG Treatment for Bladder Cancer

Bacillus Calmette-Guérin (BCG) is the most effective intravesical agent at reducing recurrence for patients with high-grade, non-muscle-invasive bladder cancer. Nevertheless, response to BCG is variable and strategies to boost BCG efficacy have not materialized. Prior work demonstrated a requirement for either conventional αβ or nonconventional γδ T cells in mediating BCG treatment efficacy, yet the importance of T-cell antigen specificity for BCG's treatment effect is unclear. Here, we provide direct evidence to show that BCG increases the number of tumor antigen-specific αβ T cells in patients with bladder cancer and protects mice from subsequent same-tumor challenge, supporting BCG induction of tumor-specific memory and protection. Adoptive T-cell transfers of antigen-specific αβ T cells into immunodeficient mice challenged with syngeneic MB49 bladder tumors showed that both tumor and BCG antigen-specific αβ T cells contributed to BCG efficacy. BCG-specific antitumor immunity, however, also required nonconventional γδ T cells. Prior work shows that the mTOR inhibitor rapamycin induces the proliferation and effector function of γδ T cells. Here, rapamycin increased BCG efficacy against both mouse and human bladder cancer in vivo in a γδ T cell-dependent manner. Thus, γδ T cells augment antitumor adaptive immune effects of BCG and support rapamycin as a promising approach to boost BCG efficacy in the treatment of non-muscle-invasive bladder cancer.

Human T-bet Governs Innate and Innate-like Adaptive IFN-γ Immunity against Mycobacteria

Inborn errors of human interferon gamma (IFN-γ) immunity underlie mycobacterial disease. We report a patient with mycobacterial disease due to inherited deficiency of the transcription factor T-bet. The patient has extremely low counts of circulating Mycobacterium-reactive natural killer (NK), invariant NKT (iNKT), mucosal-associated invariant T (MAIT), and Vδ2+ γδ T lymphocytes, and of Mycobacterium-non reactive classic TH1 lymphocytes, with the residual populations of these cells also producing abnormally small amounts of IFN-γ. Other lymphocyte subsets develop normally but produce low levels of IFN-γ, with the exception of CD8+ αβ T and non-classic CD4+ αβ TH1∗ lymphocytes, which produce IFN-γ normally in response to mycobacterial antigens. Human T-bet deficiency thus underlies mycobacterial disease by preventing the development of innate (NK) and innate-like adaptive lymphocytes (iNKT, MAIT, and Vδ2+ γδ T cells) and IFN-γ production by them, with mycobacterium-specific, IFN-γ-producing, purely adaptive CD8+ αβ T, and CD4+ αβ TH1∗ cells unable to compensate for this deficit.

Adults from Kisumu, Kenya have robust γδ T cell responses to Schistosoma mansoni, which are modulated by tuberculosis

Schistosoma mansoni (SM) is a parasitic helminth that infects over 200 million people and causes severe morbidity. It undergoes a multi-stage life cycle in human hosts and as such stimulates a stage-specific immune response. The human T cell response to SM is complex and varies throughout the life cycle of SM. Relative to the wealth of information regarding the immune response to SM eggs, little is known about the immune response to the adult worm. In addition, while a great deal of research has uncovered mechanisms by which co-infection with helminths modulates immunity to other pathogens, there is a paucity of data on the effect of pathogens on immunity to helminths. As such, we sought to characterize the breadth of the T cell response to SM and determine whether co-infection with Mycobacterium tuberculosis (Mtb) modifies SM-specific T cell responses in a cohort of HIV-uninfected adults in Kisumu, Kenya. SM-infected individuals were categorized into three groups by Mtb infection status: active TB (TB), Interferon-γ Release Assay positive (IGRA+), and Interferon-γ Release Assay negative (IGRA-). U.S. adults that were seronegative for SM antibodies served as naïve controls. We utilized flow cytometry to characterize the T cell repertoire to SM egg and worm antigens. We found that T cells had significantly higher proliferation and cytokine production in response to worm antigen than to egg antigen. The T cell response to SM was dominated by γδ T cells that produced TNFα and IFNγ. Furthermore, we found that in individuals infected with Mtb, γδ T cells proliferated less in response to SM worm antigens and had higher IL-4 production compared to naïve controls. Together these data demonstrate that γδ T cells respond robustly to SM worm antigens and that Mtb infection modifies the γδ T cell response to SM.

Schistosomiasis, a disease caused by parasitic helminths including Schistosoma mansoni (SM), affects hundreds of millions of people globally. SM undergoes a complex life cycle within humans resulting in adult worm pairs that release eggs into the circulatory system. The human immune response to SM, especially to adult worms, is not well characterized. In addition, the impact of co-infections, which are common in SM endemic regions, on the immune response to SM is unknown. In this study, we first sought to characterize the T cell response to different stages of the SM life cycle. We next evaluated whether T cell responses to SM were altered in the setting of co-infection with Mycobacterium tuberculosis, the bacteria that causes tuberculosis. We determined that human T cell responses to SM adult worm antigen are more robust than to SM egg antigen. This response is dominated by a non-classical T cell subset of γδ T cells producing IFNγ and TNFα. Lastly, we found that the ability of γδ T cells to proliferate in response to SM worm was lower in individuals with tuberculosis compared to naïve controls. This study provides novel insights into the immune response to SM and how tuberculosis may impair SM immunity.

Identification of the Ligands of TCRγδ by Screening the Immune Repertoire of γδT Cells From Patients With Tuberculosis

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) infection is a serious threat to human health. γδT cells, which are characterized by major histocompatibility complex (MHC) non-restriction, are rapidly activated and initiate anti-infectious immune responses in the early stages of Mtb infection. However, the mechanism underlying the recognition of Mtb by γδT cells remains unclear. In this study, we characterized the pattern of the human T-cell receptor (TCR) γδ complementary determinant region 3 (CDR3) repertoire in TB patients by using high-throughput immune repertoire sequencing. The results showed that the diversity of CDR3δ was significantly reduced and that the frequency of different gene fragments (V/J), particularly the V-segment of the δ-chain, was substantially altered, which indicate that TB infection-related γδT cells, especially the δ genes, were activated and amplified in TB patients. Then, we screened the Mtb-associated epitopes/proteins recognized by γδT cells using an Mtb proteome chip with dominant CDR3δ peptides as probes. We identified the Mtb protein Rv0002 as a potential ligand capable of stimulating the activation and proliferation of γδT cells. Our findings provide a further understanding of the mechanisms underlying γδT cell-mediated immunity against Mtb infection.

Bacteria-Host Interactions in Multiple Sclerosis

Multiple sclerosis (MS) is caused by a complex interaction of genetic and environmental factors. Numerous causative factors have been identified that play a role in MS, including exposure to bacteria. Mycobacteria, Chlamydia pneumoniae, Helicobacter pylori, and other bacteria have been proposed as risk factors for MS with different mechanisms of action. Conversely, some pathogens may have a protective effect on its etiology. In terms of acquired immunity, molecular mimicry has been hypothesized as the mechanism by which bacterial structures such as DNA, the cell wall, and intracytoplasmic components can activate autoreactive T cells or produce autoantibodies in certain host genetic backgrounds of susceptible individuals. In innate immunity, Toll-like receptors play an essential role in combating invading bacteria, and their activation leads to the release of cytokines or chemokines that mediate effective adaptive immune responses. These receptors may also be involved in central nervous system autoimmunity, and their contribution depends on the infection site and on the pathogen. We have reviewed the current knowledge of the influence of bacteria on MS development, emphasizing the potential mechanisms of action by which bacteria affect MS initiation and/or progression.

Immunological responses of European badgers (Meles Meles) to infection with Mycobacterium bovis

Mycobacterium bovis is the main cause of bovine tuberculosis and its eradication is proving difficult in many countries because of wildlife reservoirs, including European badgers (Meles meles) in the UK Ireland. Following the development of badger specific immunological reagents, many studies have shown that some aspects of the cellular and serological immune responses of badgers to virulent M. bovis and the attenuated M. bovis BCG (Bacille of Calmette and Guérin) strain are similar to those seen in other animal hosts infected with M. bovis. However, badgers also appear to have developed specific immunological responses to M. bovis infection which may be associated with mild inflammatory responses. Badgers may therefore represent an interesting natural host for M. bovis that can provide a more thorough understanding of efficient immunological responses to tuberculosis.

Insights into Local Tumor Microenvironment Immune Factors Associated with Regression of Cutaneous Melanoma Metastases by Mycobacterium bovis Bacille Calmette-Guérin

Mycobacterium bovis bacille Calmette–Guérin (BCG) is listed as an intralesional (IL) therapeutic option for inoperable stage III in-transit melanoma in the National Comprehensive Cancer Network Guidelines. Although the mechanism is unknown, others have reported up to 50% regression of injected lesions, and 17% regression of uninjected lesions in immunocompetent patients after direct injection of BCG into metastatic melanoma lesions in the skin. BCG and other mycobacteria express ligands capable of stimulating the γ9δ2 T cells. Therefore, we hypothesized that γ9δ2 T cells play a role in promoting BCG-mediated antitumor immunity in patients treated with IL-BCG for in-transit cutaneous melanoma metastases. Indeed, we found γ9δ2 T cell infiltration in melanoma skin lesions during the course of IL-BCG treatment. Gene expression analysis revealed that BCG injection elicits the expression of a vast array of chemokines in tumor lesions, including strong expression of CXCL9, 10, and 11, a set of chemokines that attract T cells expressing the CXCR3 chemokine receptor. In corroboration with our hypothesis, approximately 85% of γδ T cells express high levels of CXCR3 on their surface. Importantly, the injected tumor lesions also express genes whose protein products are the antigenic ligands for γδ T cells (BTN3A1 and MICB), and the cytokines that are the typical products of activated γδ T cells. Interestingly, we also found that γδ T cells infiltrate the regressed lesions that did not receive BCG injections. Our study suggests that γ9δ2 T cells may contribute to melanoma regression induced by IL-BCG treatment.

Characterization of CD4/CD8+ αβ and Vγ2Vδ2+ T cells in HIV-negative individuals with different Mycobacterium tuberculosis infection statuses

BACKGROUND

The immune responses of T cell subsets among patients with different Mycobacterium tuberculosis (M.tb) infection statuses [i.e., active tuberculosis (ATB), latent tuberculosis infection (LTBI) and non-infection (healthy control, HC)] have not been fully elucidated in HIV-negative individuals. Specifically, data are limiting in high tuberculosis epidemic regions in China. To investigate the distributions and functions of T cell subsets (i.e., CD3+, CD4+, CD8+ αβ and Vγ2Vδ2+ T cells) in HIV-negative subjects with different M.tb infection statuses, we conducted a case-control study that enrolled 125 participants, including ATB patients (n = 46), LTBI subjects (n = 34), and HC (n = 45).

RESULTS

An IFN-γ release assay (IGRA) was employed to screen LTBI subjects. Whole blood cell surface staining and flow cytometry were used to detect phenotypic distributions of T cells in the peripheral blood mononuclear cells (PBMCs) and tuberculous pleural fluid mononuclear cells (PFMCs). PPD and the phosphorylated antigen HMBPP were employed as stimulators for the detection of M.tb antigen-specific T cell functions via intracellular cytokine staining (ICS). The absolute numbers of T cell subsets, including CD3+ CD4+, CD3+ CD8+ αβ and Vγ2Vδ2+ T cells, were significantly reduced in active tuberculosis compared with latent tuberculosis or the healthy controls. Importantly, PPD-specific CD3+ CD4+ and CD3+ CD8+ αβ T cells and HMBPP-specific Vγ2Vδ2+ T cells in ATB patients were also significantly reduced compared to the LTBI/HC subjects (P<0.05). In contrast, the proportion of CD4+ T cells in PFMCs was higher compared to PBMCs, while CD8+ and Vγ2Vδ2+ T cells in PFMCs were lower compared to PBMCs (all P < 0.05). PPD-specific CD4+ T cells predominated among CD3+ T cells in PFMCs.

CONCLUSIONS

Cellular immune responses are impaired in ATB patients. Antigen-specific CD4+ T cell may migrate from the periphery to the lesion site, where they exert anti-tuberculosis functions.

Dynamics of immune effector mechanisms during infection with Mycobacterium avium in C57BL/6 mice

Opportunistic infections with non-tuberculous mycobacteria such as Mycobacterium avium are receiving renewed attention because of increased incidence and difficulties in treatment. As for other mycobacterial infections, a still poorly understood collaboration of different immune effector mechanisms is required to confer protective immunity. Here we have characterized the interplay of innate and adaptive immune effector mechanisms contributing to containment in a mouse infection model using virulent M. avium strain 104 in C57BL/6 mice. M. avium caused chronic infection in mice, as shown by sustained organ bacterial load. In the liver, bacteria were contained in granuloma-like structures that could be defined morphologically by expression of the antibacterial innate effector protein Lipocalin 2 in the adjoining hepatocytes and infiltrating neutrophils, possibly contributing to containment. Circulatory anti-mycobacterial antibodies steadily increased throughout infection and were primarily of the IgM isotype. Highest levels of interferon-γ were found in infected liver, spleen and serum of mice approximately 2 weeks post infection and coincided with a halt in organ bacterial growth. In contrast, expression of tumour necrosis factor was surprisingly low in spleen compared with liver. We did not detect interleukin-17 in infected organs or M. avium-specific T helper 17 cells, suggesting a minor role for T helper 17 cells in this model. A transient and relative decrease in regulatory T cell numbers was seen in spleens. This detailed characterization of M. avium infection in C57BL/6 mice may provide a basis for future studies aimed at gaining better insight into mechanisms leading to containment of infections with non-tuberculous mycobacteria.

Role of MHC class Ib molecule, H2-M3 in host immunity against tuberculosis

The MHC class I family comprises both classical (class Ia) and non-classical (class Ib) members. While the prime function of classical MHC class I molecules (MHC class Ia) is to present peptide antigens to pathogen-specific cytotoxic T cells, non-classical MHC-I (MHC class Ib) antigens perform diverse array of functions in both innate and adaptive immunity. Vaccines against intracellular pathogens such as Mycobacterium tuberculosis need to induce strong cellular immune responses. Recent studies have shown that MHC class I molecules play an important role in the protective immune response to M. tuberculosis infection. Both MHC Ia-restricted and MHC class Ib-restricted M. tuberculosis -reactive CD8(+) T cells have been identified in humans and mice, but their relative contributions to immunity is still uncertain. Unlike MHC class Ia-restricted CD8(+) T cells, MHC class Ib-restricted CD8(+) T cells are constitutively activated in naive animals and respond rapidly to infection challenge, hence filling the temporal gap between innate and adaptive immunity. The present review article summarizes the general host immunity against M. tuberculosis infection highlighting the possible role of MHC class Ib molecule, H2-M3 and their ligands (N-formylated peptides) in protection against tuberculosis.

Immune response to Streptococcus pneumoniae in asthma patients: comparison between stable situation and exacerbation

In Argentina, more than 3 million people suffer from asthma, with numbers rising. When asthma patients acquire viral infections which, in turn, trigger the asthmatic response, they may develop subsequent bacterial infections, mainly by Streptococcus (S.) pneumoniae. This encapsulated Gram(+) bacterium has been considered historically a T cell-independent antigen. Nevertheless, several papers describe the role of T cells in the immune response to S. pneumoniae. We evaluated the response to S. pneumoniae and compared it to the response to Mycobacterium (M.) tuberculosis, a different type of bacterium that requires a T helper type 1 (Th1) response, in cells from atopic asthmatic children, to compare parameters for the same individual under exacerbation and in a stable situation whenever possible. We studied asthma patients and a control group of age-matched children, evaluating cell populations, activation markers and cytokine production by flow cytometry, and cytokine concentration in serum and cell culture supernatants by enzyme-linked immunosorbent assay (ELISA). No differences were observed in γδ T cells for the same patient in either situation, and a tendency to lower percentages of CD4(+) CD25(hi) T cells was observed under stability. A significantly lower production of tumour necrosis factor (TNF)-α and a significantly higher production of interleukin (IL)-5 was observed in asthma patients compared to healthy individuals, but no differences could be observed for IL-4, IL-13 or IL-10. A greater early activation response against M. tuberculosis, compared to S. pneumoniae, was observed in the asthmatic patients' cells. This may contribute to explaining why these patients frequently acquire infections caused by the latter bacterium and not the former.

Clonal immune responses of Mycobacterium-specific γδ T cells in tuberculous and non-tuberculous tissues during M. tuberculosis infection

BACKGROUND

We previously demonstrated that unvaccinated macaques infected with large-dose M.tuberculosis(Mtb) exhibited delays for pulmonary trafficking of Ag-specific αβ and γδ T effector cells, and developed severe lung tuberculosis(TB) and "secondary" Mtb infection in remote organs such as liver and kidney. Despite delays in lungs, local immunity in remote organs may accumulate since progressive immune activation after pulmonary Mtb infection may allow IFNγ-producing γδ T cells to adequately develop and traffic to lately-infected remote organs. As initial efforts to test this hypothesis, we comparatively examined TCR repertoire/clonality, tissue trafficking and effector function of Vγ2Vδ2 T cells in lung with severe TB and in liver/kidney without apparent TB.

METHODOLOGY/PRINCIPAL FINDINGS

We utilized conventional infection-immunity approaches in macaque TB model, and employed our decades-long expertise for TCR repertoire analyses. TCR repertoires in Vγ2Vδ2 T-cell subpopulation were broad during primary Mtb infection as most TCR clones found in lymphoid system, lung, kidney and liver were distinct. Polyclonally-expanded Vγ2Vδ2 T-cell clones from lymphoid tissues appeared to distribute and localize in lung TB granuloms at the endpoint after Mtb infection by aerosol. Interestingly, some TCR clones appeared to be more predominant than others in lymphocytes from liver or kidney without apparent TB lesions. TCR CDR3 spetratyping revealed such clonal dominance, and the clonal dominance of expanded Vγ2Vδ2 T cells in kidney/liver tissues was associated with undetectable or low-level TB burdens. Furthermore, Vγ2Vδ2 T cells from tissue compartments could mount effector function for producing anti-mycobacterium cytokine.

CONCLUSION

We were the first to demonstrate clonal immune responses of mycobacterium-specific Vγ2Vδ2 T cells in the lymphoid system, heavily-infected lungs and lately subtly-infected kidneys or livers during primary Mtb infection. While clonally-expanded Vγ2Vδ2 T cells accumulated in lately-infected kidneys/livers without apparent TB lesions, TB burdens or lesions appeared to impact TCR repertoires and tissue trafficking patterns of activated Vγ2Vδ2 T cells.

Modulation of T cell cytokine production by miR-144* with elevated expression in patients with pulmonary tuberculosis

microRNAs have a critical role in regulating innate and adaptive immunity. To understand whether microRNAs play roles in regulating immune responses to Mycobacterium tuberculosis infection in humans, microRNA expression profiling was performed in PBMCs from pulmonary tuberculosis patients and healthy controls. Analysis of expression profiles showed that expression of 30 microRNAs was significantly altered during active TB as compared with healthy controls, 28 microRNAs were up-regulated and 2 microRNAs down-regulated. miR-144* was one of the microRNAs that were overexpressed in active TB patients. Real-time RT-PCR analysis showed that miR-144* was mainly expressed in T cells. Transfection of T cells with miR-144* precursor demonstrated that miR-144* could inhibit TNF-α and IFN-γ production and T cell proliferation. It is concluded that miR-144* might involve in regulation of anti-TB immunity through modification of cytokine production and cell proliferation of T cells.

Elevated expression of Tim-3 on CD8 T cells correlates with disease severity of pulmonary tuberculosis

OBJECTIVES

T cell immunoglobulin and mucin domain-containing molecule 3 (Tim-3) plays an important role in regulating T cell responses and induction of peripheral tolerance. In this study, the association of Tim-3 with active pulmonary tuberculosis (TB) was investigated.

METHODS

Tim-3 expression on CD8 T cells and its influence on production of effector molecules and proliferation of CD8 T cells were examined.

RESULTS

Pulmonary TB patients had significantly elevated Tim-3 expression on total CD8 T cells (P < 0.0001) and on antigen-specific CD8 T cells (P = 0.0028) compared with tuberculin-positive healthy controls. The expression of Tim-3 on CD8 T cells was significantly higher in smear/culture-positive TB patients than smear/culture-negative TB patients (P < 0.0001). Tim-3 expressing CD8 T cells had reduced production of IFN-γ, decreased degranulation and lower proliferation in response to Mycobacterium tuberculosis antigen stimulation. Blocking of Tim-3 signaling led to significantly increased production of IFN-γ.

CONCLUSIONS

The elevated expression of Tim-3 on CD8 T cells correlates with functional defects of CD8 T cells and disease severity of pulmonary TB.

Genome-wide screen for Mycobacterium tuberculosis genes that regulate host immunity

In spite of its highly immunogenic properties, Mycobacterium tuberculosis (Mtb) establishes persistent infection in otherwise healthy individuals, making it one of the most widespread and deadly human pathogens. Mtb's prolonged survival may reflect production of microbial factors that prevent even more vigorous immunity (quantitative effect) or that divert the immune response to a non-sterilizing mode (qualitative effect). Disruption of Mtb genes has produced a list of several dozen candidate immunomodulatory factors. Here we used robotic fluorescence microscopy to screen 10,100 loss-of-function transposon mutants of Mtb for their impact on the expression of promoter-reporter constructs for 12 host immune response genes in a mouse macrophage cell line. The screen identified 364 candidate immunoregulatory genes. To illustrate the utility of the candidate list, we confirmed the impact of 35 Mtb mutant strains on expression of endogenous immune response genes in primary macrophages. Detailed analysis focused on a strain of Mtb in which a transposon disrupts Rv0431, a gene encoding a conserved protein of unknown function. This mutant elicited much more macrophage TNFα, IL-12p40 and IL-6 in vitro than wild type Mtb, and was attenuated in the mouse. The mutant list provides a platform for exploring the immunobiology of tuberculosis, for example, by combining immunoregulatory mutations in a candidate vaccine strain.

Aerosol vaccines for tuberculosis: a fine line between protection and pathology

Pulmonary delivery of vaccines against airborne infection is being investigated worldwide, but there is limited effort directed at developing inhaled vaccines for tuberculosis (TB). This review addresses some of the challenges confronting vaccine development for TB and attempts to link these challenges to the promises of mucosal immunity offered by pulmonary delivery. There are several approaches working toward this goal including subunit vaccines, recombinant strains, a novel vaccine strain Mycobacterium w, and DNA vaccine approaches. While it is clear that lung-resident adaptive immunity is an attainable goal, vaccine platforms must ensure that damage to the lung is limited during both vaccination and when memory cells respond to pathogenic infection.

A novel mechanism of soluble HLA-G mediated immune modulation: downregulation of T cell chemokine receptor expression and impairment of chemotaxis

Background

In recent years, many immunoregulatory functions have been ascribed to soluble HLA-G (sHLA-G). Since chemotaxis is crucial for an efficient immune response, we have investigated for the first time the effects of sHLA-G on chemokine receptor expression and function in different human T cell populations.

Methodology/Principal Findings

T cell populations isolated from peripheral blood were stimulated in the presence or absence of sHLA-G. Chemokine receptors expression was evaluated by flow cytometry. sHLA-G downregulated expression of i) CCR2, CXCR3 and CXCR5 in CD4⁺ T cells, ii) CXCR3 in CD8⁺ T cells, iii) CXCR3 in Th1 clones iv) CXCR3 in TCR Vδ2γ9 T cells, and upregulated CXCR4 expression in TCR Vδ2γ9 T cells. sHLA-G inhibited in vitro chemotaxis of i) CD4⁺ T cells towards CCL2, CCL8, CXCL10 and CXCL11, ii) CD8⁺ T cells towards CXCL10 and CXCL11, iii) Th1 clones towards CXCL10, and iv) TCR Vδ2γ9 T cells towards CXCL10 and CXCL11. Downregulation of CXCR3 expression on CD4+ T cells by sHLA-G was partially reverted by adding a blocking antibody against ILT2/CD85j, a receptor for sHLA-G, suggesting that sHLA-G downregulated chemokine receptor expression mainly through the interaction with ILT2/CD85j. Follicular helper T cells (T_FH) were isolated from human tonsils and stimulated as described above. sHLA-G impaired CXCR5 expression in T_FH and chemotaxis of the latter cells towards CXCL13. Moreover, sHLA-G expression was detected in tonsils by immunohistochemistry, suggesting a role of sHLA-G in local control of T_FH cell chemotaxis. Intracellular pathways were investigated by Western Blot analysis on total extracts from CD4+ T cells. Phosphorylation of Stat5, p70 s6k, β-arrestin and SHP2 was modulated by sHLA-G treatment.

Conclusions/Significance

Our data demonstrated that sHLA-G impairs expression and functionality of different chemokine receptors in T cells. These findings delineate a novel mechanism whereby sHLA-G modulates T cell recruitment in physiological and pathological conditions.

Differentiation, distribution and gammadelta T cell-driven regulation of IL-22-producing T cells in tuberculosis

Differentiation, distribution and immune regulation of human IL-22-producing T cells in infections remain unknown. Here, we demonstrated in a nonhuman primate model that M. tuberculosis infection resulted in apparent increases in numbers of T cells capable of producing IL-22 de novo without in vitro Ag stimulation, and drove distribution of these cells more dramatically in lungs than in blood and lymphoid tissues. Consistently, IL-22-producing T cells were visualized in situ in lung tuberculosis (TB) granulomas by confocal microscopy and immunohistochemistry, indicating that mature IL-22-producing T cells were present in TB granuloma. Surprisingly, phosphoantigen HMBPP activation of Vgamma2Vdelta2 T cells down-regulated the capability of T cells to produce IL-22 de novo in lymphocytes from blood, lung/BAL fluid, spleen and lymph node. Up-regulation of IFNgamma-producing Vgamma2Vdelta2 T effector cells after HMBPP stimulation coincided with the down-regulated capacity of these T cells to produce IL-22 de novo. Importantly, anti-IFNgamma neutralizing Ab treatment reversed the HMBPP-mediated down-regulation effect on IL-22-producing T cells, suggesting that Vgamma2Vdelta2 T-cell-driven IFNgamma-networking function was the mechanism underlying the HMBPP-mediated down-regulation of the capability of T cells to produce IL-22. These novel findings raise the possibility to ultimately investigate the function of IL-22 producing T cells and to target Vgamma2Vdelta2 T cells for balancing potentially hyper-activating IL-22-producing T cells in severe TB.

Gamma-delta T cell subsets are differentially associated with granuloma development and organization in a bovine model of mycobacterial disease

The characteristic lesion in bovine tuberculosis is well-organized respiratory granulomas. This is typically associated with a strong T-helper 1 biased cell-mediated immune response and eventual containment of the infection. In bovine paratuberculosis, the classic lesion is unorganized granulomatous intestinal inflammation. Clinical paratuberculosis is associated with a T-helper 2 biased humoral immune response and eventual death because of inability of the host to contain the infection. Recent reports have suggested that gamma-delta (gammadelta) T cells play a significant role in granuloma development and/or maintenance during initial stages of infection and may influence the subsequent adaptive immune response. The objective of this study was to use an in vivo bovine model to evaluate gammadelta T cells during the early host immune response to mycobacterial infection. We used immunofluorescent staining, hyperspectral microscopy, and computerized assisted morphometry to evaluate staining and distribution of gammadelta T cells during development of organized and unorganized granulomas. Our data suggest that bovine gammadelta T cell subsets are differentially recruited to early infection sites, and may be instrumental during the initial antimycobacterial host immune response as well as for granuloma organization.

Evasion and subversion of antigen presentation by Mycobacterium tuberculosis

Mycobacterium tuberculosis is one of the most successful of human pathogens and has acquired the ability to establish latent or progressive infection and persist even in the presence of a fully functioning immune system. The ability of M. tuberculosis to avoid immune-mediated clearance is likely to reflect a highly evolved and coordinated program of immune evasion strategies, including some that interfere with antigen presentation to prevent or alter the quality of T-cell responses. Here, we review an extensive array of published studies supporting the view that antigen presentation pathways are targeted at many points by pathogenic mycobacteria. These studies show the multiple potential mechanisms by which M. tuberculosis may actively inhibit, subvert or otherwise modulate antigen presentation by major histocompatibility complex class I, class II and CD1 molecules. Unraveling the mechanisms by which M. tuberculosis evades or modulates antigen presentation is of critical importance for the development of more effective new vaccines based on live attenuated mycobacterial strains.

CD4+ CD25(high) Foxp3+ regulatory T cells downregulate human Vdelta2+ T-lymphocyte function triggered by anti-CD3 or phosphoantigen

Vdelta2+ T cells, the major circulating T-cell receptor-gammadelta-positive (TCR-gammadelta+) T-cell subset in healthy adults, are involved in immunity against many microbial pathogens including Mycobacterium tuberculosis. Vdelta2+ T cells recognize small phosphorylated metabolites (phosphoantigens), expand in response to whole M. tuberculosis bacilli, and complement the protective functions of CD4+ T cells. CD4+ CD25(high) Foxp3+ T cells (Tregs) comprise 5-10% of circulating T cells and are increased in patients with active tuberculosis (TB). We investigated whether, in addition to their known role in suppressing TCR-alphabeta+ lymphocytes, Tregs suppress Vdelta2+ T-cell function. We found that depletion of Tregs from peripheral blood mononuclear cells increased Vdelta2+ T-cell expansion in response to M. tuberculosis (H37Ra) in tuberculin-skin-test-positive donors. We developed a suppression assay with fluorescence-activated cell sorting-purified Tregs and Vdelta2+ T cells by coincubating the two cell types at a 1 : 1 ratio. The Tregs partially suppressed interferon-gamma secretion by Vdelta2+ T cells in response to anti-CD3 monoclonal antibody plus interleukin-2 (IL-2). In addition, Tregs downregulated the Vdelta2+ T-cell interferon-gamma responses induced by phosphoantigen (BrHPP) and IL-2. Under the latter conditions there was no TCR stimulus for Tregs and therefore IL-2 probably triggered suppressor activity. Addition of purified protein derivative (PPD) increased the suppression of Vdelta2+ T cells, suggesting that PPD activated antigen-specific Tregs. Our study provides evidence that Tregs suppress both anti-CD3 and antigen-driven Vdelta2+ T-cell activation. Antigen-specific Tregs may therefore contribute to the Vdelta2+ T-cell functional deficiencies observed in TB.

Potent immune responses of Ag-specific Vgamma2Vdelta2+ T cells and CD8+ T cells associated with latent stage of Mycobacterium tuberculosis coinfection in HIV-1-infected humans

OBJECTIVE

To investigate immune responses of peptide-specific CD4+ and CD8+ T cells, and nonpeptide-specific Vgamma2Vdelta2+ T cells during clinical quiescence of latent Mycobacterium tuberculosis coinfection in HIV-1-infected humans.

METHODS

One hundred HIV-1-infected individuals who had HIV infection only [HIV+tuberculosis-(TB-)], latent Mycobacterium tuberculosis coinfection (HIV + LTB), or active tuberculosis (HIV + TB) were recruited to measure mycobacterium purified protein derivative (PPD)-specific IFNgamma+ CD4+ and CD8+ T cells, and phosphoantigen HMBPP-specific IFNgamma+ Vgamma2Vdelta2+ T cells using enzyme-linked immunospot and intracellular cytokine staining assays.

RESULTS

Both HIV + TB and HIV + LTB groups had low levels of PPD-specific IFNgamma+ CD4+ T cells regardless of CD4+ peripheral blood lymphocytes counts. However, numbers of PPD-specific IFNgamma+ CD8+ T cells in the HIV + LTB group were significantly greater than those in the HIV + TB group. Surprisingly, numbers of phosphoantigen hydroxy-3-methyl-but-2-enyl pyrophosphate-specific IFNgamma+ Vgamma2Vdelta2+ T cells in the HIV + LTB group were much greater than those in the HIV + TB group (P < 0.001). This difference was present in the subgroups of HIV + LTB whatever the levels of CD4+ T-cell counts more than 200/microl or less than 200/microl. Numbers of hydroxy-3-methyl-but-2-enyl pyrophosphate-specific IFNgamma+ Vgamma2Vdelta2+ T cells were even five times greater than those of PPD-specific IFNgamma+ CD8 T cells within the HIV + LTB group.

CONCLUSION

Potent immune responses of hydroxy-3-methyl-but-2-enyl pyrophosphate-specific IFNgamma+ Vgamma2Vdelta2+ T cells and PPD-specific IFNgamma+ CD8+ T cells were detected in HIV + LTB persons but not HIV + TB patients. The robust immune responses of Vgamma2Vdelta2+ and CD8+ T effector cells were associated with the latent stage of Mycobacterium tuberculosis coinfection in HIV-1-infected humans.

Mycobacterial lipopeptides elicit CD4+ CTLs in Mycobacterium tuberculosis-infected humans

In searching for immunogenic molecules with the potential to induce protective immune responses against tuberculosis, we developed an ex vivo model to study frequency, phenotype, and effector functions of human T lymphocytes recognizing hydrophobic Ags of Mycobacterium tuberculosis (M.Tb). To obtain unbiased results, we characterized T lymphocytes responding to a crude cell wall extract (chloroform methanol extract of M.Tb (M.Tb-CME)) containing a broad spectrum of mycobacterial glycolipids and lipopeptides. A significant proportion of T lymphocytes recognized M.Tb-CME (290 IFN-gamma+ T cells/10(5) PBMCs) and developed to effector memory cells as determined by the expression of CD45RO and the chemokine receptors CXCR3 and CCR5. Expanded lymphocytes fulfilled all criteria required for an efficient immune response against tuberculosis: 1) release of macrophage-activating Th1 cytokines and chemokines required for the spatial organization of local immune responses, 2) cytolytic activity against Ag-pulsed macrophages, and 3) recognition of infected macrophages and killing of the intracellular bacteria. Phenotypically, M.Tb-CME-expanded cells were CD4+ and MHC class II restricted, challenging current concepts that cytotoxic and antimicrobial effector cells are restricted to the CD8+ T cell subset. Pretreatment of M.Tb-CME with protease or chemical delipidation abrogated the biological activity, suggesting that responses were directed toward mycobacterial lipopeptides. These findings suggest that lipidated peptides are presented by M.Tb-infected macrophages and elicit CD4+ cytolytic and antimicrobial T lymphocytes. Our data support an emerging concept to include hydrophobic microbial Ags in vaccines against tuberculosis.

CD4+ CD25+ Treg cells inhibit human memory gammadelta T cells to produce IFN-gamma in response to M tuberculosis antigen ESAT-6

Gammadelta T cells play an important role in innate immunity against infections; however, the regulation of these cells remains largely unknown. In the present study, we show that ESAT-6, an antigen of Mycobacterium tuberculosis, induces IFN-gamma secretion by human gammadelta T cells. In addition, ESAT-6 also induces the activation and proliferation of gammadelta T cells. Phenotypic analysis indicates that IFN-gamma-producing gammadelta T cells are mainly effector memory cells with the surface phenotype of CD45RA(-)CD62L(-)CCR7(-). These results were further confirmed by the fact that naive gammadelta T cells from cord blood did not produce IFN-gamma in response to ESAT-6. Further studies indicated that stimulation with ESAT-6 directly induced purified gammadelta T cells to produce IFN-gamma, independent of both antigen-presenting cells and CD4(+) T cells. Unexpectedly, depletion of CD4(+) T cells markedly enhanced IFN-gamma production by gammadelta T cells, indicating that CD4(+) T cells regulate the response of gammadelta T cells. Importantly, CD4(+)CD25(+) T regulatory (Treg) cells but not CD4(+)CD25(-) T cells significantly inhibited IFN-gamma production by gammadelta T cells. Taken together, these data demonstrate for the first time that Treg cells can play an important role in the regulation of immune responses of antigen-specific human memory gammadelta T cells.

Immune distribution and localization of phosphoantigen-specific Vgamma2Vdelta2 T cells in lymphoid and nonlymphoid tissues in Mycobacterium tuberculosis infection

Little is known about the immune distribution and localization of antigen-specific T cells in mucosal interfaces of tissues/organs during infection of humans. In this study, we made use of a macaque model of Mycobacterium tuberculosis infection to assess phosphoantigen-specific Vgamma2Vdelta2 T cells regarding their tissue distribution, anatomical localization, and correlation with the presence or absence of tuberculosis (TB) lesions in lymphoid and nonlymphoid organs/tissues in the progression of severe pulmonary TB. Progression of pulmonary M. tuberculosis infection generated diverse distribution patterns of Vgamma2Vdelta2 T cells, with remarkable accumulation of these cells in lungs, bronchial lymph nodes, spleens, and remote nonlymphoid organs but not in blood. Increased numbers of Vgamma2Vdelta2 T cells in tissues were associated with M. tuberculosis infection but were independent of the severity of TB lesions. In lungs with apparent TB lesions, Vgamma2Vdelta2 T cells were present within TB granulomas. In extrathoracic organs, Vgamma2Vdelta2 T cells were localized in the interstitial compartment of nonlymphoid tissues, and the interstitial localization was present despite the absence of detectable TB lesions. Finally, Vgamma2Vdelta2 T cells accumulated in tissues appeared to possess cytokine production function, since granzyme B was detectable in the gammadelta T cells present within granulomas. Thus, clonally expanded Vgamma2Vdelta2 T cells appeared to undergo trans-endothelial migration, interstitial localization, and granuloma infiltration as immune responses to M. tuberculosis infection.

Immune factors and immunoregulation in tuberculosis

Pathogens causing tuberculosis and other chronic infectious diseases of major public health importance commonly have complex mechanisms involved in their persistence in the host despite specific and sometimes strong immune responses. These diseases are also associated with the lack of efficient vaccines, difficult therapeutics and a high mortality rate among susceptible individuals. Here, we will review features of the host immune response that contribute to the occurrence of disease. In addition, we propose that the immune responses observed in tuberculosis cannot be interpreted solely on the basis of a Th1-Th2 counter-regulatory paradigm since there is growing evidence that natural regulatory T cells may play an important role in the regulation of host immune responses against Mycobacterium tuberculosis. Thus, the development of more effective vaccines against this bacterial disease should take into account the role of natural regulatory T cells in the progression to severe disease and persistence of infection. Finally, new treatments based on manipulation of regulatory T cells should be investigated.

Impaired expression of perforin and granulysin in CD8+ T cells at the site of infection in human chronic pulmonary tuberculosis

Protective immunity in tuberculosis is dependent on the coordinated release of cytolytic effector molecules from effector T cells and the subsequent granule-associated killing of infected target cells. In this study, we investigated the expression of cytolytic (perforin and granzyme A) and antimicrobial (granulysin) molecules at the single-cell level in cryopreserved lung tissue from patients with chronic, progressive tuberculosis disease. Quantification of protein-expressing cells was performed by in situ imaging, while mRNA levels in the infected tissue were analyzed by real-time PCR. Persistent inflammation, including excessive expression of inducible nitric oxide synthase in CD68+ macrophages and significant infiltration of CD3+, CD8+ and CD4+ T cells, was evident in tuberculosis lesions in all patients. However, despite the accumulation of CD3+ T cells, perforin- and granulysin-expressing CD3+ T cells were detected at two- to threefold-lower ratios in the tuberculosis lesions than in distal lung parenchyma and uninfected control lungs, respectively. This was evident at both the protein and mRNA levels. Moreover, perforin- and granulysin-expressing CD8+ T cells were scarce in individual granulomas within the tuberculosis lesions. In contrast, significant up-regulation of granzyme A-expressing CD3+ T cells was evident in the lesions from all patients. Confocal microscopy revealed coexpression of perforin and granulysin, primarily in CD8+ T cells; however, this expression was lower in the tuberculosis lesions. These findings suggest that symptomatic, chronic tuberculosis disease is associated with insufficient up-regulation of perforin and granulysin coexpression in CD8+ T cells at the local site of infection.

Host innate immune response to Mycobacterium tuberculosis

This review focuses on recent progress in our understanding of Mycobacterium tuberculosis survival in macrophages, the interaction of M. tuberculosis with Toll-like receptors (TLRs) and the establishment of the link between innate and adaptive immunity, and TLRs and interferon-gamma-mediated antimicrobial pathways in macrophages. We also propose a paradigm that TLR2 signaling regulates the magnitude of the host Th1 response leading to either M. tuberculosis persistence and latent infection or replication and disease.

Crystal structures of human IPP isomerase: new insights into the catalytic mechanism

Type I isopentenyl diphosphate (IPP): dimethylally diphosphate (DMAPP) isomerase is an essential enzyme in human isoprenoid biosynthetic pathway. It catalyzes isomerization of the carbon-carbon double bonds in IPP and DMAPP, which are the basic building blocks for the subsequent biosynthesis. We have determined two crystal structures of human IPP isomerase I (hIPPI) under different crystallization conditions. High similarity between structures of human and Escherichia coli IPP isomerases proves the conserved catalytic mechanism. Unexpectedly, one of the hIPPI structures contains a natural substrate analog ethanol amine pyrophosphate (EAPP). Based on this structure, a water molecule is proposed to be the direct proton donor for IPP and different conformations of IPP and DMAPP bound in the enzyme are also proposed. In addition, structures of human IPPI show a flexible N-terminal alpha-helix covering the active pocket and blocking the entrance, which is absent in E. coli IPPI. Besides, the active site conformation is not the same in the two hIPPI structures. Such difference leads to a hypothesis that substrate binding induces conformational change in the active site. The inhibition mechanism of high Mn(2+) concentrations is also discussed.