Mycobacterium tuberculosis-specific memory NKT cells in patients with tuberculous pleurisy

Heterogeneity of OAS family expression in tuberculosis and the impact of different sample selection: a comprehensive analysis

The 2'-5' oligoadenylate synthetase (OAS)family, comprising OAS1, OAS2, OAS3, and OASL, has been shown to participate in the host immune response against Mycobacterium tuberculosis (Mtb). However, their expression profiles in tuberculosis (TB) remain inconsistent. In two TB-related datasets, the OAS family exhibits contrasting expression trends. To further investigate, we examined the expression of the OAS family in whole blood, peripheral blood mononuclear cells (PBMC), and pleural fluid mononuclear cells (PFMC) as study samples, focusing on pulmonary tuberculosis (PTB) and tuberculous pleuritis (TPE). The results revealed differing expression patterns of the OAS family in the two diseases. In PFMC samples from TPE patients, the OAS family showed overall upregulation. Additionally, matched samples from nine TPE patients indicated overlapping expression of the OAS family in both PBMC and PFMC samples.

Diagnostic value of IFN-gamma in tuberculous pleural effusion

BACKGROUND

Simple, rapid, and accurate diagnosis of tuberculous pleural effusion (TPE) remains challenging. This study aimed to determine the accuracy of IFN-γ in diagnosing TPE.

METHODS

We quantified the expression of interferon-gamma (IFN-γ) in blood (B), adenosine deaminase (ADA), and IFN-γ in pleural effusions (PE) from 25 TPE patients and 31 non-TPE patients using a combination of immunological assays and flow cytometric analysis. The diagnostic performance of these three biomarkers was evaluated using receiver operating characteristic (ROC) curves.

RESULTS

We found that IFN-γ levels in blood and pleural fluid were higher in the TPE group than in the non-TPE group. The mean concentration of IFN-γ in pleural fluid of the TPE group was 3140.90 (1817.94, 6611.05) pg/mL, while that of the non-TPE group was 4.91 (0.69, 8.6) pg/mL), and the difference was statistically significant (z = 6.39, P < 0.001). The mean blood IFN-γ was 40.19 (16.45, 59.08) pg/mL in the TPE group and 2.76 (1.96, 6.02) pg/mL in the non-TPE group, which was statistically different (z = 5.12, P < 0.001). The area under the ROC curve (AUC) for pleural fluid IFN-γ, blood IFN-γ, and ADA were 0.999 (95 % CI: 0.994-1.00), 0.901 (95 % CI: 0.798-1.00) and 0.996 (95 % CI: 0.987-1.00), respectively.

CONCLUSION

This study confirms that IFN-γ has high diagnostic validity in patients with TPE and can potentially be an excellent biomarker.

invariant Natural Killer T Cells Modulate the Peritoneal Macrophage Response to Polymicrobial Sepsis

INTRODUCTION

A dysregulated immune system is a major driver of the mortality and long-term morbidity from sepsis. With respect to macrophages, it has been shown that phenotypic changes are critical to effector function in response to acute infections, including intra-abdominal sepsis. Invariant natural killer T cells (iNKT cells) have emerged as potential central regulators of the immune response to a variety of infectious insults. Specifically, various iNKT cell:macrophage interactions have been noted across a spectrum of diseases, including acute events such as sepsis. However, the potential for iNKT cells to affect peritoneal macrophages during an abdominal septic event is as yet unknown.

METHODS

Cecal ligation and puncture (CLP) was performed in both wild type (WT) and invariant natural killer T cell knockout (iNKT-/-) mice. 24 h following CLP or sham operation, peritoneal macrophages were collected for analysis. Analysis of macrophage phenotype and function was undertaken to include analysis of bactericidal activity and cytokine or superoxide production.

RESULTS

Within iNKT-/- mice, a greater degree of intraperitoneal macrophages in response to the sepsis was noted. Compared to WT mice, within iNKT-/- mice, CLP did induce an increase in CD86+ and CD206+, but no difference in CD11b+. Unlike WT mice, intra-abdominal sepsis within iNKT-/- mice induced an increase in Ly6C-int (5.2% versus 14.9%; P < 0.05) and a decrease in Ly6C-high on peritoneal macrophages. Unlike phagocytosis, iNKT cells did not affect macrophage bactericidal activity. Although iNKT cells did not affect interleukin-6 production, iNKT cells did affect IL-10 production and both nitrite and superoxide production from peritoneal macrophages.

CONCLUSIONS

The observations indicate that iNKT cells affect specific phenotypic and functional aspects of peritoneal macrophages during polymicrobial sepsis. Given that pharmacologic agents that affect iNKT cell functioning are currently in clinical trial, these findings may have the potential for translation to critically ill surgical patients with abdominal sepsis.

Natural Killer T and Natural Killer Cell-Based Immunotherapy Strategies Targeting Cancer

Both natural killer T (NKT) and natural killer (NK) cells are innate cytotoxic lymphoid cells that produce inflammatory cytokines and chemokines, and their role in the innate immune response to tumors and microorganisms has been investigated. Especially, emerging evidence has revealed their status and function in the tumor microenvironment (TME) of tumor cells. Some bacteria producing NKT cell ligands have been identified to exert antitumor effects, even in the TME. By contrast, tumor-derived lipids or metabolites may reportedly suppress NKT and NK cells in situ. Since NKT and NK cells recognize stress-inducible molecules or inhibitory molecules on cancer cells, their status or function depends on the balance between inhibitory and activating receptor signals. As a recent strategy in cancer immunotherapy, the mobilization or restoration of endogenous NKT or NK cells by novel vaccines or therapies has become a focus of research. As a new biological evidence, after activation, effector memory-type NKT cells lasted in tumor-bearing models, and NK cell-based immune checkpoint inhibition potentiated the enhancement of NK cell cytotoxicity against cancer cells in preclinical and clinical trials. Furthermore, several new modalities based on the characteristics of NKT and NK cells, including artificial adjuvant vector cells, chimeric antigen receptor-expressing NK or NKT cell therapy, or their combination with immune checkpoint blockade have been developed. This review examines challenges and future directions for improving these therapies.

Effects of BCG vaccination on donor unrestricted T cells in two prospective cohort studies

BACKGROUND

Non-protein antigen classes can be presented to T cells by near-monomorphic antigen-presenting molecules such as CD1, MR1, and butyrophilin 3A1. Such T cells, referred to as donor unrestricted T (DURT) cells, typically express stereotypic T cell receptors. The near-unrestricted nature of DURT cell antigen recognition is of particular interest for vaccine development, and we sought to define the roles of DURT cells, including MR1-restricted MAIT cells, CD1b-restricted glucose monomycolate (GMM)-specific T cells, CD1d-restricted NKT cells, and γδ T cells, in vaccination against Mycobacterium tuberculosis.

METHODS

We compared and characterized DURT cells following primary bacille Calmette-Guerin (BCG) vaccination in a cohort of vaccinated and unvaccinated infants, as well as before and after BCG-revaccination in adults.

FINDINGS

BCG (re)vaccination did not modulate peripheral blood frequencies, T cell activation or memory profiles of MAIT cells, CD1b-restricted GMM-specific and germline-encoded mycolyl-reactive (GEM) cells or CD1d-restricted NKT cells. By contrast, primary BCG vaccination was associated with increased frequencies of γδ T cells as well as a novel subset of CD26⁺CD161⁺TRAV1-2^- IFN-γ-expressing CD4⁺ T cells in infants.

INTERPRETATION

Our findings, that most DURT cell populations were not modulated by BCG, do not preclude a role of BCG in modulating other qualitative aspects of DURT cells. More studies are required to understand the full potential of DURT cells in new TB vaccine strategies.

FUNDING

Aeras, the National Institutes of Health, and the Bill and Melinda Gates Foundation.

Emerging cellular and molecular interactions between the lung microbiota and lung diseases

With the discovery of the lung microbiota, its study in both pulmonary health and disease has become a vibrant area of emerging research interest. Thus far, most studies have described the lung microbiota composition in lung disease quite well, and some of these studies indicated alterations in lung microbial communities related to the onset and development of lung disease and vice versa. However, the underlying mechanisms, particularly the cellular and molecular links, are still largely unknown. In this review, we highlight the current progress in the complex cellular and molecular mechanisms by which the lung microbiome interacts with immune homeostasis and pulmonary disease pathogenesis to advance our understanding of the elaborate function of the lung microbiota in lung disease. We hope that this work can attract more attention to this still-young yet very promising field to facilitate the identification of new therapeutic targets and provide more innovative therapies. Additional accurate standard-based methodologies and technological breakthroughs are critical to propel the field forward to ultimately achieve the goal of maintaining respiratory health.

Tissue-Resident Memory-Like CD8+ T Cells Exhibit Heterogeneous Characteristics in Tuberculous Pleural Effusion

Tissue-resident memory T (TRM) cells are well known to play critical roles in peripheral tissues during virus infection and tumor immunology. Our previous studies indicated that CD69+CD4+ and CD69+CD8+ T cells in tuberculous pleural effusion (TPE) were antigen-specific memory T cells. However, the phenotypical and functional characteristics of CD8+ TRM cells in tuberculosis remain unknown. We found that CD103+CD8+ T cells were the predominant subset of CD103+ lymphocytes in TPE; both CD103 and CD69 expressed on memory CD8+ T cells from TPE were significantly increased compared with those from paired peripheral blood. Phenotypically, CD103+CD69+ and CD103+CD69-CD8+ T cells expressed higher levels of CD45RO than CD103-CD69+CD8+ T cells did; CD103+CD69-CD8+ T cells highly expressed CD27, CD127, and CD62L and some chemokine receptors. We further compared the functional differences among the four distinct CD45RO+CD8+ T subsets identified by CD103 and CD69 expression. In consist with our published results, CD69+CD8+ T cells, but not CD103+CD8+, produced high levels of IFN-γ after treatment with BCG in the presence of BFA. Nevertheless, CD103-CD69+ and CD103+CD69+ memory CD8+ T cells expressed higher levels of Granzyme B, while CD103+CD69- memory CD8+ T cells were characterized as a possibly immunosuppressive subset by highly expressing CTLA-4, CD25, and FoxP3. Furthermore, TGF-β extremely increased CD103 expression but not CD69 in vitro. Together, CD103+CD8+ T cells form the predominant subset of CD103+ lymphocytes in TPE; CD103 and CD69 expression defines distinct CD8+ TRM-like subsets exhibiting phenotypical and functional heterogeneity. Our findings provide an important theoretical basis to optimize and evaluate new tuberculosis vaccines.

Type I Natural Killer T Cells as Key Regulators of the Immune Response to Infectious Diseases

The immune system must work in an orchestrated way to achieve an optimal response upon detection of antigens. The cells comprising the immune response are traditionally divided into two major subsets, innate and adaptive, with particular characteristics for each type. Type I natural killer T (iNKT) cells are defined as innate-like T cells sharing features with both traditional adaptive and innate cells, such as the expression of an invariant T cell receptor (TCR) and several NK receptors. The invariant TCR in iNKT cells interacts with CD1d, a major histocompatibility complex class I (MHC-I)-like molecule. CD1d can bind and present antigens of lipid nature and induce the activation of iNKT cells, leading to the secretion of various cytokines, such as gamma interferon (IFN-γ) and interleukin 4 (IL-4). These cytokines will aid in the activation of other immune cells following stimulation of iNKT cells. Several molecules with the capacity to bind to CD1d have been discovered, including α-galactosylceramide. Likewise, several molecules have been synthesized that are capable of polarizing iNKT cells into different profiles, either pro- or anti-inflammatory. This versatility allows NKT cells to either aid or impair the clearance of pathogens or to even control or increase the symptoms associated with pathogenic infections. Such diverse contributions of NKT cells to infectious diseases are supported by several publications showing either a beneficial or detrimental role of these cells during diseases. In this article, we discuss current data relative to iNKT cells and their features, with an emphasis on their driving role in diseases produced by pathogenic agents in an organ-oriented fashion.

Harnessing Unconventional T Cells for Immunotherapy of Tuberculosis

Even if the incidence of tuberculosis (TB) has been decreasing over the last years, the number of patients with TB is increasing worldwide. The emergence of multidrug-resistant and extensively drug-resistant TB is making control of TB more difficult. Mycobacterium bovis bacillus Calmette–Guérin vaccine fails to prevent pulmonary TB in adults, and there is an urgent need for a vaccine that is also effective in patients with human immunodeficiency virus (HIV) coinfection. Therefore, TB control may benefit on novel therapeutic options beyond antimicrobial treatment. Host-directed immunotherapies could offer therapeutic strategies for patients with drug-resistant TB or with HIV and TB coinfection. In the last years, the use of donor lymphocytes after hematopoietic stem cell transplantation has emerged as a new strategy in the cure of hematologic malignancies in order to induce graft-versus leukemia and graft-versus-infection effects. Moreover, adoptive therapy has proven to be effective in controlling cytomegalovirus and Epstein-Barr virus reactivation in immunocompromised patients with ex vivo expanded viral antigen-specific T cells. Unconventional T cells are a heterogeneous group of T lymphocytes with limited diversity. One of their characteristics is that antigen recognition is not restricted by the classical major histocompatibility complex (MHC). They include CD1 (cluster of differentiation 1)–restricted T cells, MHC-related protein-1–restricted mucosal-associated invariant T (MAIT) cells, MHC class Ib–reactive T cells, and γδ T cells. Because these T cells are genotype-independent, they are also termed “donor unrestricted” T cells. The combined features of low donor diversity and the lack of genetic restriction make these cells suitable candidates for T cell–based immunotherapy of TB.

Immune Networks and Therapeutic Targeting of iNKT Cells in Cancer

One of the primary goals in tumor immunotherapy is to reset the immune system from tolerogenic to immunogenic - a process in which invariant natural killer T (iNKT) cells are implicated. iNKT cells develop in the thymus and perform immunosurveillance against tumor cells peripherally. When optimally stimulated, iNKT cells differentiate and display more efficient immune functions. Some cells survive and act as effector memory cells. We discuss the putative roles of iNKT cells in antitumor immunity, and posit that it may be possible to develop novel therapeutic strategies to treat cancers using iNKT cells. In particular, we highlight the challenge of uniquely energizing iNKT cell-licensed dendritic cells to serve as effective immunoadjuvants for both arms of the immune system, thus coupling immunological networks.

Natural Killer T Cells and Mucosal-Associated Invariant T Cells in Lung Infections

The immune system has been traditionally divided into two arms called innate and adaptive immunity. Typically, innate immunity refers to rapid defense mechanisms that set in motion within minutes to hours following an insult. Conversely, the adaptive immune response emerges after several days and relies on the innate immune response for its initiation and subsequent outcome. However, the recent discovery of immune cells displaying merged properties indicates that this distinction is not mutually exclusive. These populations that span the innate-adaptive border of immunity comprise, among others, CD1d-restricted natural killer T cells and MR1-restricted mucosal-associated invariant T cells. These cells have the unique ability to swiftly activate in response to non-peptidic antigens through their T cell receptor and/or to activating cytokines in order to modulate many aspects of the immune response. Despite they recirculate all through the body via the bloodstream, these cells mainly establish residency at barrier sites including lungs. Here, we discuss the current knowledge into the biology of these cells during lung (viral and bacterial) infections including activation mechanisms and functions. We also discuss future strategies targeting these cell types to optimize immune responses against respiratory pathogens.

New Players in Immunity to Tuberculosis: The Host Microbiome, Lung Epithelium, and Innate Immune Cells

Tuberculosis (TB) is a highly contagious infection and devastating chronic disease, causing 10.4 million new infections and 1.8 million deaths every year globally. Efforts to control and eradicate TB are hampered by the rapid emergence of drug resistance and limited efficacy of the only available vaccine, BCG. Immunological events in the airways and lungs are of major importance in determining whether exposure to Mycobacterium tuberculosis (Mtb) results in successful infection or protective immunity. Several studies have demonstrated that the host microbiota is in constant contact with the immune system, and thus continually directs the nature of immune responses occurring during new infections. However, little is known about its role in the eventual outcome of the mycobacterial infection. In this review, we highlight the changes in microbial composition in the respiratory tract and gut that have been linked to the alteration of immune responses, and to the risk, prevention, and treatment of TB. In addition, we summarize our current understanding of alveolar epithelial cells and the innate immune system, and their interaction with Mtb during early infection. Extensive studies are warranted to fully understand the all-inclusive role of the lung microbiota, its interaction with epithelium and innate immune responses and resulting adaptive immune responses, and in the pathogenesis and/or protection from Mtb infection. Novel interventions aimed at influencing the microbiota, the alveolar immune system and innate immunity will shape future strategies of prevention and treatment for TB.

Mycobacterium tuberculosis Rv3615c is a highly immunodominant antigen and specifically induces potent Th1-type immune responses in tuberculosis pleurisy

T-cell responses have been demonstrated to be essential for preventing Mycobacterium tuberculosis infection. The Th1-cytokines produced by T cells, such as INF-γ, IL-2, and TNF-α, not only limit the invasion of M. tuberculosis but also eliminate the pathogen at the site of infection. Bacillus Calmette-Guérin (BCG) is known to induce Th1-type responses but the protection is inadequate. Identification of immunogenic components, in addition to those expressed in BCG, and induction of a broad spectrum of Th1-type responses provide options for generating sufficient adaptive immunity. Here, we studied human pulmonary T-cell responses induced by the M. tuberculosis-specific antigen Rv3615c, a protein with a similar size and sequence homology to ESAT-6 and CFP-10, which induced dominant CD4⁺ T-cell responses in human tuberculosis (TB) models. We characterized T-cell responses including cytokine profiling, kinetics of activation, expansion, differentiation, TCR usage, and signaling of activation induced by Rv3615c compared with other M. tuberculosis-specific antigens. The expanded CD4⁺ T cells induced by Rv3615c predominately produced Th1, but less Th2 and Th17, cytokines and displayed effector/memory phenotypes (CD45RO⁺CD27^-CD127^-CCR7^-). The magnitude of expansion and cytokine production was comparable to those induced by well-characterized the 6 kDa early secreted antigenic target (ESAT-6), the 10 kDa culture filtrate protein (CFP-10) and BCG. Rv3615c contained multiple epitopes Rv3615c_1-15, Rv3615c_6-20, Rv3615c_66-80, Rv3615c_71-85 and Rv3615c_76-90 that activated CD4⁺ T cells. The Rv3615c-specific CD4⁺ T cells shared biased of T-cell receptor variable region of β chain (TCR Vβ) 1, 2, 4, 5.1, 7.1, 7.2 and/or 22 chains to promote their differentiation and proliferation respectively, by triggering a signaling cascade. Our data suggest that Rv3615c is a major target of Th1-type responses and can be a highly immunodominant antigen specific for M. tuberculosis infection.

Targeting Innate-Like T Cells in Tuberculosis

Peptide-specific conventional T cells have been major targets for designing most antimycobacterial vaccines. Immune responses mediated by conventional T cells exhibit a delayed onset upon primary infection and are highly variable in different human populations. In contrast, innate-like T cells quickly respond to pathogens and display effector functions without undergoing extensive clonal expansion. Specifically, the activation of innate-like T cells depends on the promiscuous interaction of highly conserved antigen-presenting molecules, non-peptidic antigens, and likely semi-invariant T cell receptors. In antimicrobial immune responses, mucosal-associated invariant T cells are activated by riboflavin precursor metabolites presented by major histocompatibility complex-related protein I, while lipid-specific T cells including natural killer T cells are activated by lipid metabolites presented by CD1 proteins. Multiple innate-like T cell subsets have been shown to be protective or responsive in mycobacterial infections. Through rapid cytokine secretion, innate-like T cells function in early defense and memory response, offering novel advantages over conventional T cells in the design of anti-tuberculosis strategies.

Bacillus Calmette-Guérin (BCG) Revaccination of Adults with Latent Mycobacterium tuberculosis Infection Induces Long-Lived BCG-Reactive NK Cell Responses

One third of the global population is estimated to be latently infected with Mycobacterium tuberculosis We performed a phase I randomized controlled trial of isoniazid preventive therapy (IPT) before revaccination with bacillus Calmette-Guérin (BCG) in healthy, tuberculin skin test-positive (≥15-mm induration), HIV-negative South African adults. We hypothesized that preclearance of latent bacilli with IPT modulates BCG immunogenicity following revaccination. Frequencies and coexpression of IFN-γ, TNF-α, IL-2, IL-17, and/or IL-22 in CD4 T cells and IFN-γ-expressing CD8 T, γδ T, CD3(+)CD56(+) NKT-like, and NK cells in response to BCG were measured using whole blood intracellular cytokine staining and flow cytometry. We analyzed 72 participants who were revaccinated with BCG after IPT (n = 33) or without prior IPT (n = 39). IPT had little effect on frequencies or cytokine coexpression patterns of M. tuberculosis- or BCG-specific responses. Revaccination transiently boosted BCG-specific Th1 cytokine-expressing CD4, CD8, and γδ T cells. Despite high frequencies of IFN-γ-expressing BCG-reactive CD3(+)CD56(+) NKT-like cells and CD3(-)CD56(dim) and CD3(-)CD56(hi) NK cells at baseline, BCG revaccination boosted these responses, which remained elevated up to 1 y after revaccination. Such BCG-reactive memory NK cells were induced by BCG vaccination in infants, whereas in vitro IFN-γ expression by NK cells upon BCG stimulation was dependent on IL-12 and IL-18. Our data suggest that isoniazid preclearance of M. tuberculosis bacilli has little effect on the magnitude, persistence, or functional attributes of lymphocyte responses boosted by BCG revaccination. Our study highlights the surprising durability of BCG-boosted memory NKT-like and NK cells expressing antimycobacterial effector molecules, which may be novel targets for tuberculosis vaccines.

Decreased IL-17 during treatment of sputum smear-positive pulmonary tuberculosis due to increased regulatory T cells and IL-10

BACKGROUND

Tuberculosis (TB) remains a major public health concern worldwide. Previous studies have demonstrated that IL-17 plays an important role in initial immune response and is involved in both immune-mediated protection and pathology following infection with Mycobacterium tuberculosis (MTB). However, the alterations and regulation of plasma IL-17 level during TB treatment remain unclear. Moreover, the cell type responsible for the production of IL-17 in TB patients requires further study.

METHODS

A total of 20 acid-fast bacilli smear-positive (AFB-positive) pulmonary TB patients and 20 age- and gender-matched healthy volunteers were included in our study. Blood samples were collected in heparinized tubes at the time of diagnosis (AFB-positive group) and 3 weeks after the initiation of therapy, when the sputum smear conversion (AFB-negative group) occurred, followed by symptomatic improvement. IL-17 levels and IL-17-producing cells in PBMCs were detected. Lymphocyte populations in the peripheral blood between the AFB-positive and AFB-negative groups were compared by flow-cytometry. A549 cells, a cell line of alveolar epithelial cells, were applied to determine the extent of the pathological damage mediated by IL-17 following MTB infection. Recombinant human IL-10 was used to investigate the regulation of IL-17 expression after sputum smear conversion in AFB-positive pulmonary TB patients.

RESULTS

Plasma IL-17 level were elevated in patients with sputum AFB-positive pulmonary TB, but substantially decreased after TB treatment and smear conversion. Our data indicate that NKT-like cells might be the main source of IL-17, in addition to conventional T cells in AFB-positive pulmonary TB patients. The secretion of IL-17 may be suppressed by regulatory T (Treg) cells and IL-10 during TB treatment. Moreover, the IL-17 levels were positively correlated to both the C-reactive protein and erythrocyte sedimentation rate. Therefore, IL-17 was capable of alveolar epithelial cell damage following MTB infection.

CONCLUSION

The increase in the frequency of Treg cells and IL-10 levels was associated with a decrease in IL-17 in patients receiving TB treatment. Thus, IL-10 and Tregs may function to inhibit immune-mediated pathology in TB patients.

The source of Mycobacterium tuberculosis-specific IFN-γ production in peripheral blood mononuclear cells of TB patients

Mycobacterium tuberculosis (Mtb)-specific IFN-γ secretion plays important roles in anti-tuberculosis (TB) immunity. Mtb-specific IFN-γ response can be induced in HIV/TB co-infected patients with a low CD4 lymphocyte count; this suggests that the source of Mtb-specific IFN-γ production is not limited in CD4(+) T lymphocytes. Currently, the major sources of Mtb-specific IFN-γ production and the function and phenotype of Mtb-specific IFN-γ-producing cells still remain unclear. Thirty-nine participants (24 active TB patients, 10 HIV/TB co-infected patients, and 5 healthy volunteers) were recruited according to conventional tests and Mtb-specific IFN-γ ELISPOT assay. Multicolor flow cytometry was used to investigate the production of intracellular IFN-γ in peripheral blood mononuclear cells (PBMCs) after Mtb-specific antigen stimulation. Our results showed that CD4(+), CD8(+) T cells and NK cells are all major sources of Mtb-specific IFN-γ production in PBMCs of TB patients. Moreover, CD8(+) T cells are the highest number of Mtb-specific IFN-γ-producing cells in HIV/TB co-infected patients. Although the activity of NK cells is significantly reduced in TB patients when compared with healthy controls, Mtb-specific antigen stimulation induces a significant increase in NK cell activity. We also showed that CD45RO is the characteristic marker of Mtb-specific IFN-γ-producing T cells but not that of Mtb-specific IFN-γ-producing NK cells in peripheral blood. High expression of CD11a may be the characteristic feature of Mtb-specific IFN-γ-producing NK cells. This study put forward a new insight on the source of antigen-specific IFN-γ-production in PBMCs of TB patients.