Increased susceptibility of mice lacking T-bet to infection with Mycobacterium tuberculosis correlates with increased IL-10 and decreased IFN-gamma production

Therapeutic Modulation of Arginase with nor-NOHA Alters Immune Responses in Experimental Mouse Models of Pulmonary Tuberculosis including in the Setting of Human Immunodeficiency Virus (HIV) Co-Infection

L-arginine metabolism is strongly linked with immunity to mycobacteria, primarily through the antimicrobial activity of nitric oxide (NO). The potential to modulate tuberculosis (TB) outcomes through interventions that target L-arginine pathways are limited by an incomplete understanding of mechanisms and inadequate in vivo modeling. These gaps in knowledge are compounded for HIV and Mtb co-infections, where activation of arginase-1 due to HIV infection may promote survival and replication of both Mtb and HIV. We utilized in vitro and in vivo systems to determine how arginase inhibition using Nω-hydroxy-nor-L-arginine (nor-NOHA) alters L-arginine pathway metabolism relative to immune responses and disease outcomes following Mtb infection. Treatment with nor-NOHA polarized murine macrophages (RAW 264.7) towards M1 phenotype, increased NO, and reduced Mtb in RAW macrophages. In Balb/c mice, nor-NOHA reduced pulmonary arginase and increased the antimicrobial metabolite spermine in association with a trend towards reduced Mtb CFU in lung. In humanized immune system (HIS) mice, HIV infection increased plasma arginase and heightened the pulmonary arginase response to Mtb. Treatment with nor-NOHA increased cytokine responses to Mtb and Mtb/HIV in lung tissue but did not significantly alter bacterial burden or viral load. Our results suggest that L-arginine pathway modulators may have potential as host-directed therapies to augment antibiotics in TB chemotherapy.

Inborn errors of human transcription factors governing IFN-γ antimycobacterial immunity

Inborn errors of immunity (IEI) delineate redundant and essential defense mechanisms in humans. We review 15 autosomal-dominant (AD) or -recessive (AR) IEI involving 11 transcription factors (TFs) and impairing interferon-gamma (IFN-γ) immunity, conferring a predisposition to mycobacterial diseases. We consider three mechanism-based categories: 1) IEI mainly affecting myeloid compartment development (AD GATA2 and AR and AD IRF8 deficiencies), 2) IEI mainly affecting lymphoid compartment development (AR FOXN1, AR PAX1, AR RORγ/RORγT, AR T-bet, AR c-Rel, AD STAT3 gain-of-function (GOF), and loss-of-function (LOF) deficiencies), and 3) IEI mainly affecting myeloid and/or lymphoid function (AR and AD STAT1 LOF, AD STAT1 GOF, AR IRF1, and AD NFKB1 deficiencies). We discuss the contribution of the discovery and study of inborn errors of TFs essential for host defense against mycobacteria to molecular and cellular analyses of human IFN-γ immunity.

Early T-bet promotes LFA1 upregulation required for CD8+ effector and memory T cell development

The T-box transcription factor T-bet is regarded as a "master regulator" of CD4+ Th1 differentiation and IFN-γ production. However, in multiple models of infection, T-bet appears less critical for CD8+ T cell expansion and effector function. Here, we show that following vaccination with a replication-deficient strain of Toxoplasma gondii, CD8+ T cell expression of T-bet is required for optimal expansion of parasite-specific effector CD8+ T cells. Analysis of the early events associated with T cell activation reveals that the α chain of LFA1, CD11a, is a target of T-bet, and T-bet is necessary for CD8+ T cell upregulation of this integrin, which influences the initial priming of CD8+ effector T cells. We propose that the early expression of T-bet represents a T cell-intrinsic factor that optimizes T-DC interactions necessary to generate effector responses.

Mouse Models for Mycobacterium tuberculosis Pathogenesis: Show and Do Not Tell

Science has been taking profit from animal models since the first translational experiments back in ancient Greece. From there, and across all history, several remarkable findings have been obtained using animal models. One of the most popular models, especially for research in infectious diseases, is the mouse. Regarding research in tuberculosis, the mouse has provided useful information about host and bacterial traits related to susceptibility to the infection. The effect of aging, sexual dimorphisms, the route of infection, genetic differences between mice lineages and unbalanced immunity scenarios upon Mycobacterium tuberculosis infection and tuberculosis development has helped, helps and will help biomedical researchers in the design of new tools for diagnosis, treatment and prevention of tuberculosis, despite various discrepancies and the lack of deep study in some areas of these traits.

Mendelian Susceptibility to Mycobacterial Diseases (MSMD) in a 13-Year-Old Ethiopian Girl with Autosomal Dominant Interferon Gamma Receptor 1(IFN-γ R1) Defect: A Clinical Diagnostic and Treatment Challenge

Background

Mendelian susceptibility to mycobacterial diseases (MSMD) is an inborn error of immunity categorized as defects in intrinsic and innate immunity. MSMD is characterized by vulnerability to less virulent mycobacteria, such as Bacillus Calmette-Guérin (BCG) vaccine strains, as well as environmental mycobacteria (EM). The definitive diagnosis is made by genetic analysis. Treatments constitute antimycobacterial, interferon-gamma, surgery, and hematopoietic stem cell transplantation (HSCT), which is the only known curative treatment. The mortality rate ranges from 40% to 80% depending on the severity of the mutation.

Case

A 13-year-old female patient had multiple hospital visits since the age of 6 months. The most striking diagnosis was repeated mycobacterial infections. She had tuberculosis affecting lymph nodes, skin and soft tissue, bone and joints, the lungs, and epidural and paraspinal regions. She has taken all the childhood vaccines, including BCG. She has been treated four times with first-line and once with second-line antituberculosis drugs. Currently, she is on treatment for nontuberculous mycobacteria and is receiving interferon-gamma. Genetic studies showed autosomal dominant Mendelian susceptibility to mycobacterial disease due to IFNG-R1 defect.

Conclusion

To the authors' knowledge, this is the first case report of Mendelian susceptibility to mycobacterial diseases secondary to interferon gamma receptor 1(IFNG-R1) defect in Ethiopia. Although it has been immensely challenging, our multidisciplinary team has learned a lot from the clinical presentation, diagnosis, and management of this child.

Unique Reciprocal Association Seen Between Latent Tuberculosis Infection and Diabetes Is Due to Immunoendocrine Modulation (DM-LTB-1)

Aim

The prevalence of latent tuberculosis infection (LTBI) among diabetes patients is poorly studied. In the present study, the prevalence of LTBI among pre-diabetes and diabetes patients was studied, along with immunoendocrine biomarkers (n = 804).

Methods

LTBI was screened by Quantiferon TB gold in Normal glucose tolerance [(NGT); n = 170, [Pre-diabetes (PDM; n = 209), Newly diagnosed diabetes (NDM; n = 165) and Known diabetes (KDM; n = 260) subjects. CRP, TNF-α, IL-6, IL-1β, IFN-β, IL-12, IFN-γ, IL-2, insulin, leptin, and adiponectin levels in serum and IFN-γ levels in quantiferon supernatants were quantified by ELISA. The expression of T-bet was quantified using qRT-PCR. Serum TBARS and nitrite levels were quantified by colorimetry.

Results

The LTBI prevalence was 32% in NGT, 23% in PDM, 24% in NDM, and 32% in KDM groups, with an adjusted OR of 0.61 (p < 0.05). Downregulation of CRP, TNF-α, and nitrites and upregulation of adiponectin could be responsible for LTBI mediated protection against insulin resistance (IR), while the high levels of IL-1β, IL-12, and leptin could be responsible for IR mediated anti-TB immunity. The defective antigen-specific IFN-γ response, as seen in the KDM group, could be responsible for the low detection rate of LTBI and high probability of endogenous reactivation.

Conclusion

There appears to be a biphasic relationship between diabetes-latent tuberculosis: At the early stages of diabetes it is reciprocal, while at a late stage it is synergistic, this important phenomenon obviously needs further research.

T cell transcription factor expression evolves over time in granulomas from Mycobacterium tuberculosis-infected cynomolgus macaques

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is a global health concern, yearly resulting in 10 million new cases of active TB. Immunologic investigation of lung granulomas is essential for understanding host control of bacterial replication. Here, we identify and compare the pathological, cellular, and functional differences in granulomas at 4, 12, and 20 weeks post-infection in Chinese cynomolgus macaques. Original granulomas differ in transcription-factor expression within adaptive lymphocytes, with those at 12 weeks showing higher frequencies of CD8⁺T-bet⁺ T cells, while CD4⁺T-bet⁺ T cells increase at 20 weeks post-infection. The appearance of T-bet⁺ adaptive T cells at 12 and 20 weeks is coincident with a reduction in bacterial burden, suggesting their critical role in Mtb control. This study highlights the evolution of T cell responses within lung granulomas, suggesting that vaccines promoting the development and migration of T-bet⁺ T cells would enhance mycobacterial control.

Grant et al. investigate the pathological, cellular, and functional differences in TB lung granulomas from macaques. The data reveal that most T cells at early time points have low frequencies of transcription factor expression, while T cells at later time points have increased expression of T-bet and a reduction in bacterial burden.

Th1 cells are dispensable for primary clearance of Chlamydia from the female reproductive tract of mice

Protective immune responses to Chlamydia infection within the female reproductive tract (FRT) are incompletely understood. MHC class II-restricted CD4 Th1 responses are believed to be vital for bacterial clearance due to their capacity to secrete IFN-γ, but an essential requirement for T-bet-expressing Th1 cells has yet to be demonstrated in the mouse model of Chlamydia infection. Here, we investigated the role of T-bet and IFN-γ in primary clearance of Chlamydia after FRT infection. Surprisingly, IFN-γ producing CD4 T cells from the FRT expressed low levels of T-bet throughout infection, suggesting that classical T-bet-expressing Th1 cells are inefficiently generated and therefore unlikely to participate in bacteria clearance. Furthermore, mice deficient in T-bet expression or with a CD4-specific T-bet deficiency cleared FRT infection similarly to wild-type controls. T-bet-deficient mice displayed significant skewing of FRT CD4 T cells towards Th17 responses, demonstrating that compensatory effector pathways are generated in the absence of Th1 cells. In marked contrast, IFN-γ-, and IFN-γR-deficient mice were able to reduce FRT bacterial burdens, but suffered systemic bacterial dissemination and 100% mortality. Together, these data demonstrate that IFN-γ signaling is essential to protect mice from fatal systemic disease, but that classical T-bet-expressing Th1 cells are non-essential for primary clearance within the FRT. Exploring the protective contribution of Th1 cells versus other CD4 effector lineages could provide important information for the generation of new Chlamydia vaccines.

The production of IFN-γ by CD4 Th1 cells is thought to be critical for the clearance of Chlamydia from the female reproductive tract (FRT), but this has not been formally tested. Here we demonstrate that T-bet+ Th1 cells are not essential for effective Chlamydia clearance. Furthermore, the impact of IFN-γ deficiency or depletion is largely observed as a failure to control bacterial dissemination, rather than clearance from the FRT. Together, these data suggest that different immunological mechanisms are responsible for restraining systemic spread of bacteria versus FRT control. Defining alternative non-Th1 CD4 effector mechanisms that are responsible for controlling Chlamydia replication within the FRT could be foundational for future vaccine development.

Expression Regulation and Function of T-Bet in NK Cells

Natural killer (NK) cells are cytotoxic innate lymphocytes that play an important role in immune surveillance. The development, maturation and effector functions of NK cells are orchestrated by the T-box transcription factor T-bet, whose expression is induced by cytokines such as IFN-γ, IL-12, IL-15 and IL-21 through the respective cytokine receptors and downstream JAK/STATs or PI3K-AKT-mTORC1 signaling pathways. In this review, we aim to discuss the expression and regulation of T-bet in NK cells, the role of T-bet in mouse NK cell development, maturation, and function, as well as the role of T-bet in acute, chronic infection, inflammation, autoimmune diseases and tumors.

Transcriptomic Profiles in Children With Septic Shock With or Without Immunoparalysis

Background

Severe innate immune suppression, termed immunoparalysis, is associated with increased risks of nosocomial infection and mortality in children with septic shock. Currently, immunoparalysis cannot be clinically diagnosed in children, and mechanisms remain unclear. Transcriptomic studies identify subsets of septic children with downregulation of genes within adaptive immune pathways, but assays of immune function have not been performed as part of these studies, and little is known about transcriptomic profiles of children with immunoparalysis.

Methods

We performed a nested case-control study to identify differences in RNA expression patterns between children with septic shock with immunoparalysis (defined as lipopolysaccharide (LPS)-induced tumor necrosis factor (TNF)α response < 200 pg/ml) vs those with normal LPS-induced TNFα response. Children were enrolled within 48 hours of the onset of septic shock and divided into two groups based on LPS-induced TNFα response. RNA was extracted from whole blood for RNAseq, differential expression analyses using DESeq2 software, and pathway analyses using Ingenuity Pathway Analysis.

Results

32 children were included in analyses. Comparing those with immunoparalysis (n =19) to those with normal TNFα response (n = 13), 2,303 transcripts were differentially expressed with absolute value fold change ≥ 1.5 and false discovery rate ≤ 0.05. The majority of downregulated pathways in children with immunoparalysis were pathways that involved interactions between innate and adaptive immune cells necessary for cell-mediated immunity, crosstalk between dendritic cells and natural killer cells, and natural killer cell signaling pathways. Upregulated pathways included those involved in humoral immunity (T helper cell type 2), corticotropin signaling, platelet activation (GP6 signaling), and leukocyte migration and extravasation.

Conclusions

Our study suggests that gene expression data might be useful to identify children with immunoparalysis and identifies several key differentially regulated pathways involved in both innate and adaptive immunity. Our ongoing work in this area aims to dissect interactions between innate and adaptive immunity in septic children and to more fully elucidate patient-specific immunologic pathophysiology to guide individualized immunotherapeutic targets.

Metabolic Regulation of Immune Responses to Mycobacterium tuberculosis: A Spotlight on L-Arginine and L-Tryptophan Metabolism

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is a leading cause of death worldwide. Despite decades of research, there is still much to be uncovered regarding the immune response to Mtb infection. Here, we summarize the current knowledge on anti-Mtb immunity, with a spotlight on immune cell amino acid metabolism. Specifically, we discuss L-arginine and L-tryptophan, focusing on their requirements, regulatory roles, and potential use as adjunctive therapy in TB patients. By continuing to uncover the immune cell contribution during Mtb infection and how amino acid utilization regulates their functions, it is anticipated that novel host-directed therapies may be developed and/or refined, helping to eradicate TB.

T-bet-dependent ILC1- and NK cell-derived IFN-γ mediates cDC1-dependent host resistance against Toxoplasma gondii

Host resistance against intracellular pathogens requires a rapid IFN-γ mediated immune response. We reveal that T-bet-dependent production of IFN-γ is essential for the maintenance of inflammatory DCs at the site of infection with a common protozoan parasite, Toxoplasma gondii. A detailed analysis of the cellular sources for T-bet-dependent IFN-γ identified that ILC1s and to a lesser degree NK, but not TH1 cells, were involved in the regulation of inflammatory DCs via IFN-γ. Mechanistically, we established that T-bet dependent innate IFN-γ is critical for the induction of IRF8, an essential transcription factor for cDC1s. Failure to upregulate IRF8 in DCs resulted in acute susceptibility to T. gondii infection. Our data identifies that T-bet dependent production of IFN-γ by ILC1 and NK cells is indispensable for host resistance against intracellular infection via maintaining IRF8+ inflammatory DCs at the site of infection.

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.

T-Bet Controls Susceptibility of Mice to Coxiella burnetii Infection

T-bet is a transcription factor known to initiate and coordinate the gene expression program during Th1 differentiation, which is crucial for clearance of intracellular pathogens. Q fever is a worldwide zoonosis caused by Coxiella burnetii. This bacterium is transmitted to humans by aerosol. Indeed, the inhibition of the Coxiella-specific adaptive Th1 immune response leads to persistent infection and organ injury. How deficiency of T-bet affects host infection by C. burnetii has not been investigated. Here, using mice with a deletion of the T-bet gene and an airborne mode of infection to reproduce the natural conditions of C. burnetii infection, we show that infected T-bet^–/– mice were more affected than wild-type mice. The lack of T-bet leads to defective bacterial control, intense replication, persistent infection, and organ injury manifesting as an increased number of granulomas. The absence of T-bet was also associated with an impaired immune response. Indeed, the production of the immunomodulatory cytokines interleukin (IL)-6 and IL-10 was increased, whereas the expression of microbicidal genes by splenocytes was impaired. Moreover, the absence of T-bet exhibited impaired production of interferon-γ, the principal cytokine released by Th1 effector cells. Thus, our study highlights the key role of T-bet in the control of C. burnetii infection in mice and leads to a reappraisal of granulomas in the pathogenesis of Q fever disease.

M1 Macrophage Derived Exosomes Aggravate Experimental Autoimmune Neuritis via Modulating Th1 Response

Guillain–Barré syndrome (GBS), an immune-mediated disorder affecting the peripheral nervous system, is the most common and severe acute paralytic neuropathy. GBS remains to be potentially life-threatening and disabling despite the increasing availability of current standard therapeutic regimens. Therefore, more targeted therapeutics are in urgent need. Macrophages have been implicated in both initiation and resolution of experimental autoimmune neuritis (EAN), the animal model of GBS, but the exact mechanisms remain to be elucidated. It has been increasingly appreciated that exosomes, a type of extracellular vesicles (EVs), are of importance for functions of macrophages. Nevertheless, the roles of macrophage derived exosomes in EAN/GBS remain unclear. Here we determined the effects of macrophage derived exosomes on the development of EAN in Lewis rats. M1 macrophage derived exosomes (M1 exosomes) were found to aggravate EAN via boosting Th1 and Th17 response, while M2 macrophage derived exosomes (M2 exosomes) showed potentials to mitigate disease severity via a mechanism bypassing Th1 and Th17 response. Besides, both M1 and M2 exosomes increased germinal center reactions in EAN. Further in vitro studies confirmed that M1 exosomes could directly promote IFN-γ production in T cells and M2 exosomes were not capable of inhibiting IFN-γ expression. Thus, our data identify a previously undescribed means that M1 macrophages amplify Th1 response via exosomes and provide novel insights into the crosstalk between macrophages and T cells as well.

The evolving role of T-bet in resistance to infection

The identification of T-bet as a key transcription factor associated with the development of IFNγ-producing CD4⁺ T cells predicted a crucial role for T-bet in cell-mediated immunity and in resistance to many intracellular infections. This idea was reinforced by initial reports showing that T-bet-deficient mice were more susceptible to pathogens that survived within the lysosomal system of macrophages. However, subsequent studies revealed IFNγ-dependent, T-bet-independent pathways of resistance to diverse classes of microorganisms that occupy other intracellular niches. Consequently, a more complex picture has emerged of how T-bet and the related transcription factor eomesodermin (EOMES) coordinate many facets of the immune response to bona fide pathogens as well as commensals. This article provides an overview of the discovery and evolutionary relationship between T-bet and EOMES and highlights the studies that have uncovered broader functions of T-bet in innate and adaptive immunity and in the development of the effector and memory T cell populations that mediate long-term resistance to infection.

Major Histocompatibility Complex Class II-Restricted, CD4+ T Cell-Dependent and -Independent Mechanisms Are Required for Vaccine-Induced Protective Immunity against Coxiella burnetii

To understand the role of major histocompatibility complex class I (MHC-I) and MHC-II in vaccine-mediated protection against Coxiella burnetii, we evaluated the protective efficacy of a formalin-inactivated C. burnetii Nine Mile phase I vaccine (PIV) in β2-microglobulin-deficient (B2m KO) and MHC-II-deficient (MHC-II KO) mice. Vaccination reduced disease severity in wild-type (WT) and B2m KO mice but failed to reduce bacterial burden in MHC-II KO mice. This suggests that the MHC-II antigen presentation pathway is required for PIV-mediated protection against C. burnetii infection. MHC-I and MHC-II affect antibody isotype switching, since both PIV-vaccinated B2m KO and MHC-II KO mice produced less Coxiella-specific IgG than PIV-vaccinated WT mice. Interestingly, MHC-II and CD4 deficiencies were not equivalent in terms of splenomegaly and bacterial clearance. This demonstrates a partial role for CD4+ T cells while revealing MHC-II-restricted, CD4-independent mechanisms. Adoptive transfer of CD4+ T cells from PIV-vaccinated WT mice to naive CD4-deficient (CD4 KO) mice demonstrated that antigen-experienced CD4+ T cells are sufficient to generate protection. Conversely, transfer of naive CD4+ T cells to PIV-vaccinated CD4 KO mice exacerbates disease. Using Tbet-deficient (Tbet KO) mice, we showed a partial role for Th1 subset CD4+ T cells in vaccine protection. Furthermore, Th1-independent roles for Tbet were suggested by significant differences in disease between PIV-vaccinated Tbet KO and CD4 KO mice. Interferon gamma was shown to contribute to the host inflammatory response but not bacterial clearance. Collectively, these findings suggest that vaccine-induced protective immunity against a murine model of experimental Q fever requires MHC-II-restricted, CD4+ T cell-dependent and -independent mechanisms that can be exploited for a new-generation human Q fever vaccine.

Characterization of immune response against Mycobacterium marinum infection in the main hematopoietic organ of adult zebrafish (Danio rerio)

Tuberculosis remains a major global health challenge. To gain information about genes important for defense against tuberculosis, we used a well-established tuberculosis model; Mycobacterium marinum infection in adult zebrafish. To characterize the immunological response to mycobacterial infection at 14 days post infection, we performed a whole-genome level transcriptome analysis using cells from kidney, the main hematopoietic organ of adult zebrafish. Among the upregulated genes, those associated with immune signaling and regulation formed the largest category, whereas the largest group of downregulated genes had a metabolic role. We also performed a forward genetic screen in adult zebrafish and identified a fish line with severely impaired survival during chronic mycobacterial infection. Based on transcriptome analysis, these fish have decreased expression of several immunological genes. Taken together, these results give new information about the genes involved in the defense against mycobacterial infection in zebrafish.

Urban Air Pollution Particulates Suppress Human T-Cell Responses to Mycobacterium Tuberculosis

Tuberculosis (TB) and air pollution both contribute significantly to the global burden of disease. Epidemiological studies show that exposure to household and urban air pollution increase the risk of new infections with Mycobacterium tuberculosis (M.tb) and the development of TB in persons infected with M.tb and alter treatment outcomes. There is increasing evidence that particulate matter (PM) exposure weakens protective antimycobacterial host immunity. Mechanisms by which exposure to urban PM may adversely affect M.tb-specific human T cell functions have not been studied. We, therefore, explored the effects of urban air pollution PM_2.5 (aerodynamic diameters ≤2.5µm) on M.tb-specific T cell functions in human peripheral blood mononuclear cells (PBMC). PM_2.5 exposure decreased the capacity of PBMC to control the growth of M.tb and the M.tb-induced expression of CD69, an early surface activation marker expressed on CD3⁺ T cells. PM_2.5 exposure also decreased the production of IFN-γ in CD3⁺, TNF-α in CD3⁺ and CD14⁺ M.tb-infected PBMC, and the M.tb-induced expression of T-box transcription factor TBX21 (T-bet). In contrast, PM_2.5 exposure increased the expression of anti-inflammatory cytokine IL-10 in CD3⁺ and CD14⁺ PBMC. Taken together, PM_2.5 exposure of PBMC prior to infection with M.tb impairs critical antimycobacterial T cell immune functions.

T-bet optimizes CD4 T-cell responses against influenza through CXCR3-dependent lung trafficking but not functional programming

Although clearance of many intracellular pathogens requires T-bet-dependent CD4 T cell programming, the extent to which T-bet is needed to direct protective CD4 responses against influenza is not known. Here, we characterize wild-type and T-bet-deficient CD4 cells during murine influenza infection. Surprisingly, although T-bet expression has broad impacts on cytokine production by virus-specific CD4 cells, the protective efficacy of T-bet-deficient effector cells is only marginally reduced. This reduction is due to lower CXCR3 expression, leading to suboptimal accumulation of activated T-bet-deficient cells in the infected lung. However, T-bet-deficient cells outcompete wild-type cells to form lung-resident and circulating memory populations following viral clearance, and primed T-bet-deficient mice efficiently clear supralethal heterosubtypic influenza challenges even when depleted of CD8 T cells. These results are relevant to the identification of more incisive correlates of protective T cells and for vaccines that aim to induce durable cellular immunity against influenza.

Cyclooxygenase inhibitors impair CD4 T cell immunity and exacerbate Mycobacterium tuberculosis infection in aerosol-challenged mice

Tuberculosis, caused by infection with Mycobacterium tuberculosis (Mtb), kills over 1.6 million people each year despite availability of antibiotics. The increase in drug resistant Mtb strains is a major public health emergency and host-directed therapy as adjunct to antibiotic treatment has gained increased interest. Cyclooxygenase inhibitors (COXi) are frequently used drugs to alleviate tuberculosis related symptoms. Mouse studies of acute intravenous Mtb infection have suggested a potential benefit of COXi for host-directed therapy. Here we show that COXi treatment (ibuprofen and celecoxib) is detrimental to Mtb control in different mouse models of respiratory infection. This effect links to impairments of the Type-1 helper (Th1) T-cell response as CD4 T-cells in COXi-treated animals have significantly decreased Th1 differentiation, reduced IFNγ expression and decreased protective capacity upon adoptive transfer. If confirmed in clinical trials, these findings could have major impact on global health and question the use of COXi for host-directed therapy.

A Case for Antibodies as Mechanistic Correlates of Immunity in Tuberculosis

Tuberculosis infects one quarter of the world's population and is the leading cause of death by a single infectious agent, responsible for a reported 1.3 million deaths in 2017. While Mycobacterium tuberculosis is treatable with antibiotic therapy, the increased prevalence of drug resistance, coupled with the variable efficacy of the only widely approved vaccine, has highlighted the need for creative approaches to therapeutic and vaccine development. Historically, a productive immune response to M. tuberculosis has been thought to be nearly entirely cell-mediated, with humoral immunity being largely dismissed. However, in this review, we will discuss the historical skepticism surrounding the role of the humoral immune response to M. tuberculosis, and examine more recent evidence suggesting that antibodies may play a valuable role in host defense against the pathogen. Despite the amount of data portraying antibodies in a negative light, emerging data have begun to highlight the unexpected role of antibodies in M. tuberculosis control. Specifically, it has become clear that antibody features of both the variable and constant domain (Fc) ultimately determine the extent to which antibodies modulate disease. Thus, a more precise definition of the antigen-binding and innate immune recruiting functions of antibodies that contribute to M. tuberculosis restriction, are sure to help guide the development of next-generation therapeutics and vaccines to curb this global epidemic.

Loss of T-bet confers survival advantage to influenza-bacterial superinfection

The transcription factor, T-bet, regulates type 1 inflammatory responses against a range of infections. Here, we demonstrate a previously unaddressed role of T-bet, to influenza virus and bacterial superinfection. Interestingly, we found that T-bet deficiency did not adversely affect the efficacy of viral clearance or recovery compared to wild-type hosts. Instead, increased infiltration of neutrophils and production of Th17 cytokines (IL-17 and IL-22), in lungs of influenza virus-infected T-bet-/- mice, were correlated with survival advantage against subsequent infection by Streptococcus pneumoniae Neutralization of IL-17, but not IL-22, in T-bet-/- mice increased pulmonary bacterial load, concomitant with decreased neutrophil infiltration and reduced survival of T-bet-/- mice. IL-17 production by CD8+, CD4+ and γδ T cell types was identified to contribute to this protection against bacterial superinfection. We further showed that neutrophil depletion in T-bet-/- lungs increased pulmonary bacterial burden. These results thus indicate that despite the loss of T-bet, immune defences required for influenza viral clearance are fully functional, which in turn enhances protective type 17 immune responses against lethal bacterial superinfections.

Enhanced protection conferred by mucosal BCG vaccination associates with presence of antigen-specific lung tissue-resident PD-1+ KLRG1- CD4+ T cells

BCG, the only vaccine licensed against tuberculosis, demonstrates variable efficacy in humans. Recent preclinical studies highlight the potential for mucosal BCG vaccination to improve protection. Lung tissue-resident memory T cells reside within the parenchyma, potentially playing an important role in protective immunity to tuberculosis. We hypothesised that mucosal BCG vaccination may enhance generation of lung tissue-resident T cells, affording improved protection against Mycobacterium tuberculosis. In a mouse model, mucosal intranasal (IN) BCG vaccination conferred superior protection in the lungs compared to the systemic intradermal (ID) route. Intravascular staining allowed discrimination of lung tissue-resident CD4⁺ T cells from those in the lung vasculature, revealing that mucosal vaccination resulted in an increased frequency of antigen-specific tissue-resident CD4⁺ T cells compared to systemic vaccination. Tissue-resident CD4⁺ T cells induced by mucosal BCG displayed enhanced proliferative capacity compared to lung vascular and splenic CD4⁺ T cells. Only mucosal BCG induced antigen-specific tissue-resident T cells expressing a PD-1⁺ KLRG1^- cell-surface phenotype. These cells constitute a BCG-induced population which may be responsible for the enhanced protection observed with IN vaccination. We demonstrate that mucosal BCG vaccination significantly improves protection over systemic BCG and this correlates with a novel population of BCG-induced lung tissue-resident CD4⁺ T cells.

ID2 and ID3 are indispensable for Th1 cell differentiation during influenza virus infection in mice

Antigen-specific Th1 cells could be a passage to the infection sites during infection to execute effector functions, such as help CD8⁺ T cells to localize in these sites by secretion of anti-viral cytokines-IFN-γ or direct cytotoxicity of antigen-bearing cells. However, the molecular components that modulate Th1 cell differentiation and function in response to viral infection remain incompletely understood. Here, we reported that both inhibitor of DNA binding 3(Id3) protein and inhibitor of DNA binding 2(Id2) protein promoted Th1 cell differentiation. Depletion of Id3 or Id2 led to severe defect of Th1 cell differentiation during influenza virus infection. Whereas depletion of both Id3 and Id2 in CD4⁺ T cells restrained Th1 cell differentiation to a greater extent, indicating that Id3 and Id2 nonredundantly regulate Th1 cell differentiation. Moreover, deletion of E-proteins, the antagonists of Id proteins, greatly enhanced Th1 cell differentiation. Mechanistic study indicated that E-proteins suppressed Th1 cell differentiation by directly binding to the regulatory elements of Th1 cell master regulator T-bet and regulate T-bet expression. Thus, our findings identified Id-protein's importance for Th1 cells and clarified the nonredundant role of Id3 and Id2 in regulating Th1 cell differentiation, providing novel insight that Id3-Id2-E protein axis are essential for Th1 cell polarization.

Suppression of Th1 Priming by TLR2 Agonists during Cutaneous Immunization Is Mediated by Recruited CCR2+ Monocytes

Effective subunit vaccines require the incorporation of adjuvants that stimulate cells of the innate immune system to generate protective adaptive immune responses. Pattern recognition receptor agonists are a growing class of potential adjuvants that can shape the character of the immune response to subunit vaccines by directing the polarization of CD4 T cell differentiation to various functional subsets. In the current study, we applied a high-throughput in vitro screen to assess murine CD4 T cell polarization by a panel of pattern recognition receptor agonists. This identified lipopeptides with TLR2 agonist activity as exceptional Th1-polarizing adjuvants. In vivo, we demonstrated that i.v. administration of TLR2 agonists with Ag in mice replicated the findings from in vitro screening by promoting strong Th1 polarization. In contrast, TLR2 agonists inhibited priming of Th1 responses when administered cutaneously in mice. This route-specific suppression was associated with infiltrating CCR2⁺ cells in the skin-draining lymph nodes and was not uniquely dependent on any of the well characterized subsets of dendritic cells known to reside in the skin. We further demonstrated that priming of CD4 T cells to generate Th1 effectors following immunization with the Mycobacterium bovis bacillus Calmette-Guérin (BCG) strain, a lipoprotein-rich bacterium recognized by TLR2, was dependent on the immunization route, with significantly greater Th1 responses with i.v. compared with intradermal administration of BCG. A more complete understanding of route-dependent TLR2 responses may be critical for informed design of novel subunit vaccines and for improvement of BCG and other vaccines based on live-attenuated organisms.

T-bet-independent Th1 response induces intestinal immunopathology during Toxoplasma gondii infection

Coordinated production of IFN-γ by innate and adaptive immune cells is central for host defense, but can also trigger immunopathology. The investigation of the lymphoid cell-specific contribution to the IFN-γ-mediated intestinal pathology during Toxoplasma gondii infection identified CD4+ T cells as a key cell population responsible for IFN-γ-dependent intestinal inflammation and Paneth cell loss, where T-bet-dependent group 1 innate lymphoid cells have a minor role in driving the parasite-induced immunopathology. This was evident from the analysis of T-bet deficiency that did not prevent the intestinal inflammation and instead revealed that T-bet-deficient CD4+ Th1 cells are sufficient for T. gondii-triggered acute ileitis and Paneth cell loss. These results revealed that T-bet-independent Th1 effector cells are major functional mediators of the type I immunopathological response during acute gastrointestinal infection.

Defective positioning in granulomas but not lung-homing limits CD4 T-cell interactions with Mycobacterium tuberculosis-infected macrophages in rhesus macaques

Protection against Mycobacterium tuberculosis (Mtb) infection requires CD4 T cells to migrate into the lung and interact with infected macrophages. In mice, less-differentiated CXCR3⁺ CD4 T cells migrate into the lung and suppress growth of Mtb, whereas CX3CR1⁺ terminally differentiated Th1 cells accumulate in the blood vasculature and do not control pulmonary infection. Here we examine CD4 T-cell differentiation and lung homing during primary Mtb infection of rhesus macaques. Mtb-specific CD4 T cells simultaneously appeared in the airways and blood ∼21-28 days post exposure, indicating that recently primed effectors are quickly recruited into the lungs after entering circulation. Mtb-specific CD4 T cells in granulomas display a tissue-parenchymal CXCR3⁺CX3CR1^-PD-1^hiCTLA-4⁺ phenotype. However, most granuloma CD4 T cells are found within the outer lymphocyte cuff and few localize to the myeloid cell core containing the bacilli. Using the intravascular stain approach, we find essentially all Mtb-specific CD4 T cells in granulomas have extravasated across the vascular endothelium into the parenchyma. Therefore, it is unlikely to be that lung-homing defects introduced by terminal differentiation limit the migration of CD4 T cells into granulomas following primary Mtb infection of macaques. However, intralesional positioning defects within the granuloma may pose a major barrier to T-cell-mediated immunity during tuberculosis.

T-bet and Eomes govern differentiation and function of mouse and human NK cells and ILC1

T-bet and Eomes are T-box transcription factors that drive the differentiation and function of cytotoxic lymphocytes such as NK cells. Their DNA-binding domains are highly similar, suggesting redundant transcriptional activity. However, while these transcription factors have different patterns of expression, the phenotype of loss-of-function mouse models suggests that they play distinct roles in the development of NK cells and other innate lymphoid cells (ILCs). Recent technological advances using reporter mice and conditional knockouts were fundamental in defining the regulation and function of these factors at steady state and during pathological conditions such as various types of cancer or infection. Here, we review these recent developments, focusing on NK cells as prototypical cytotoxic lymphocytes and their development, and also discuss parallels between NK cells and T cells. We also examine the role of T-bet and Eomes in human NK cells and ILC1s. Considering divergent findings on mouse and human ILC1s, we propose that NK cells are defined by coexpression of T-bet and Eomes, while ILC1s express only one of these factors, either T-bet or Eomes, depending on the tissue or the species.

Th1 Differentiation Drives the Accumulation of Intravascular, Non-protective CD4 T Cells during Tuberculosis

Recent data indicate that the differentiation state of Th1 cells determines their protective capacity against tuberculosis. Therefore, we examined the role of Th1-polarizing factors in the generation of protective and non-protective subsets of Mtb-specific Th1 cells. We find that IL-12/23p40 promotes Th1 cell expansion and maturation beyond the CD73⁺CXCR3⁺T-bet^dim stage, and T-bet prevents deviation of Th1 cells into Th17 cells. Nevertheless, IL- 12/23p40 and T-bet are also essential for the production of a prominent subset of intravascular CX3CR1⁺KLRG1⁺ Th1 cells that persists poorly and can neither migrate into the lung parenchyma nor control Mtb growth. Furthermore, T-bet suppresses development of CD69⁺CD103⁺ tissue resident phenotype effectors in lung. In contrast, Th1-cell-derived IFN-γ inhibits the accumulation of intravascular CX3CR1⁺KLRG1⁺ Th1 cells. Thus, although IL-12 and T-bet are essential host survival factors, they simultaneously oppose lung CD4 T cell responses at several levels, demonstrating the dual nature of Th1 polarization in tuberculosis.

l-Citrulline Metabolism in Mice Augments CD4+ T Cell Proliferation and Cytokine Production In Vitro, and Accumulation in the Mycobacteria-Infected Lung

Activation, recruitment, and effector function of T lymphocytes are essential for control of mycobacterial infection. These processes are tightly regulated in T cells by the availability of l-arginine within the microenvironment. In turn, mycobacterial infection dampens T cell responsiveness through arginase induction in myeloid cells, promoting sequestration of l-arginine within the local milieu. Here, we show T cells can replenish intracellular l-arginine through metabolism of l-citrulline to mediate inflammatory function, allowing anti-mycobacterial T cells to overcome arginase-mediated suppression. Furthermore, T cell l-citrulline metabolism is necessary for accumulation of CD4⁺ T cells at the site of infection, suggesting this metabolic pathway is involved during anti-mycobacterial T cell immunity in vivo. Together, these findings establish a contribution for l-arginine synthesis by T cells during mycobacterial infection, and implicate l-citrulline as a potential immuno-nutrient to modulate host immunity.

IL-21 Receptor Signaling Is Essential for Optimal CD4+ T Cell Function and Control of Mycobacterium tuberculosis Infection in Mice

In this study, we determined the role of IL-21R signaling in Mycobacterium tuberculosis infection, using IL-21R knockout (KO) mice. A total of 50% of M. tuberculosis H37Rv-infected IL-21R KO mice died in 6 mo compared with no deaths in infected wild type (WT) mice. M. tuberculosis-infected IL-21R KO mice had enhanced bacterial burden and reduced infiltration of Ag-specific T cells in lungs compared with M. tuberculosis-infected WT mice. Ag-specific T cells from the lungs of M. tuberculosis-infected IL-21R KO mice had increased expression of T cell inhibitory receptors, reduced expression of chemokine receptors, proliferated less, and produced less IFN- γ, compared with Ag-specific T cells from the lungs of M. tuberculosis-infected WT mice. T cells from M. tuberculosis-infected IL-21R KO mice were unable to induce optimal macrophage responses to M. tuberculosis. This may be due to a decrease in the Ag-specific T cell population. We also found that IL-21R signaling is associated with reduced expression of a transcriptional factor Eomesodermin and enhanced functional capacity of Ag-specific T cells of M. tuberculosis-infected mice. The sum of our findings suggests that IL-21R signaling is essential for the optimal control of M. tuberculosis infection.

The role of IL-10 in Mycobacterium avium subsp. paratuberculosis infection

Mycobacterium avium subsp. paratuberculosis (MAP) is an intracellular pathogen and is the causative agent of Johne's disease of domestic and wild ruminants. Johne's disease is characterized by chronic granulomatous enteritis leading to substantial economic losses to the livestock sector across the world. MAP persistently survives in phagocytic cells, most commonly in macrophages by disrupting its early antibacterial activity. MAP triggers several signaling pathways after attachment to pathogen recognition receptors (PRRs) of phagocytic cells. MAP adopts a survival strategy to escape the host defence mechanisms via the activation of mitogen-activated protein kinase (MAPK) pathway. The signaling mechanism initiated through toll like receptor 2 (TLR2) activates MAPK-p38 results in up-regulation of interleukin-10 (IL-10), and subsequent repression of inflammatory cytokines. The anti-inflammatory response of IL-10 is mediated through membrane-bound IL-10 receptors, leading to trans-phosphorylation and activation of Janus Kinase (JAK) family receptor-associated tyrosine kinases (TyKs), that promotes the activation of latent transcription factors, signal transducer and activators of transcription 3 (STAT3). IL-10 is an important inhibitory cytokine playing its role in blocking phagosome maturation and apoptosis. In the current review, we describe the importance of IL-10 in early phases of the MAP infection and regulatory mechanisms of the IL-10 dependent pathways in paratuberculosis. We also highlight the strategies to target IL-10, MAPK and STAT3 in other infections caused by intracellular pathogens.

T-bet expression by Th cells promotes type 1 inflammation but is dispensable for colitis

The transcription factor T-bet is highly expressed by Th cells isolated from the inflamed intestine of Crohn's disease patients, and has been regarded a critical driver of murine T cell-induced colitis. However, we show here that T-bet expression by Th cells is not required for the manifestation of T-cell-induced colitis in the presence of segmented filamentous bacteria and Helicobacter hepaticus. T-bet expression by Th cells controls their survival and localization, their repertoire of chemokine and chemokine receptor expression, the accumulation of monocytes and macrophages in the inflamed colon, and their differentiation to the M1 type, i.e., type 1 inflammation. Nevertheless, T-bet-deficient Th cells efficiently induce colitis, as reflected by weight loss, diarrhea, and colon histopathology. T-bet-deficient Th cells differentiate into Th1/17 cells, able to express IFN-γ and IL-17A upon restimulation. While neutralization of IL-17A exacerbated colitis induced by wild-type or T-bet-deficient Th cells, neutralization of IFN-γ completely abolished colitis.

Potential Role of Hepatitis C Virus Alternate Reading Frame Protein in Negative Regulation of T-Bet Gene Expression

Hepatitis C virus (HCV) is a major cause of chronic liver disease and has led to cirrhosis or hepatocellular carcinoma in a majority of infected individuals. We have previously demonstrated that the HCV alternate reading frame protein (F protein) is related to Th1/Th2 bias in chronic hepatitis C (CHC) patients, and we aimed to explore the relative molecular mechanisms here. A total of 104 cases including CHC patients and healthy donors were enrolled. T-bet and GATA-3 expression levels were analyzed in peripheral blood mononuclear cells (PBMCs). The levels of signal transducer and activator of transcription-1/-6(STAT1/6) and phosphorylated STAT1/6(pSTAT1/6) in PBMCs were measured by Western blotting. Our results showed that the levels of T-bet in PBMCs, as well as the levels of gamma interferon (IFN-γ) in sera, were decreased in anti-F protein antibody seropositive patients compared with anti-F protein antibody seronegative patients, whereas the levels of GATA-3 did not show difference between the two groups. Moreover, the decreased pSTAT1 and increased pSTAT6 were observed in PBMCs by HCV core/F protein stimulation with constant STAT1/6 expression. Taken together, it suggested that T-bet may be involved in Th1/Th2 bias induced by HCV F protein, and the disruption of STAT phosphorylation may participate in this mediation.

Genetic association of ankylosing spondylitis with TBX21 influences T-bet and pro-inflammatory cytokine expression in humans and SKG mice as a model of spondyloarthritis

OBJECTIVES

Ankylosing spondylitis (AS) is a highly heritable immune-mediated arthropathy. Inflammation in AS is poorly understood. TBX21 encodes T-bet, a transcription factor, lying within a locus with genome-wide significant association with AS. T-bet is implicated in innate and adaptive immunity. However, the role of T-bet in AS pathogenesis is unclear.

METHODS

We assessed the importance of T-bet in disease development and progression in peripheral blood mononuclear cells from 172 AS cases and 83 healthy controls carrying either risk or protective alleles of the peak AS-associated TBX21 single nucleotide polymorphism. Kinetics and localisation of T-bet expression in the SKG mouse model of spondyloarthropathy was examined, along with the impact of Tbx21 knockout on arthritis development in SKG mice.

RESULTS

Patients with AS had higher T-bet expression than healthy individuals, driven predominantly by natural killer and CD8+ T cells, with expression levels in CD8+ T cells completely distinguishing AS cases from healthy controls. T-bet expression was increased in AS cases carrying risk compared with protective alleles of rs11657479. In curdlan-treated SKG mice, T-bet expression increased early after disease initiation and persisted throughout the course of disease. There was marked reduction in gut and peripheral joint inflammation, and less IFNγ-producing and IL-17-producing CD8+ T cells, in Tbx21-/- compared with wild-type SKG mice.

CONCLUSIONS

AS-associated variants in TBX21 influence T-bet expression. T-bet+ innate and adaptive immune cells have altered IL-17 and IFNγ, and early activation marker CD69 expression than T-bet cells. This indicates that T-bet is a major component of inflammatory pathways of spondyloarthropathy in humans and mice.

Evasion of Innate and Adaptive Immunity by Mycobacterium tuberculosis

Through thousands of years of reciprocal coevolution, Mycobacterium tuberculosis has become one of humanity's most successful pathogens, acquiring 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 that interfere with both innate and adaptive immunity. These include the manipulation of their phagosomal environment within host macrophages, the selective avoidance or engagement of pattern recognition receptors, modulation of host cytokine production, and the manipulation of antigen presentation to prevent or alter the quality of T-cell responses. In this article we review an extensive array of published studies that have begun to unravel the sophisticated program of specific mechanisms that enable M. tuberculosis and other pathogenic mycobacteria to persist and replicate in the face of considerable immunological pressure from their hosts. Unraveling the mechanisms by which M. tuberculosis evades or modulates host immune function is likely to be of major importance for the development of more effective new vaccines and targeted immunotherapy against tuberculosis.

Constitutive expression of SMAR1 confers susceptibility to Mycobacterium tuberculosis infection in a transgenic mouse model

BACKGROUND & OBJECTIVES

Studies involving animal models of experimental tuberculosis have elucidated the predominant role of cytokines secreted by T cells and macrophages to be an essential component of the immune response against Mycobacterium tuberculosis infection. The immune activities of CD4+ T cells are mediated in part by Th1 cytokine interferon gamma (IFN-γ) which is produced primarily by T cells and natural killer (NK) cells and critical for initiating the immune response against intracellular pathogen such as M. tuberculosis. Nuclear matrix protein SMAR1 plays an important role in V(D)J recombination, T helper cell differentiation and inflammatory diseases. In this study a transgenic mouse model was used to study the role of SMAR1 in M. tuberculosis infection.

METHODS

Wild type BALB/c, C57BL/6, BALB/c-EGFP-SMAR1 and C57BL/6-SMAR1 transgenic mice were infected with M. tuberculosis (H37Rv). A dose of 100 bacilli was used for infection via respiratory route. Bacterial load in lung and spleen of infected mice was determined at 2, 4, 6 and 8 wk post-infection. Gene expression analysis for Th1 cytokines and inducible nitric oxide synthase (iNOS) was performed in infected lung tissues by quantitative reverse transcription (RT)-PCR.

RESULTS

SMAR1 transgenic mice from both BALB/c and C57BL/6 genetic background displayed higher bacillary load and susceptibility to M. tuberculosis infection compared to wild type mice. This susceptibility was attributed due to compromised of Th1 response exhibited by transgenic mice.

INTERPRETATION & CONCLUSIONS

SMAR1 transgenic mice exhibited susceptibility to M. tuberculosis infection in vivo irrespective of genetic background. This susceptibility was attributed to downregulation of Th1 response and its hallmark cytokine IFN-γ. Hence, SMAR1 plays an important role in modulating host immune response after M. tuberculosis infection.

Complexity and Controversies over the Cytokine Profiles of T Helper Cell Subpopulations in Tuberculosis

Tuberculosis (TB) is a contagious infectious disease caused by the TB-causing bacillus Mycobacterium tuberculosis and is considered a public health problem with enormous social impact. Disease progression is determined mainly by the balance between the microorganism and the host defense systems. Although the immune system controls the infection, this control does not necessarily lead to sterilization. Over recent decades, the patterns of CD4+ T cell responses have been studied with a goal of complete understanding of the immunological mechanisms involved in the maintenance of latent or active tuberculosis infection and of the clinical cure after treatment. Conflicting results have been suggested over the years, particularly in studies comparing experimental models and human disease. In recent years, in addition to Th1, Th2, and Th17 profiles, new standards of cellular immune responses, such as Th9, Th22, and IFN-γ-IL-10 double-producing Th cells, discussed here, have also been described. Additionally, many new roles and cellular sources have been described for IL-10, demonstrating a critical role for this cytokine as regulatory, rather than merely pathogenic cytokine, involved in the establishment of chronic latent infection, in the clinical cure after treatment and in keeping antibacillary effector mechanisms active to prevent immune-mediated damage.

Elevated expression of T-bet in mycobacterial antigen-specific CD4(+) T cells from patients with tuberculosis

T-bet is a T-box transcriptional factor that controls the differentiation and effector functions of CD4 T cells. In this study, we studied the role of T-bet in regulating CD4(+) T cell immunity against tuberculosis (TB). T-bet expression in Mycobacterium tuberculosis antigen-specific CD4(+) T cells was significantly higher in patients with active TB than in individuals with latent TB infection (p<0.0001). Comparison of T-bet expression in TCM and TEM subsets showed that CD4(+)T-bet(+)M. tuberculosis antigen-specific CD4(+) T cells had significantly lower frequency of TCM (p=0.003) and higher frequency of TEM (p=0.003) than CD4(+)T-bet(-) cells. The expression of PD-1 in antigen-specific CD4(+) T cells was significantly higher in patients with TB than in individuals with latent TB infection (p=0.006). CD4(+)CD154(+)T-bet(+) T cells had significantly higher expression of PD-1 than CD4(+)CD154(+)T-bet(-) T cells (p=0.0028). It is concluded that T-bet expression might be associated with differentiation into effector memory cells and PD-1 expression in mycobacterial antigen-specific CD4(+) T cells.

Innate and Adaptive Cellular Immune Responses to Mycobacterium tuberculosis Infection

Host resistance to Mycobacterium tuberculosis (Mtb) infection requires the coordinated efforts of innate and adaptive immune cells. Diverse pulmonary myeloid cell populations respond to Mtb with unique contributions to both host-protective and potentially detrimental inflammation. Although multiple cell types of the adaptive immune system respond to Mtb infection, CD4 T cells are the principal antigen-specific cells responsible for containment of Mtb infection, but they can also be major contributors to disease during Mtb infection in several different settings. Here, we will discuss the role of different myeloid populations as well as the dual nature of CD4 T cells in Mtb infection with a primary focus on data generated using in vivo cellular immunological studies in experimental animal models and in humans when available.

Expression pattern of transcription factors and intracellular cytokines reveals that clinically cured tuberculosis is accompanied by an increase in Mycobacterium-specific Th1, Th2, and Th17 cells

Tuberculosis (TB) remains a major global health problem and is the second biggest cause of death by infectious disease worldwide. Here, we investigate in vitro the Th1, Th2, Th17, and Treg cytokines and transcriptional factors produced after Mycobacterium-specific antigen stimulation in patients with active pulmonary tuberculosis, clinically cured pulmonary tuberculosis, and healthy donors with a positive tuberculin skin test (TST+). Together, our data indicate that clinical cure after treatment increases the percentages of Mycobacterium-specific Th1, Th2, and Th17 cells compared with those found in active-TB and TST+ healthy donors. These results show that the host-parasite equilibrium in latent TB breaks in favor of the microorganism and that the subsequent clinical recovery posttreatment does not return the percentage levels of such cells to those observed in latent tuberculosis. Additionally, our results indicate that rather than showing an increase in the percentage of Mycobacterium-specific Tregs, active-TB patients display lower Th1 : Treg and Th17 : Treg ratios. These data, together with lower Th1 : Th2 and Th17 : Th2 ratios, may indicate a mechanism by which the breakdown of the host-parasite equilibrium leads to active-TB and changes in the repertoire of Mycobacterium-specific Th cells that are associated with clinical cure after treatment of pulmonary tuberculosis.

Toll-like receptor 2-dependent extracellular signal-regulated kinase signaling in Mycobacterium tuberculosis-infected macrophages drives anti-inflammatory responses and inhibits Th1 polarization of responding T cells

Mycobacterium tuberculosis survives within macrophages and employs immune evasion mechanisms to persist in the host. Protective T helper type 1 (Th1) responses are induced, and the immune response in most individuals is sufficient to restrict M. tuberculosis to latent infection, but most infections are not completely resolved. As T cells and macrophages respond, a balance is established between protective Th1-associated and other proinflammatory cytokines, such as interleukin-12 (IL-12), interferon gamma (IFN-γ), and tumor necrosis factor alpha, and anti-inflammatory cytokines, such as IL-10. The mechanisms by which M. tuberculosis modulates host responses to promote its survival remain unclear. In these studies, we demonstrate that M. tuberculosis induction of IL-10, suppression of IL-12, and inhibition of class II major histocompatibility complex (MHC-II) molecules in infected macrophages are all driven by Toll-like receptor 2 (TLR2)-dependent activation of the extracellular signal-regulated kinases (ERK). Elimination of ERK signaling downstream of TLR2 by pharmacologic inhibition with U0126 or genetic deletion of Tpl2 blocks IL-10 secretion and enhances IL-12 p70 secretion. We demonstrate that M. tuberculosis regulation of these pathways in macrophages affects T cell responses to infected macrophages. Thus, genetic blockade of the ERK pathway in Tpl2(-/-) macrophages enhances Th1 polarization and IFN-γ production by antigen-specific CD4(+) T cells responding to M. tuberculosis infection. These data indicate that M. tuberculosis and its potent TLR2 ligands activate ERK signaling in macrophages to promote anti-inflammatory macrophage responses and blunt Th1 responses against the pathogen.

TBX21 polymorphisms are associated with virus persistence in hepatitis C virus infection patients from a high-risk Chinese population

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease and the varied outcomes of the infection depend on both viral and host factors. We have demonstrated that the HCV alternate reading frame protein (F protein) is related to Th1/Th2 bias which is involved in virus persistence in chronic hepatitis C (CHC) patients. The purpose of this study was to test the hypothesis that genetic variants of TBX21 (T cell specific T-box transcription factor) were associated with the outcomes of HCV infection and F protein generation. Three single nucleotide polymorphisms (SNPs) (rs17250932, rs2074190, rs4794067) in the TBX21 gene were genotyped in a case-control study in a cohort of a high-risk group, including 354 healthy controls and 747 CHC patients (190 anti-F protein antibody seronegative patients and 557 anti-F protein antibody seropositive patients). Results showed that the rs4794067 C allele in the TBX21 promoter was significantly more common in CHC patients (OR = 1.335, 95% CI = 1.058-1.684, P = 0.015), exceptionally in anti-F protein seropositive patients (OR = 1.547, 95% CI = 1.140-2.101, P = 0.005), compared with healthy controls. And the risk effect was also significantly high in patients with HCV 1b genotype and mild fibrosis (P = 0.021, P = 0.010, respectively). Compared with the most frequent haplotype TAT, haplotype analysis showed that the distribution of TAC was significantly different between the chronic HCV carrier group and the healthy group, and so was the anti-F antibody seronegativity group and the anti-F antibody seronegativity group (all P < 0.001). Our results suggested that TBX21 variants may be involved in the etiology of this disease.

Diverse roles for T-bet in the effector responses required for resistance to infection

The transcription factor T-bet has been most prominently linked to NK and T cell production of IFN-γ, a cytokine required for the control of a diverse array of intracellular pathogens. Indeed, in mice challenged with the parasite Toxoplasma gondii, NK and T cell responses are characterized by marked increases of T-bet expression. Unexpectedly, T-bet(-/-) mice infected with T. gondii develop a strong NK cell IFN-γ response that controls parasite replication at the challenge site, but display high parasite burdens at secondary sites colonized by T. gondii and succumb to infection. The loss of T-bet had a modest effect on T cell production of IFN-γ but did not impact on the generation of parasite-specific T cells. However, the absence of T-bet resulted in lower T cell expression of CD11a, Ly6C, KLRG-1, and CXCR3 and fewer parasite-specific T cells at secondary sites of infection, associated with a defect in parasite control at these sites. Together, these data highlight T-bet-independent pathways to IFN-γ production and reveal a novel role for this transcription factor in coordinating the T cell responses necessary to control this infection in peripheral tissues.

Defining features of protective CD4 T cell responses to Mycobacterium tuberculosis

CD4 T cells are critical for control of Mycobacterium tuberculosis (Mtb) infection and represent the best hope for vaccine-elicited protection. However, little is understood about the properties of Mtb-specific CD4 T cells that mediate control, and the lack of correlates of protection present a significant barrier to the rational development of new vaccination and therapeutic strategies which are sorely needed. Here we discuss the features of protective CD4 T cells including recent evidence for IFN-γ dependent and independent mechanisms of protection, poor protection by terminally differentiated cells and the importance of T cell migratory capacity for the control of Mtb infection.

The role of protein modifications of T-bet in cytokine production and differentiation of T helper cells

T-Bet (T-box protein expressed in T cells, also called as TBX21) was originally cloned as a key transcription factor involved in the commitment of T helper (Th) cells to the Th1 lineage. T-Bet directly activates IFN-γ gene transcription and enhances development of Th1 cells. T-Bet simultaneously modulates IL-2 and Th2 cytokines in an IFN-γ-independent manner, resulting in an attenuation of Th2 cell development. Numerous studies have demonstrated that T-bet plays multiple roles in many subtypes of immune cells, including B cell, dendritic cells, natural killer (NK) cells, NK T cells, and innate lymphoid cells. Therefore, T-bet is crucial for the development and coordination of both innate and adaptive immune responses. To fulfill these multiple roles, T-bet undergoes several posttranslational protein modifications, such as phosphorylation at tyrosine, serine, and threonine residues, and ubiquitination at lysine residues, which affect lineage commitment during Th cell differentiation. This review presents a current overview of the progress made in understanding the roles of various types of T-bet protein modifications in the regulation of cytokine production during Th cell differentiation.

Cutting edge: control of Mycobacterium tuberculosis infection by a subset of lung parenchyma-homing CD4 T cells

Th1 cells are critical for containment of Mycobacterium tuberculosis infection, but little else is known about the properties of protective CD4 T cell responses. In this study, we show that the pulmonary Th1 response against M. tuberculosis is composed of two populations that are either CXCR3(hi) and localize to lung parenchyma or are CX3CR1(hi)KLRG1(hi) and are retained within lung blood vasculature. M. tuberculosis-specific parenchymal CD4 T cells migrate rapidly back into the lung parenchyma upon adoptive transfer, whereas the intravascular effectors produce the highest levels of IFN-γ in vivo. Importantly, parenchymal T cells displayed greater control of infection compared with the intravascular counterparts upon transfer into susceptible T cell-deficient hosts. Thus, we identified a subset of naturally generated M. tuberculosis-specific CD4 T cells with enhanced protective capacity and showed that control of M. tuberculosis correlates with the ability of CD4 T cells to efficiently enter the lung parenchyma rather than produce high levels of IFN-γ.