Reduced expression of nuclear cyclic adenosine 5'-monophosphate response element-binding proteins and IFN-gamma promoter function in disease due to an intracellular pathogen

Association of IFN-γ +874 A/T SNP and hypermethylation of the -53 CpG site with tuberculosis susceptibility

Introduction

Tuberculosis (TB) is now the 2nd leading infectious killer after COVID-19 and the 13th leading cause of death worldwide. Moreover, TB is a lethal combination for HIV-patients. Th1 responses and particularly IFN-γ are crucial for immune protection against Mycobacterium tuberculosis infection. Many gene variants for IFNG that confer susceptibility to TB have been described in multiple ethnic populations. Likewise, some epigenetic modifications have been evaluated, being CpG methylation the major epigenetic mark that makes chromatin inaccessible to transcription factors, thus avoiding the initiation of IFNG transcription.

Methods

We evaluated both genetic and epigenetic changes involved in IFN-γ production and TB susceptibility in Argentine population. Amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) was performed for the IFN-γ +874 A/T polymorphism (rs2430561) genotyping in 199 healthy donors (HD) and 173 tuberculosis (TB) patients. IFN-γ levels from M. tuberculosis-stimulated PBMCs were measured by ELISA. The methylation status at the -53 CpG site of the IFNG promoter in individuals with latent infection (LTBI), TB and HD was determine by pyrosequencing.

Results

Using a case-control study, we found that A allele and, consequently, AA genotype were overrepresented in patients with active disease. Moreover, HD carrying T allele (AT or TT genotype) evidenced an augmented IFN-γ secretion compared to TB patients. Codominance was the genetic model that best fits our results according to the Akaike information criterion (AIC). In addition, increased methylation levels at the -53 CpG site in the IFN-γ promoter were observed in whole blood of patients with active TB compared to LTBI individuals.

Discussion

IFN-γ is regulated by genetic variants and epigenetic modifications during TB. Besides, AA genotype of the rs2430561 single nucleotide polymorphism could be considered as a potential TB susceptibility genetic biomarker in Argentina and the methylation of the -53 CpG site could result in a useful predictor of TB reactivation.

Elevated Cyclic AMP Inhibits Mycobacterium tuberculosis-Stimulated T-cell IFN-γ Secretion Through Type I Protein Kinase A

Cyclic adenosine monophosphate (cAMP) is critical in immune regulation, and its role in tuberculosis infection remains unclear. We determined the levels of cAMP in peripheral blood mononuclear cells (PBMC) from tuberculosis patients and the mechanisms for cAMP suppression of IFN-γ production. PBMC from tuberculosis patients contained significantly elevated cAMP than latent tuberculosis infected subjects (LTBI), with an inverse correlation with IFN-γ production. Consistent with this, the expression of cAMP response element binding protein (CREB), activating transcription factor (ATF)-2 and c-Jun were reduced in tuberculosis patients compared with LTBI. PKA type I specific cAMP analogs inhibited Mtb-stimulated IFN-g production by PBMC through suppression of Mtb-induced IFN-γ promoter binding activities of CREB, ATF-2, and c-Jun and also miR155, the target miRNA of these transcription factors. Neutralizing both IL-10 and TGF-β1 or supplementation of IL-12 restored cAMP-suppressed IFN-g production. We conclude that increased cAMP inhibits IFN-g production through PKA type I pathway in tuberculosis infection.

ERAP1 and PDE8A Are Downregulated in Cattle Protected against Bovine Tuberculosis

Bovine tuberculosis (bTB) is a zoonotic disease caused by Mycobacterium bovis that is responsible for significant economic losses worldwide. In spite of its relevance, the limited knowledge about the host immune responses that provide effective protection against the disease has long hampered the development of an effective vaccine. The identification of host proteins with an expression that correlates with protection against bTB would contribute to the understanding of the cattle defence mechanisms against M. bovis infection. In this study, we found that ERAP1 and PDE8A were downregulated in vaccinated cattle that were protected from experimental M. bovis challenge. Remarkably, both genes encode proteins that have been negatively associated with immune protection against bTB.

Early Secreted Antigenic Target of 6-kDa of Mycobacterium tuberculosis Stimulates IL-6 Production by Macrophages through Activation of STAT3

As early secreted antigenic target of 6 kDa (ESAT-6) of Mycobacterium tuberculosis (Mtb) is an essential virulence factor and macrophages are critical for tuberculosis infection and immunity, we studied ESAT-6 stimulated IL-6 production by macrophages. ESAT-6 stimulated significantly higher IL-6 secretion by murine bone marrow derived macrophages (BMDM) compared to culture filtrate protein 10 kDa (CFP10) and antigen 85A. Polymyxin B, an LPS blocker, did not affect ESAT-6 stimulated macrophage IL-6 production. ESAT-6 but not Pam3CSK4 induced IL-6 by TLR2 knockout BMDM. ESAT-6 induced phosphorylation and DNA binding of STAT3 and this was blocked by STAT3 inhibitors but not by rapamycin. STAT3 inhibitors suppressed ESAT-6-induced IL-6 transcription and secretion without affecting cell viability. This was confirmed by silencing STAT3 in macrophages. Blocking neither IL-6Rα/IL-6 nor IL-10 affected ESAT-6-induced STAT3 activation and IL-6 production. Infection of BMDM and human macrophages with Mtb with esat-6 deletion induced diminished STAT3 activation and reduced IL-6 production compared to wild type and esat-6 complemented Mtb strains. Administration of ESAT-6 but not CFP10 induced STAT3 phosphorylation and IL-6 expression in the mouse lungs, consistent with expression of ESAT-6, IL-6 and phosphorylated-STAT3 in Mtb-infected mouse lungs. We conclude that ESAT-6 stimulates macrophage IL-6 production through STAT3 activation.

IFNG-mediated immune responses enhance autophagy against Mycobacterium tuberculosis antigens in patients with active tuberculosis

Protective immunity against Mycobacterium tuberculosis (Mtb) requires IFNG. Besides, IFNG-mediated induction of autophagy suppresses survival of virulent Mtb in macrophage cell lines. We investigated the contribution of autophagy to the defense against Mtb antigen (Mtb-Ag) in cells from tuberculosis patients and healthy donors (HD). Patients were classified as high responders (HR) if their T cells produced significant IFNG against Mtb-Ag; and low responders (LR) when patients showed weak or no T cell responses to Mtb-Ag. The highest autophagy levels were detected in HD cells whereas the lowest quantities were observed in LR patients. Interestingly, upon Mtb-Ag stimulation, we detected a positive correlation between IFNG and MAP1LC3B-II/LC3-II levels. Actually, blockage of Mtb-Ag-induced IFNG markedly reduced autophagy in HR patients whereas addition of limited amounts of IFNG significantly increased autophagy in LR patients. Therefore, autophagy collaborates with human immune responses against Mtb in close association with specific IFNG secreted against the pathogen.

Phosphorylation of mitogen-activated protein kinases contributes to interferon γ production in response to Mycobacterium tuberculosis

Immune control of Mycobacterium tuberculosis depends on interferon γ (IFN-γ)-producing CD4(+) lymphocytes. Previous studies have shown that T cells from patients with tuberculosis produce less IFN-γ, compared with healthy donors, in response to mycobacterial antigens, although IFN-γ responses to mitogens are preserved. In this work, we found that M. tuberculosis-induced IFN-γ production by human T cells correlated with phosphorylation of the mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase (ERK), and p38. Moreover, the majority of IFN-γ-producing T cells expressed signaling lymphocyte activation molecule (SLAM), and SLAM activation further increased ERK phosphorylation. Interestingly, patients with tuberculosis had delayed activation of ERK and p38, and this was most marked in patients with the poorest IFN-γ responses (ie, low responders). Besides, SLAM signaling failed to phosphorylate ERK in low responders. Our findings suggest that activation of p38 and ERK, in part through SLAM, mediates T-cell IFN-γ production in response to M. tuberculosis, a pathway that is defective in patients with tuberculosis.

Early secreted antigenic target of 6-kDa protein of Mycobacterium tuberculosis primes dendritic cells to stimulate Th17 and inhibit Th1 immune responses

Early secreted antigenic target of 6 kDa (ESAT-6) of Mycobacterium tuberculosis is a T cell Ag that is a potential vaccine candidate, but it is also a virulence factor that mediates pathogenicity. To better understand the effects of ESAT-6 on the immune response, we studied the effect of ESAT-6 on human dendritic cells (DCs). Peripheral blood monocytes were treated with GM-CSF and IL-4 to yield immature DCs, which were matured by addition of LPS and CD40 ligand (CD40L), with or without ESAT-6. ESAT-6 inhibited LPS/CD40L-induced DC expression of costimulatory molecules, reduced DC-stimulated allogeneic T cell proliferation and IL-2 and IFN-γ production, and enhanced IL-17 production. ESAT-6-treated DCs also increased IL-17 and reduced IFN-γ production by M. tuberculosis-specific autologous T cells. ESAT-6 inhibited LPS/CD40L-induced DC production of IL-12 and enhanced that of IL-23 and IL-1β, without affecting secretion of TNF-α, IL-6, or IL-8 through specific interaction with immature DCs. The effects of ESAT-6 were not mediated through cAMP or p38 MAPK. Medium from ESAT-6-conditioned DCs increased IL-17 and reduced IFN-γ production by T cells stimulated with anti-CD3 plus anti-CD28, and ESAT-6-induced IL-17 production was blocked by neutralizing both IL-23 and IL-1β. ESAT-6 reduced LPS/CD40L-stimulated transcription of IL-12p35 and enhanced that of IL-23p19 through inhibition of IFN regulatory factor-1 and upregulation of activating transcription factor-2 and c-Jun, transcriptional regulators of IL-12p35 and IL-23p19, respectively. We conclude that ESAT-6 increases DC production of IL-23 and IL-1β while inhibiting that of IL-12, thus enhancing Th17 at the expense of protective Th1 responses.

Progress in understanding the human immune responses to Mycobacterium tuberculosis

Development of an effective vaccine against tuberculosis hinges on an improved understanding of the human immune response to Mycobacterium tuberculosis. Work in this area at the University of Texas Health Science Center at Tyler has led to advances in four areas: (1) natural killer cells contribute to innate immunity by lysing M. tuberculosis-infected mononuclear phagocytes, and to adaptive immunity by enhancing the CD8+ T-cell effector function and inhibiting expansion of T regulatory cells; (2) Interferon-gamma plays a central role in resistance to many intracellular pathogens, including M. tuberculosis, and we have identified three transcription factors that bind to the Interferon-gamma proximal promoter and increase Interferon-gamma transcription in live T-cells that are activated by M. tuberculosis antigens; (3) A DNA vaccine that encodes the M. tuberculosis 10fts;kDa culture filtrate protein and the lysosomal integral membrane protein-2 was produced to direct vaccine antigens to the MHC class II processing and presentation pathway. When this vaccine was coated with polyethylenimine and administered to mice, it yielded a remarkably potent pulmonary immune response that reduced the bacillary burden by 90% after M. tuberculosis challenge; (4) The early secreted antigenic target of 6fts;kDa (ESAT-6) is a putative vaccine antigen. We found that high concentrations of this antigen markedly inhibit Interferon-gamma production by T-cells and are working to understand the molecular mechanisms underlying this effect. Developing methods to enhance NK cell functions that favor protective immunity, increase interferon-gamma transcription, elicit protective pulmonary immune responses and prevent ESAT-6 from inhibiting T-cell function will contribute significantly to development of antituberculosis vaccines.

β-Caryophyllene inhibits dextran sulfate sodium-induced colitis in mice through CB2 receptor activation and PPARγ pathway

Cannabinoid receptor 2 (CB2) activation is suggested to trigger the peroxisome proliferator-activated receptor-γ (PPARγ) pathway, and agonists of both receptors improve colitis. Recently, the plant metabolite (E)-β-caryophyllene (BCP) was shown to bind to and activate CB2. In this study, we examined the anti-inflammatory effect of BCP in dextran sulfate sodium (DSS)-induced colitis and analyzed whether this effect was mediated by CB2 and PPARγ. Oral treatment with BCP reduced disease activity, colonic macro- and microscopic damage, myeloperoxidase and N-acetylglucosaminidase activities, and levels and mRNA expression of colonic tumor necrosis factor-α, IL-1β, interferon-γ, and keratinocyte-derived chemokine. BCP treatment also inhibited the activation of extracellular signal-regulated kinase 1/2, nuclear factor κB, IκB-kinase α/β, cAMP response element binding and the expression of caspase-3 and Ki-67. Moreover, BCP enhanced IL-4 levels and forkhead box P3 mRNA expression in the mouse colon and reduced cytokine levels (tumor necrosis factor-α, keratinocyte-derived chemokine, and macrophage-inflammatory protein-2) in a culture of macrophages stimulated with lipopolysaccharide. The use of the CB2 antagonist AM630 or the PPARγ antagonist GW9662 significantly reversed the protective effect of BCP. Confirming our results, AM630 reversed the beneficial effect of BCP on pro-inflammatory cytokine expression in IEC-6 cells. These results demonstrate that the anti-inflammatory effect of BCP involves CB2 and the PPARγ pathway and suggest BCP as a possible therapy for the treatment of inflammatory bowel disease.

Exposure to cigarette smoke inhibits the pulmonary T-cell response to influenza virus and Mycobacterium tuberculosis

Smoking is associated with increased susceptibility to tuberculosis and influenza. However, little information is available on the mechanisms underlying this increased susceptibility. Mice were left unexposed or were exposed to cigarette smoke and then infected with Mycobacterium tuberculosis by aerosol or influenza A by intranasal infection. Some mice were given a DNA vaccine encoding an immunogenic M. tuberculosis protein. Gamma interferon (IFN-γ) production by T cells from the lungs and spleens was measured. Cigarette smoke exposure inhibited the lung T-cell production of IFN-γ during stimulation in vitro with anti-CD3, after vaccination with a construct expressing an immunogenic mycobacterial protein, and during infection with M. tuberculosis and influenza A virus in vivo. Reduced IFN-γ production was mediated through the decreased phosphorylation of transcription factors that positively regulate IFN-γ expression. Cigarette smoke exposure increased the bacterial burden in mice infected with M. tuberculosis and increased weight loss and mortality in mice infected with influenza virus. This study provides the first demonstration that cigarette smoke exposure directly inhibits the pulmonary T-cell response to M. tuberculosis and influenza virus in a physiologically relevant animal model, increasing susceptibility to both pathogens.

CREB is a positive transcriptional regulator of gamma interferon in latent but not active tuberculosis infections

Gamma interferon (IFN-gamma) is a crucial cytokine for protection against Mycobacterium tuberculosis, but the mechanism of IFN-gamma transcription is still unclear. The cyclic AMP (cAMP) responsive element binding (CREB) proteins belong to the bZip (basic leucine zipper) family of transcription factors and are essential for T-cell function and cytokine production. This study focused on the capacity of CREB proteins to regulate IFN-gamma transcription in CD3(+) T cells obtained from tuberculosis (TB) patients and persons with latent tuberculosis infection (LTBI) in China. The electrophoretic mobility shift assay (EMSA), chromatin immunoprecipitation (ChIP), and Western blotting were used to demonstrate the regulatory role of CREB. EMSA (in vitro) and ChIP (in vivo) experiments suggested CREB could bind to the IFN-gamma proximal promoter in persons with LTBI, whereas no binding was detected in TB patients. Western blotting confirmed the expression of CREB proteins, especially serine-133-phosphorylated CREB, was markedly reduced in TB patients compared with persons with LTBI. These results suggested that CREB could promote the transcription and production of IFN-gamma through binding with the IFN-gamma proximal promoter, but the regulatory role of CREB was decreased in tuberculosis patients owing to diminished expression of CREB proteins, which in turn reduced the IFN-gamma production.

ESAT-6 inhibits production of IFN-gamma by Mycobacterium tuberculosis-responsive human T cells

The Mycobacterium tuberculosis early secreted Ag of 6 kDa (ESAT-6) is a potent Ag for human T cells and is a putative vaccine candidate. However, ESAT-6 also contributes to virulence in animal models, mediates cellular cytolysis, and inhibits IL-12 production by mononuclear phagocytes. We evaluated the effects of ESAT-6 and its molecular chaperone, culture filtrate protein of 10 kDa (CFP10), on the capacity of human T cells to produce IFN-gamma and proliferate in response to TCR activation. Recombinant ESAT-6, but not CFP10, markedly inhibited IFN-gamma production by T cells stimulated with M. tuberculosis or with the combination of anti-CD3 and anti-CD28, in a dose-dependent manner. ESAT-6 also inhibited T cell production of IL-17 and TNF-alpha but not IL-2. Preincubation of ESAT-6 with CFP10 under conditions that favor dimer formation did not affect inhibition of IFN-gamma. ESAT-6 decreased IFN-gamma transcription and reduced expression of the transcription factors, ATF-2 and c-Jun, which normally bind to the IFN-gamma proximal promoter and stimulate mRNA expression. ESAT-6 inhibited T cell IFN-gamma secretion through mechanisms that did not involve cellular cytotoxicity or apoptosis. ESAT-6, but not CFP10, bound to T cells and inhibited expression of early activation markers without reducing activation of ZAP70. We conclude that ESAT-6 directly inhibits human T cell responses to mycobacterial Ags by affecting TCR signaling pathways downstream of ZAP70.

CREB, ATF, and AP-1 transcription factors regulate IFN-gamma secretion by human T cells in response to mycobacterial antigen

IFN-gamma production by T cells is pivotal for defense against many pathogens, and the proximal promoter of IFN-gamma, -73 to -48 bp upstream of the transcription start site, is essential for its expression. However, transcriptional regulation mechanisms through this promoter in primary human cells remain unclear. We studied the effects of cAMP response element binding protein/activating transcription factor (CREB/ATF) and AP-1 transcription factors on the proximal promoter of IFN-gamma in human T cells stimulated with Mycobacterium tuberculosis. Using EMSA, supershift assays, and promoter pulldown assays, we demonstrated that CREB, ATF-2, and c-Jun, but not cyclic AMP response element modulator, ATF-1, or c-Fos, bind to the proximal promoter of IFN-gamma upon stimulation, and coimmunoprecipitation indicated the possibility of interaction among these transcription factors. Chromatin immunoprecipitation confirmed the recruitment of these transcription factors to the IFN-gamma proximal promoter in live Ag-activated T cells. Inhibition of ATF-2 activity in T cells with a dominant-negative ATF-2 peptide or with small interfering RNA markedly reduced the expression of IFN-gamma and decreased the expression of CREB and c-Jun. These findings suggest that CREB, ATF-2, and c-Jun are recruited to the IFN-gamma proximal promoter and that they up-regulate IFN-gamma transcription in response to microbial Ag. Additionally, ATF-2 controls expression of CREB and c-Jun during T cell activation.

An antibody against the surfactant protein A (SP-A)-binding domain of the SP-A receptor inhibits T cell-mediated immune responses to Mycobacterium tuberculosis

Surfactant protein A (SP-A) suppresses lymphocyte proliferation and IL-2 secretion, in part, by binding to its receptor, SP-R210. However, the mechanisms underlying this effect are not well understood. Here, we studied the effect of antibodies against the SP-A-binding (neck) domain (alpha-SP-R210n) or nonbinding C-terminal domain (alpha-SP-R210ct) of SP-R210 on human peripheral blood T cell immune responses against Mycobacterium tuberculosis. We demonstrated that both antibodies bind to more than 90% of monocytes and 5-10% of CD3+ T cells in freshly isolated PBMC. Stimulation of PBMC from healthy tuberculin reactors [purified protein derivative-positive (PPD+)] with heat-killed M. tuberculosis induced increased antibody binding to CD3+ cells. Increased antibody binding suggested enhanced expression of SP-R210, and this was confirmed by Western blotting. The antibodies (alpha-SP-R210n) cross-linking the SP-R210 through the SP-A-binding domain markedly inhibited cell proliferation and IFN-gamma secretion by PBMC from PPD+ donors in response to heat-killed M. tuberculosis, whereas preimmune IgG and antibodies (alpha-SP-R210ct) cross-linking SP-R210 through the non-SP-A-binding, C-terminal domain had no effect. Anti-SP-R210n also decreased M. tuberculosis-induced production of TNF-alpha but increased production of IL-10. Inhibition of IFN-gamma production by alpha-SP-R210n was abrogated by the combination of neutralizing antibodies to IL-10 and TGF-beta1. Together, these findings support the hypothesis that SP-A, via SP-R210, suppresses cell-mediated immunity against M. tuberculosis via a mechanism that up-regulates secretion of IL-10 and TGF-beta1.

Regulation of the alpha-crystallin gene acr2 by the MprAB two-component system of Mycobacterium tuberculosis

Coordinated regulation of molecular chaperones is an important feature of the bacterial stress response. The small molecular chaperone gene acr2 of Mycobacterium tuberculosis is activated by exposure to several stresses, including heat and the detergent sodium dodecyl sulfate (SDS). In this study, we show that acr2 is directly regulated by the MprAB two-component system, and that MprAB has both positive and negative effects on acr2 expression. mRNA analyses showed that acr2 expression levels were lower under SDS stress and control conditions but higher under heat shock in an mprAB deletion mutant than they were in the parental strain. Parental expression patterns were restored in an mprAB-complemented strain. Western blotting using an anti-Acr2 antibody showed that Acr2 protein synthesis correlated with mRNA levels. Primer extension identified one transcriptional start point (TSP) for acr2 in all three strains under control and stress conditions. Electrophoresis mobility shift assays revealed multiple MprA binding sites in the acr2 promoter, including one downstream and three upstream of the acr2 TSP, with one overlapping the binding sites predicted for SigE, SigH, and HspR. DNA footprinting confirmed that MprA protected large sections of the acr2 promoter region. Expression of several housekeeping genes under SDS stress also was evaluated, revealing the upregulation of large molecular chaperone genes and, unexpectedly, sigA, with slightly lower sigA mRNA levels detected in the mprAB deletion mutant than in the wild type. In contrast to Acr2, SigA protein synthesis did not correlate with mRNA expression. Overall, the data indicated that MprA has complex interactions with the acr2 promoter and indirect effects on major housekeeping genes.

Evidence for complex interactions of stress-associated regulons in an mprAB deletion mutant of Mycobacterium tuberculosis

Two-component systems are important constituents of bacterial regulatory networks. Results of this investigation into the role of the MprAB two-component system of Mycobacterium tuberculosis indicate that it is associated with the regulation of several stress-responsive regulons. Using a deletion mutant lacking portions of the response regulator, MprA, and the histidine kinase, MprB, it was demonstrated by real-time PCR, primer extension analyses and DNA microarrays that MprAB activates sigma factor genes sigE and sigB, under SDS stress and during exponential growth. SDS-inducible, MprA-dependent transcriptional start points were identified for mprA, sigE and sigB, and variations in distance between these points and MprA-binding sites suggest that MprA is involved in different mechanisms of promoter activation. Although most of the SigE regulon was downregulated in the deletion mutant, the cluster of genes Rv1129c, Rv1130 and Rv1131, which is associated with growth in monocytes, was upregulated in the deletion mutant under SDS stress, and this upregulation was dependent upon atmospheric growth conditions. Multiple stress-associated genes of the DosR, SigD and IdeR regulons were also upregulated in the deletion mutant, during exponential growth and/or in the presence of SDS. Surprisingly, the deletion mutant had increased resistance to SDS compared to the parental strain, and enhanced growth in human peripheral blood monocytes, characteristics which may result from a loss of repression of stress-associated genes.

Activating Transcription Factor/cAMP Response Element Binding Protein Family Member Regulated Transcription of CD1A

CD1a has a unique expression pattern among Ag-presenting molecules, expressed specifically on cortical thymocytes and APCs. As autoimmune disease, infection, and tumors can all result in alteration of CD1a expression, we are attempting to characterize the transcriptional regulation, and thus shed some light on specific expression, of CD1A. In this study, we have identified a minimal proximal promoter region required for CD1A transcription. Computer searches within this region identified numerous potential binding sites for lymphoid-specific transcription factors, including the ETS transcription factors, C/EBP, GATA, and CREB. Deletion and site-specific mutant analysis revealed a critical role of a potential cAMP response element (CRE) 965 bp upstream of the CD1A translation start site. Two activating transcription factor (ATF)/CREB family members, CREB-1 and ATF-2, are able to bind this site in vitro and in vivo. Notably, activation of ATF/CREB family members decreases CD1A transcription, while decrease in ATF-2 expression results in increased CD1A RNA level. The fact that these factors also bind the CD1A promoter in human monocytes strongly suggests a role for ATF/CREB family members in regulation of CD1A expression.

Association of interferon gamma and interleukin 10 genes with tuberculosis in Hong Kong Chinese

Interferon gamma (IFN-gamma) and interleukin 10 (IL-10) are believed to play opposing roles in host immunity against mycobacterial infection. IFN-gamma activates macrophages, while IL-10 downregulates the expression of T helper type 1 cytokines, MHC class II antigens and costimulatory molecules on macrophages. Associations of IFN-gamma -179 (G/T), +874 (A/T), +875 miscrosatellite CA repeats and +4766 (C/T), and IL-10 -1082 (A/G), -819 (C/T) and -592 (C/A) with tuberculosis (TB) were investigated in 385 HIV-negative patients and 451 controls in a Hong Kong Chinese population. The frequency of a low IFN-gamma-producing +874 A/A genotype was significantly over-represented in the patient group (P<0.001, OR=3.79, 95% CI=1.93-7.45). We identified 10 alleles in the IFN-gamma CA repeats and observed a significant difference in allele frequency distribution between patients and controls (P<0.001). By grouping alleles into 12 and non-12 CA repeats, the non-12/non-12 genotype yielded a similar significant result (P<0.001, OR=4.56, 95% CI=2.21-9.43) as observed in +874 A/A genotype. Weak associations of the IL-10 GCC/- genotype (P=0.04) and the low IFN-gamma-producing A/A genotype (P=0.06) with TB relapse/extrapulmonary cases were found. This study suggests the possible role of interferon gamma in TB susceptibility.

Cyclic AMP Response Element-Binding Protein Positively Regulates Production of IFN-γ by T Cells in Response to a Microbial Pathogen

IFN-gamma is essential for resistance to many intracellular pathogens, including Mycobacterium tuberculosis. Transcription of the IFN-gamma gene in activated T cells is controlled by the proximal promoter element (-73 to -48 bp). CREB binds to the IFN-gamma proximal promoter, and binding is enhanced by phosphorylation of CREB. Studies in human T cell lines and in transgenic mice have yielded conflicting results about whether CREB is a positive or a negative regulator of IFN-gamma transcription. To determine the role of CREB in mediating IFN-gamma production in response to a microbial pathogen, we evaluated the peripheral blood T cell response to M. tuberculosis in healthy tuberculin reactors. EMSAs, chromatin immunoprecipitation, and Western blotting demonstrated that stimulation of PBMC with M. tuberculosis induced phosphorylation and enhanced binding of CREB to the IFN-gamma proximal promoter. Neutralization of CREB with intracellular Abs or down-regulation of CREB levels with small interfering RNA decreased M. tuberculosis-induced production of IFN-gamma and IFN-gamma mRNA expression. In addition, M. tuberculosis-stimulated T cells from tuberculosis patients, who have ineffective immunity, showed diminished IFN-gamma production, reduced amounts of CREB binding to the IFN-gamma proximal promoter, and absence of phosphorylated CREB. These findings demonstrate that CREB positively regulates IFN-gamma production by human T cells that respond to M. tuberculosis.

Effect of promoter methylation on the regulation of IFN-gamma gene during in vitro differentiation of human peripheral blood T cells into a Th2 population

The carefully orchestrated events that result in a protective immune response are coordinated to a large extent by cytokines produced by Th1 and Th2 cell subsets. Th1 cells preferentially produce IL-2 and IFN-gamma, resulting in a cellular response that helps to eliminate infected cells. In contrast, Th2 cells produce IL-4, IL-5, IL-6, and IL-10, stimulating an Ab response that attacks extracellular pathogens, thereby preventing the cells from becoming infected. To elucidate the mechanisms of differential regulation of cytokine genes by these two different subsets of T cells, we established an in vitro differentiation model of freshly isolated human peripheral blood T cells in which IFN-gamma was used as an index gene to study the transcriptional regulation. The data presented here demonstrate that the IFN-gamma promoter undergoes differential methylation during in vitro differentiation: the promoter becomes hypermethylated in Th2 cells, whereas it is hypomethylated in Th1 cells. Hypermethylation in Th2 cells results in chromatin condensation and exclusion of CREB proteins from the IFN-gamma promoter. Treatment with 5-azacytidine, a demethylating agent, causes Th2 cells to reverse histone condensation and enables CREB recruitment to the hypomethylated promoter. This results in the increased production of IFN-gamma. These data indicate the importance of promoter methylation in the regulation of the IFN-gamma gene during differentiation.

Dynamics of cytokine generation in patients with active pulmonary tuberculosis

PURPOSE OF REVIEW

Cytokines have been implicated in the protective immunity, pathophysiology and development of tuberculosis. Most people who become infected with Mycobacterium tuberculosis mount an effective protective immune response, but 5-10% develop disease. Active pulmonary tuberculosis can be considered to reflect an ineffective immune response against mycobacterial infection. A better understanding of how cytokine production contributes to immunity and pathology would aid the development of new vaccines and therapeutic strategies.

RECENT FINDINGS

At the time of diagnosis, production of M. tuberculosis or mycobacterial antigen-induced interferon-gamma by peripheral blood mononuclear cells from tuberculosis patients is usually depressed, compared with that of healthy control subjects, whereas cytokine production at the site of disease is elevated. In most patients, depressed interferon-gamma production by peripheral blood mononuclear cells seems to be a transient response because it is significantly increased in most active tuberculosis patients during and following successful antituberculous therapy. However, some patients remain anergic in vivo and in vitro after chemotherapy, and the underlying biochemical mechanisms for T cell anergy in modulating protection or pathology in tuberculosis needs further clarification. Among the cytokines contributing to protective immunity, interleukins 12 and 18, and tumour necrosis factor-alpha are important, the basis of recent studies with tuberculosis patients.

SUMMARY

A more complete understanding of cytokine dynamics in individual cells in active pulmonary tuberculosis patients will provide further knowledge about immunopathogenesis and protective immunity in human tuberculosis. This should ultimately enhance development of preventive and therapeutic strategies against this enormously successful intracellular pathogen.

CD40 ligand trimer enhances the response of CD8+ T cells to Mycobacterium tuberculosis

We investigated the effect of recombinant CD40 ligand trimer (CD40LT) on the functional capacity of peripheral blood CD8(+) T cells from healthy tuberculin reactors that were cultured with Mycobacterium tuberculosis-infected autologous monocytes. CD40LT enhanced the capacity of M. tuberculosis-responsive CD8(+) T cells to produce IFN-gamma by increasing the number of IFN-gamma-producing CD8(+) T cells and the amount of IFN-gamma produced per cell. CD40LT-induced IFN-gamma production was dependent on production of IL-12 and IL-18, but did not require IL-15. CD40LT up-regulated expression of the transcription factors phosphorylated CREB and c-Jun, both of which have been previously shown to stimulate IFN-gamma mRNA transcription by binding to the IFN-gamma promoter. CD40LT also enhanced the capacity of CD8(+) T cells to lyse M. tuberculosis-infected monocytes, and increased CTL activity was associated with higher expression of perforin and granulysin, but not of Fas ligand. We conclude that CD40LT can enhance CD8(+) T cell effector function in response to M. tuberculosis.