Defective Antigen Presentation Leads to Upregulation of PD1 and IL-10 in HIV-TB Co-Infection.

Human immunodeficiency virus-tuberculosis (HIV-TB) co-infection poses a challenge to the immunologists in developing new diagnostic and therapeutic tools. Mechanisms behind the breakdown of the immune defense of the co-infected individual are poorly known. Numerous studies in HIV alone have revealed the role of PD1, TAP, and IL-10, but not in co-infection. The interaction of the 2 distinct bugs, which is resulting in domination over the host immune system, is still a lacuna. Hence, we aimed to portray functions of IL-10, TAP, and PD1 molecules in HIV-TB co-infection. Co-culture cells challenged with γ-irradiated M.Tb under various conditions resulted in high interleukin (IL)-10 secretion and high percentage of PD1 expression on CD8 T cells, which might be due to defective antigen presentation of TAP on dendritic cells and macrophages. Herein our observations provide an insight into the escape mechanisms by M.Tb in HIV-infected individuals from the host immune responses leading to TB co-infection.

Down regulation of RANTES in pleural site is associated with inhibition of antigen specific response in tuberculosis.

Tuberculosis is the most common infectious reason for death and a major cause of pleural effusion globally. To understand the role of chemokines in trafficking of cells during TB pleurisy, we studied the responses to MTB, Ag85A in cells from pleural fluids and peripheral blood. Patients with TB pleural effusions, malignant effusions and asymptomatic healthy controls were enrolled. High expression (p < 0.05) of IP-10, MCP-1, MIG, IL-8, IFN-γ and IL-23 were observed in pleural fluids of TB patients compared to their plasma where expression of RANTES was significantly higher (p < 0.05). On specific stimulation of PFMCs with Ag85A, expression of RANTES was significantly lower in TB compared to NTB patients. We also observed increased expression of T regs and PD1 on CD8+T cells in PFMC of TB patients. Though some of the inflammatory chemokine/cytokines were up-regulated in pleura of TB patients, antigenic stimulation failed to induce them indicating poor antigenic responses at the site. Low expression of RANTES might be a reason for decreased trafficking of cells to the site and dissemination of infection into pleural site. The pattern of RANTES expression in pleural fluid vs serum is interesting. The observations necessitate further studies to investigate the levels of RANTES for its potential biological relevance in TB immunity and its use as a biomarker for diagnosis of pleural TB.

Mycobacterial r32-kDa antigen-specific T-cell responses correlate with successful treatment and a heightened anti-microbial response in human leprosy patients.

BACKGROUND: Immunological characterization of mycobacterial peptides may help not only in the preparation of a vaccine for leprosy but also in developing in vitro T-cell assays that could perhaps be used as an in vitro correlate for treatment outcome. The main goal of this study was to evaluate the use of Mycobacterium bovis recombinant 32-kDa protein (r32-kDa) antigen-stimulated T-cell assay as a surrogate marker for treatment outcome and monitor vitamin D receptor (VDR)-mediated anti-microbial responses during multidrug therapy (MDT) in leprosy. METHODS: Newly diagnosed tuberculoid and lepromatous leprosy patients were enrolled and followed up during their course of MDT at 6 and 12 months. IFN-γ, IL-10, IL-17 and IL-23 levels in culture supernatants and expression of VDR, TLR2, LL37 and DEFB in r32-kDa-stimulated PBMCs were measured. Controls comprised household contacts (HHCs) and healthy endemic subjects (HCs). RESULTS: Significant differences were observed in the levels of IFN-γ, IL-17, IL-23, VDR and anti-microbial peptides LL37 and DEFB after treatment and when compared with that of HHCs and HCs, respectively. CONCLUSIONS: These findings suggest that responses to r32-kDa antigen reflect an improved immunological and anti-microbial response in leprosy patients during therapy, thereby indicating its potential use as an immune correlate in the treatment of leprosy patients.

Association of Taq I, Fok I and Apa I polymorphisms in Vitamin D Receptor (VDR) gene with leprosy.

BACKGROUND: Vitamin D Receptor (VDR) is a transacting transcription factor which mediates immunomodulatory function and plays a key role in innate and adaptive immune responses through its ligand and polymorphisms in VDR gene may affect its regulatory function. OBJECTIVE: To investigate the association of three VDR gene polymorphisms (TaqI rs731236, FokI rs2228570 and ApaI rs7975232) with leprosy. METHODS: The study group includes 404 participants of which 222 were leprosy patients (paucibacillary=87, multibacillary=135) and 182 healthy controls. Genotyping was done using PCR-RFLP technique. Statistical analysis was performed using SNP Stats and PLINK software. RESULTS: The VDR FokI (rs2228570) ff genotype, ApaI (rs7975232) AA, Aa genotype and haplotype T-f-a, T-F-A were positively associated with leprosy when compared to healthy controls. CONCLUSION: The two variants at Fok and Apa positions in VDR gene are significantly associated with leprosy. Genotypes at FokI (ff), ApaI (aa) and haplotype (T-F-a, T-f-a) may contribute to the risk of developing leprosy by altering VDR phenotype/levels subsequently modulation of immune response.

Genetic association of G896A polymorphism of TLR4 gene in leprosy through family-based and case-control study designs.

BACKGROUND: Polymorphisms in TLR4 may change the function of the protein and alter the efficiency of immune response of host to infection. The high relevance of host gene polymorphisms with outcome of Mycobacterium leprae infection led us to study the genetic association of TLR4 G896A polymorphism in order to identify its risk among contacts of affected leprosy patients. METHODS: For case-control study design a total of 628 individuals were recruited; 17 multicase leprosy families which included 32 case-parent trios were considered for family-based study. Genotyping was done using PCR-RFLP method. RESULTS: In case-control study AA genotype was positively associated while GA genotype was negatively associated with leprosy. In family based transmission disequilibrium test (TDT) analysis allele G was found to be over transmitted to the affected individuals. CONCLUSION: Case-control study suggests that homozygous AA genotype may confer susceptibility and heterozygous GA genotype may confer resistance to leprosy, while allele A was observed to increase risk and that of allele G may confer resistance to leprosy. No strong transmission disequilibrium was detected in family-based TDT analysis, possibly due to lower number of trios. In contrast to case-control data allele G was over transmitted to the affected ones in TDT analysis. To conclude, the frequencies of genotypes in household contacts were almost the same as in leprosy patients, suggesting that contacts with AA genotype may be at higher risk of leprosy and may therefore require prophylactic inputs.

Killer cell immunoglobulin like receptor gene association with tuberculosis.

NK cells are vital components of innate immune system and are the first cells which come into picture mediating resistance against intracellular pathogens. NK cell cytotoxicity is modulated by a wide variety of cell surface receptors that recognize and respond towards infected cells. Activation of NK cells are controlled by both inhibitory and activating receptors, encoded by KIR genes and bind to HLA ligands. Not much is known about KIR genes and their influence on the pathogenesis with M. tuberculosis infection. Our study aimed at detecting the presence of 14 KIR genes, their distribution and their association with tuberculosis. Total 77 different genotype combinations were observed which belonged to B-haplotype. Fifteen genotypes were similar to those reported in other world populations while remaining 62 were unique to this study group. Inhibitory genes KIR3DL1, KIR2DL3 and activating genes KIR2DS1, KIR2DS5 conferred susceptibility towards TB either individually or in haplotype combinations. The complimentary MHC ligands need to be tested for the functional relevance of the associated genes.

IL-10 high producing genotype predisposes HIV infected individuals to TB infection.

Interleukin (IL-10), an anti-inflammatory cytokine, is known to have dual effect on the host immune system. One of these roles is that it provides an effective autoregulatory mechanism which protects the host from excessive inflammation and tissue damage which is in part initiated by the Th1 driven pro-inflammatory immune responses during infections (such as TB, HIV and malaria). However, though beneficial, this autoregulatory mechanism is at times exploited by pathogens which evade elimination by Th1 driven immune response leading to chronic infections. The main aim of this study therefore was to study the influence of IL-10 polymorphism in relation to its levels with respect to HIV-TB co-infection. A total of 452 participants were categorized into HIV (121), active tuberculosis (TB) (118), HIV-TB (HT) (106) groups and healthy control group (107). Polymorphism for IL-10 gene (positions -1082, -819, -592) was studied using ARMS-PCR, RFLP. IL-10 and IFN-γ levels in antigen stimulated cultures were measured using ELISA. Statistical analysis was performed using Chi-Square (χ(2)) test, One-way ANOVA and t-tests. IL-10 (-1082) GG genotype was positively associated with HIV-TB, whereas AG with HIV and AA with TB. The cohort with GG genotype also had significantly high stimulated levels of IL-10 compared to AG and AA. AC genotype was significantly frequent in HIV-TB group at IL-10 (-592) position when compared with controls. HIV positive individuals with GG genotype at IL-10 (-1082) position and high IL-10 levels may have a high risk of developing TB co-infection.

Vaccine for tuberculosis: up-regulation of IL-15 by Ag85A and not by ESAT-6.

IFN-γ is the most commonly measured cytokine released by the cells to define the cellular immune responses induced by the vaccine candidates for tuberculosis. IL-15 acts as a co-stimulator in IFN-γ production by NK cells and may therefore be important in the control of Mycobacterium tuberculosis that requires IFN-γ for clearance. The aim of the study is to determine whether Ag85A can also stimulate the innate immune response through the expression of IL-15, a cytokine that bridges the innate and adaptive immune systems. The expression of IL-15 was up regulated by about 4 fold in PPD+ healthy controls as compared with TB patients. Significantly higher expression of IL-15 mRNA in the Ag85A stimulated cells not only in PPD+ healthy controls but also in TB patients substantiates the use of Ag85A as a vaccine candidate over ESAT-6.