Sambasivan Venkatasubramanian

Interleukin 22 Inhibits Intracellular Growth of Mycobacterium tuberculosis by Enhancing Calgranulin A Expression

Previously, we found that interleukin 22 (IL-22) inhibits intracellular growth of Mycobacterium tuberculosis in human monocyte-derived macrophages (MDMs). In the current study, we determined the mechanisms underlying these effects. We found that W7, a phagolysosomal fusion inhibitor, abrogates IL-22-dependent M. tuberculosis growth inhibition in MDMs, suggesting that IL-22 acts through enhanced phagolysosomal fusion. Our microarray analysis indicated that recombinant IL-22 (rIL-22) enhances the expression of an intracellular signaling molecule, calgranulin A. This was confirmed by real-time polymerase chain reaction, Western blot, and confocal microscopy. Calgranulin A small interfering RNA (siRNA) abrogated rIL-22-dependent growth inhibition of M. tuberculosis in MDMs. IL-22 enhanced Rab7 expression and downregulated Rab14 expression of M. tuberculosis-infected MDMs, and these effects were reversed by calgranulin A siRNA. These results suggest that M. tuberculosis growth inhibition by IL-22 depends on calgranulin A and enhanced phagolysosomal fusion, which is associated with increased Rab7 and reduced Rab14 expression.

IL-21-dependent expansion of memory-like NK cells enhances protective immune responses against Mycobacterium tuberculosis.

Natural killer (NK) cells are traditionally considered as innate cells, but recent studies suggest that NK cells can distinguish antigens, and that memory NK cells expand and protect against viral pathogens. Limited information is available about the mechanisms involved in memory-like NK cell expansion, and their role in bacterial infections and vaccine-induced protective immune responses. In the current study, using a mouse model of tuberculosis (TB) infection, we found that interferon-gamma producing CD3−NKp46+CD27+KLRG1+ memory-like NK cells develop during Bacille Calmette–Guérin vaccination, expand, and provide protection against challenge with Mycobacterium tuberculosis (M. tb). Using antibodies, short interfering RNA and gene-deleted mice, we found that expansion of memory-like NK cells depends on interleukin 21 (IL-21). NKp46+CD27+KLRG1+ NK cells expanded in healthy individuals with latent TB infection in an IL-21-dependent manner. Our study provides first evidence that memory-like NK cells survive long term, expansion depends on IL-21, and involved in vaccine-induced protective immunity against a bacterial pathogen.

Association of Interleukin-10 Gene Promoter Polymorphism in Allergic Patients

AIM Allergic diseases are increasing alarmingly worldwide affecting >30% of the population, including India. Allergy is the result of interaction of the epitopes on the protein with the immunoglobulin E (IgE). T helper cell-2 cytokines promote allergen-specific IgE antibody and induce eosinophil-dominated inflammatory tissue responses. Interleukin-10 (IL-10), an antiinflammatory cytokine, plays a major role in the development of the allergy. The cytokine gene polymorphism of -592C→A (rs1800872) and -1082G→A (rs1800896) of IL-10 may influence the expression of the protein. Hence, the current study was aimed to evaluate the persistent association between these variants in the susceptibility of the disease. METHODS The allelic and genotype frequencies corresponding to IL-10 (-592C→A; -1082G→A) were determined in 94 allergic patients and 100 controls. Genomic typing was performed with polymerase chain reaction with sequence-specific primers. RESULT The genotype AA at -592 position (p<0.000; odds ratio [OR] 9.92; 95% confidence interval [CI]=5.06-19.42) and GG at IL-10-1082 position (p<0.04; OR=2.47; 95% CI=1.003-4.96) was associated significantly in patients compared with controls. A considerable frequency of A-A haplotype in the patients and C-A, C-G haplotypes in controls was observed. A highly noteworthy difference was found in diplotype frequencies of A/A-A/A and A/A-G/A in patients and A/C-G/G and A/C-G/A in the controls. CONCLUSION Our results indicate that haplotype and diplotype frequencies of the IL-10 locus may confer susceptibility to allergic patients.

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.

Tissue factor expression by myeloid cells contributes to protective immune response against Mycobacterium tuberculosis infection

Tissue factor (TF) is a transmembrane glycoprotein that plays an essential role in hemostasis by activating coagulation. TF is also expressed by monocytes/macrophages as part of the innate immune response to infections. In the current study, we determined the role of TF expressed by myeloid cells during Mycobacterium tuberculosis (M. tb) infection by using mice lacking the TF gene in myeloid cells (TFΔ) and human monocyte derived macrophages (MDMs). We found that during M. tb infection, a deficiency of TF in myeloid cells was associated with reduced inducible nitric oxide synthase (iNOS) expression, enhanced arginase 1 (Arg1) expression, enhanced IL‐10 production and reduced apoptosis in infected macrophages, which augmented M. tb growth. Our results demonstrate that a deficiency of TF in myeloid cells promotes M2‐like phenotype in M .tb infected macrophages. A deficiency in TF expression by myeloid cells was also associated with reduced fibrin deposition and increased matrix metalloproteases (MMP)‐2 and MMP‐9 mediated inflammation in M. tb infected lungs. Our studies demonstrate that TF expressed by myeloid cells has newly recognized abilities to polarize macrophages and to regulate M. tb growth.

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.

NK-CD11c+ Cell Crosstalk in Diabetes Enhances IL-6-Mediated Inflammation during Mycobacterium tuberculosis Infection

In this study, we developed a mouse model of type 2 diabetes mellitus (T2DM) using streptozotocin and nicotinamide and identified factors that increase susceptibility of T2DM mice to infection by Mycobacterium tuberculosis (Mtb). All Mtb-infected T2DM mice and 40% of uninfected T2DM mice died within 10 months, whereas all control mice survived. In Mtb-infected mice, T2DM increased the bacterial burden and pro- and anti-inflammatory cytokine and chemokine production in the lungs relative to those in uninfected T2DM mice and infected control mice. Levels of IL-6 also increased. Anti-IL-6 monoclonal antibody treatment of Mtb-infected acute- and chronic-T2DM mice increased survival (to 100%) and reduced pro- and anti-inflammatory cytokine expression. CD11c+ cells were the major source of IL-6 in Mtb-infected T2DM mice. Pulmonary natural killer (NK) cells in Mtb-infected T2DM mice further increased IL-6 production by autologous CD11c+ cells through their activating receptors. Anti-NK1.1 antibody treatment of Mtb-infected acute-T2DM mice increased survival and reduced pro- and anti-inflammatory cytokine expression. Furthermore, IL-6 increased inflammatory cytokine production by T lymphocytes in pulmonary tuberculosis patients with T2DM. Overall, the results suggest that NK-CD11c+ cell interactions increase IL-6 production, which in turn drives the pathological immune response and mortality associated with Mtb infection in diabetic mice.

A TLR9 agonist promotes IL-22-dependent pancreatic islet allograft survival in type 1 diabetic mice

Pancreatic islet transplantation is a promising potential cure for type 1 diabetes (T1D). Islet allografts can survive long term in the liver parenchyma. Here we show that liver NK1.1+ cells induce allograft tolerance in a T1D mouse model. The tolerogenic effects of NK1.1+ cells are mediated through IL-22 production, which enhances allograft survival and increases insulin secretion. Increased expression of NKG2A by liver NK1.1+ cells in islet allograft-transplanted mice is involved in the production of IL-22 and in the reduced inflammatory response to allografts. Vaccination of T1D mice with a CpG oligonucleotide TLR9 agonist (ODN 1585) enhances expansion of IL-22-producing CD3-NK1.1+ cells in the liver and prolongs allograft survival. Our study identifies a role for liver NK1.1+ cells, IL-22 and CpG oligonucleotides in the induction of tolerance to islet allografts in the liver parenchyma.

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.

Alcohol enhances type 1 interferon-α production and mortality in young mice infected with Mycobacterium tuberculosis

In the current study, we used a mouse model and human blood samples to determine the effects of chronic alcohol consumption on immune responses during Mycobacterium tuberculosis (Mtb) infection. Alcohol increased the mortality of young mice but not old mice with Mtb infection. CD11b+Ly6G+ cells are the major source of IFN-α in the lungs of Mtb-infected alcohol-fed young mice, and IFN-α enhances macrophage necroptosis in the lungs. Treatment with an anti-IFNAR-1 antibody enhanced the survival of Mtb-infected alcohol-fed young mice. In response to Mtb, peripheral blood mononuclear cells (PBMCs) from alcoholic young healthy individuals with latent tuberculosis infection (LTBI) produced significantly higher amounts of IFN-α than those from non-alcoholic young healthy LTBI+ individuals and alcoholic and non-alcoholic old healthy LTBI+ individuals. Our study demonstrates that alcohol enhances IFN-α production by CD11b+Ly6G+ cells in the lungs of young Mtb-infected mice, which leads to macrophage necroptosis and increased mortality. Our findings also suggest that young alcoholic LTBI+ individuals have a higher risk of developing active TB infection.