ABSTRACT
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.
ABSTRACT
Background & objectives: CD4+ T cells are involved in abnormal inflammatory responses causing adverse effects to the body. Th17 cells play a major role in immune disorders and the exact mechanism by which CD4+ T cells regulate its effector Th1 and Th17 phenotype at chromatin level is not clearly understood. This study was aimed to understand the role of matrix associated region (MAR) binding protein SMAR1 (scaffold/matrix attachment region binding protein 1) in T cell differentiation during inflammatory and autoimmune condition using SMAR1 transgenic mice as model. Methods: Wild type (C57BL/6J) and SMAR1 transgenic mice were used for isolation of T cells and further identification of different T cell lineages, along with histological analysis. Further, we studied autoimmune and inflammatory diseases using chemically induced and T cell transfer model of colitis and rheumatoid arthritis to better understand the role of SMAR1 in immune responses. Results: SMAR1 transgenic mice were resistant to dextran sodium sulphate (DSS) induced colitis with decreased expression of Th1 and Th17 specific cytokines. Overexpression of SMAR1 repressed Th17 response by negatively regulating RORγt and IL-17 expression. Downregulation of SMAR1 upregulated signal transducer and activator of transcription 3 (pSTAT3) and IL-17 expression that caused generation of more proinflammatory Th1 and Th17 cells leading to inflammation and disease. Interpretation & conclusions: Our results show an important role of SMAR1 in regulating CD4+ T cell differentiation during inflammatory disorders via regulation of both Th1 and Th17 signaling pathways. This study reveals a critical role of SMAR1 in maintaining the proinflammatory immune responses by repressing Th1 and Th17 cell function and it gives the novel insight into immune regulatory mechanisms.