The Role Of RIG-â…  And Chemokine Receptors In The Immnopathogenesis Of Idiopathic Inflammatory Myopathies

Background:The idiopathic inflammatory myopathies (ⅡMs) are a group of acquired autoimmune diseases of skeletal muscle including three subtypes:dermatomyositis (DM), polymyositis (PM), and inclusion body myositis (IBM), of which DM and PM show higher incidence among Chinese patients. The accurate mechanism of ⅡMs has never been elucidated yet. For a long time, DM has been modeled as a microangiopathy in which autoantibodies directed against endothelium cause vascular injury leading to ischemic myofiber damage, while PM has been modeled as a disease in which myofibers are invaded by antigen-specific cytotoxic T cells. In the last decades, many studies suggested that interferon-Ⅰ (IFN-Ⅰ), also plays an important role in the pathogenesis of ⅡMs, and plasmacytoid dendritic cells (pDCs) are considered as the main source of intramuscular IFN-Ⅰ. The production of IFN-Ⅰ in pDCs is mainly mediated by retinoic acid-inducible gene Ⅰ (RIG-Ⅰ) receptors and Toll like receptors (TLRs). However, there is still few knowledge of by which mechanism IFN-Ⅰ is produced by intramuscular pDCs in ⅡMs.Many studies have focused on the role of TLRs in the immnopathogenesis of ⅡMs. The up-regulation of many kinds of TLRs have been observed in muscle tissues of ⅡMs. Nevertheless, the role of RIG-Ⅰ protein in the pathogenesis of ⅡMs remains unclear.Objective:To investigate the expression of retinoic acid-inducible gene I(RIG-Ⅰ) in the muscle tissues from patients with ⅡMs, and to speculate the possible role of RIG-Ⅰ in the immunopathogenesis of ⅡMs.Methods:This is a retrospective case-control study. Muscle biopsies were taken from 20 dermatomyositis(DM) and 20 polymyositis (PM) patients. Besides,4 facioscapulohumeral muscular dystrophy (FSHD), and 4 non-myopathic patients were taken as control group. All the biopsy specimens were processed with hematoxylin-eosin and immunohistochemical (Mouse anti human RIG-Ⅰ antibodies) staining. We also examined the co-localization of RIG-Ⅰ and CD303, which is the specific surface marker of plasmacytoid dendridic cells (pDCs), by means of double immunofluorescence staining. Western-blot was performed for quantitative analysis.Results:Using immunohistochemistry study, there was strong expression of RIG-Ⅰ protein in DM/PM muscle tissues while in normal controls was virtually absent. RIG-Ⅰ was specifically expressed in inflammatory cells and vessel endothelium, and nonspecifically expressed in regenerating and necrotic fibers. Besides, strong positive expression was observed in the perimysial perifascicular fibers of DM. In FSHD muscle tissues, only a few regenerating and necrotic fibers was stained weakly and nonspecifically for RIG-Ⅰ. However, co-expression of RIG-Ⅰ and CD303 was not detected in DM/PM muscles. By western blot, the expression level of RIG-Ⅰ observed in DM and PM extracts was significantly higher than in control group (including Normal and FSHD groups (p<0.05))Conclusions:The expression of RIG-Ⅰ was signigicantly increased in DM/PM muscle tissues compared to controls. Based on the expression and function of RIG-Ⅰ. we speculated that RIG-Ⅰ may operate as a mediator in Th1 cytokine-induced chemokine expression. But RIG-Ⅰ may not play a major role in innate immune reaction mediated by type Ⅰ interferon.Background:Dermatomyositis(DM) is a systematic inflammatory diwase belonging thidiopathic inflammatory myopathies(IIMs). To date, the immunopathogenesis of DM has not bee打 definkely elucidated. For a lo打g time,DM has bee打 modeled as an autoimmune disease in which autoantibodies directed gainst edoeliuni cause vascular injury leading th ischemic myofiber damage. In the last decades, many studies suggested that interferon-1(IFN-1) also plays an important role in the pathogenesis of DM. The abnormal accumulation of pDCs in perimysium and endomysium is considered th be a primary intramuscular source of IFN-1 i DM.Studies of systemic lupus erythematosus(SLE) suggested that pDCs in peripheral blood may be activated and recruited to issues under SLE condition. And various chemokine receptors and their corresponding ligands were considered to play a important role i the maturity a打d migratio of pDCs. However,the role of CXCR3, CXCR4 and CCR7 involved in the recruitment of intramuscular pDCs in DM needs further investigation.Objective:To explore 1;he possle mechanism implicated in l:he Kcruitmet of pDCs byinvestigating the expression of CXCR3, CXCR4, and CCR7 0 itramuscular and circulating pDCs from DM patients.Methods:Immunohistochemistry and Westem-blot were used detect the :pision of CXCR3, CXCR4 and CCR7 in muscle biopsies. Co-localization of CD123+pDCs whh theth chemokine th)1 was forth examied by double immunofluorescence staining. Flow cytometry was used for investigating the proportion of pDCs in total PBMCs and the expression of CXCR3, CXCR4 and CCR7 on circulating pDCs,Results;CXCR3> CXCR4 and CCR7 were identified mainly expressing in infiltrating immune cells and large vessels i DM and polymyositis(PM) muscle tissues. CXCR4and CCR7, however, were also expressed in intramuscular blood vessels of nonthase controls. Westem-blot analysis showed marked up-regulation of expthssio of CXCR3, CXCR4 and CCR7 in muscle homogenate from patients with DM/PM as compared with that in normal controls. Immunofluorescence double-labelling with CD 123 and CXCR3/CXCR4/CCR7 antibothes showed 1:hat there were extensive co-localizatio of CD123 with CXCR3/CXCR4/CCR7. Flow cytometry showed a signicant decease i the proportion of CD 123+CD303+pDCs m total PBMCs from DM patients compared th PM and normal controls. Significantly increased expression of CXCR3, but not CXCR4 and CCR7, was identified by 幻ow cytometry in circulating pDCs in DM.Conclusions:Chemokine receptcws, CXCR3, CXCR4 and CCR7 play important role in the recruitment of pDCs from peripheral blood to muscle tissues. The exact influence of these chemokie receptois on the recruitment of pDCs,however,may vary.