| BackgroundDermatomyositis (DM) belongs to the idiopathic inflammatory myopathies (IIMs), which are characterized by subacute onset of symmetric proximal muscle weakness, specific skin involvement, inflammatory infiltrates within the muscle, and pathologically perifascicular atrophy. To date, the immunopathogenesis of DM has not been fully clarified.More recently, much attention has been focused on type Ⅰ interferon (IFN), because of its potential role in IIM, as well as in other autoimmune diseases, such as systemic lupus erythematosus (SLE) and Sjogren’s syndrome. Plasmacytoid dendritic cells (pDCs), a type of natural IFN-I-producing cell, are also detected in the perimysium and endomysium of DM muscle. IFN-I was mainly product by exogenous and endogenous active pathway. The exogenous way is triggered by viral infection and nucleic acid in virus was recognized by the specific Toll-like receptors (TLRs). The endogenous active pathway induces IFN-I through activation of retinoic acid inducible gene I (RIG-I) which detects immune complexes of nucleic acid and protein. TLRs and RIG-I are the major receptors in the IFN-I system, whether they play the role in muscle tissue of DM at the same time or what is the more preferential receptor and player in DM, and by which way the pDCs induce abundant IFN-I. These mechanisms have not been cleared. In our study, we explore the role of TLRs and RIG-I in endogenous production of type Ⅰ interferon in dermatomyositis.Part Ⅰ:The pathological characteristics of dendritic cells in muscle tissue of idiopathic inflammatory myopathyObjective:To study the pathological characteristics of dendritic cells in muscle tissue of DM, polymyositis (PM) and inclusion body myositis (IBM), and to preliminarily discuss the function of the myeloid dendritic cell (mDCs) and pDCs in the immunopathogenesis of IIM.MethodMuscle biopsies were taken from 27 IIM patients, including 10 DM patients,10 PM,4 IBM and 3 non-myopathic patients, taken as control group. We summarized the clinical data and pathological characteristics in 27 IIM patients. All the biopsy specimens were processed with hematoxylin-eosin and immunohistochemical staining for anti-BDCA-1 and anti-BDCA-2.ResultThe expression of mDCs was significantly positive in perivasculitis and inflammatory infiltrationn of mDCsM and IBM patients. The pDCs was expressed significantly in DM (8/10), but not in PM and IBM. The location of pDC is in fascia, endomysium and perimysium. There was no expression of the mDCs and the pDCs in non-myopathic patients.ConclusionDendritic cells may be implicated in the immunopathogenesis of IIM by infiltration in inflammation and damage in muscle fiber. The specific expression of pDCs in DM suggests that pDCs are closely related with immune characteristic pathology in DM.Part Ⅱ:Role of Toll-like receptors and retinoic acid inducible gene I in the immunopathogenesis of dermatomyositisObjectiveTo inveatigate the pathological characteristics of RIG-I and Toll-like receptors including TLR-3, TLR-4, TLR-7 and TLR-9 in muscle tissue of dermatomyositis (DM), and to speculate the possible role of RIG-I and TLRs in the DM.MethodMuscle specimens were obtained retrospectively from 20 DM patients and 11 controls, of whom,4 had polymyositis (PM),4 had facioscapulohumeral muscular dystrophy (FSHD), and 3 non-myopathic patients. All the biopsy specimens were processed with hematoxylin-eosin and immunohistochemical staining for anti-TLR-3, anti-TLR-4, anti-TLR-7, anti-TLR-9 and anti-RIG-I.ResultImmunohistochemistry demonstrated that TLR-3 and RIG-I was expressed preferentially in the perimysial perifascicular fibers of DM tissues, but little in inflammatory infiltrates or in regenerating and necrotic fibers of DM and PM. In contrast, muscle biopsies from 4 FSHD and 3 non-disease controls showed negative TLR-3 and RIG-I staining. RIG-I was also expressed in the inflammatory infiltrates within the fascia of DM. TLR-4 and TLR-9 were expressed mainly in inflammatory infiltrates in DM, PM and FSHD. Three non-disease controls showed negative TLR-4 and TLR-9 staining. There was positive expression of TLR-9 in the inflammatory infiltrates within the fascia of DM. Expression of TLR-7 in inflammatory infiltrates was only found in 9 of 20 DM and a few PM patient, the non-disease controls showed negative TLR-7 staining in muscle sections. However, there was strong expression of TLR-7 in intramuscular nerve fibers in all DM patients and controls.By western blot, expression of TLR-3 and RIG-I in muscle from DM patients was increased significantly compared with that in the controls (p<0.05). TLR-9 had significantly higher expression in DM patients compared with the others (p<0.05). There was no significant difference among DM, PM and FSHD patients for TLR-4 expression (p>0.05), however, compared with the no-disease controls, TLR-4 expression in DM was significant (p<0.05). There were no visible bands in the no-disease controls, FSHD and PM patients, while the expression of TLR-7 was marked in the muscle homogenate from patients with DM (p<0.05).ConclusionTLR-3 and RIG-I, which is expressed preferentially in perifascicular atrophy fibers, may be implicated in the formation of perifascicular atrophy in DM. TLR-9 was expressed significantly in the muscle tissue of DM and may play the important role in the immunopathogenesis of DM.Part Ⅲ:Role of Toll-like receptors and retinoic acid inducible gene I in endogenous production of type Ⅰ interferon in dermatomyositisObjectiveTo demonstrate the mechanism of endogenous production of type I interferon in DM by the co-expression of pDCs with TLRs and RIG-IMethodMuscle specimens were obtained retrospectively from 20 DM patients and 11 controls; of whom,4 had PM,4 had FSHD, and 3 non-myopathic patients. All the biopsy specimens were processed with immunofluorescence staining for anti-TLR-3, anti-TLR-4, anti-TLR-7, anti-TLR-9 and anti-RIG-I. And we detect the co-expression of pDCs with TLRs and RIG-I by the immunofluorescence double staining.ResultImmunofluorescence demonstrated that TLR-3 and RIG-I was expressed preferentially in the perimysial perifascicular fibers of DM tissues, but little in inflammatory infiltrates or in regenerating and necrotic fibers of DM and PM. In contrast, muscle biopsies from 4 FSHD and 3 non-disease controls showed negative TLR-3 and RIG-I staining. TLR-4 and TLR-9 were expressed mainly in inflammatory infiltrates in DM, PM and FSHD. Three non-disease controls showed negative TLR-4 and TLR-9 staining. Expression of TLR-7 in inflammatory infiltrates was only found in 9 of 20 DM and a few PM patient, the non-disease controls showed negative TLR-7 staining in muscle sections. However, there was strong expression of TLR-7 in intramuscular nerve fibers in all DM patients and controls. There was positive expression of TLR-9 and RIG-I in the inflammatory infiltrates within the fascia of DM.TLR-9 was mainly observed in inflammatory infiltrates, and pDCs producing the TLR-9 within the endomysium, perimysium and fascia. Within the endomysium of DM, some pDCs displayed double immunofluorescence of TLR-7. Although RIG-I shared similar presentation with TLR-3 in DM, there was no coexpression of BDCA-2+ pDCs with RIG-I and TLR-3 identified, as well as TLR-4.ConclusionThe endogenous production of type Ⅰ IFN in DM may be generated by pDCs, mainly through the TLR-9 pathway, although TLR-7-mediated type Ⅰ IFN production may also be present. TLR-3 and RIG-I, which is expressed preferentially in perifascicular atrophy fibers, may be implicated in the formation of perifascicular atrophy in DM. |
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