Distribution of the NF-KB Complex in the Inflammatory Exudates Characterizing the Idiopathic Inflammatory Myopathies

The transcription factor nuclear factor-KB (NF-KB) is a ubiquitously expressed protein family that is considered crucial in autoimmunity. We describe NF-KB p50 and p65, and the inhibitor I-KBa in the inflammatory exudates characteristic for the different idiopathic inflammatory myopathies (IIM), that is, endomysial CD8+ cytotoxic T cells invading non-necrotic fibers in polymyositis (PM) and sporadic inclusion body myositis (sIBM), and the perimysial-perivascular CD20+ B cells and CD4+ T cells in dermatomyositis (DM). We also analyzed other inflammatory cells in the vicinity of active inflammation sites. Strikingly, actively invading CD4+ cells in PM and sIBM contained both p65 and p50, whereas I-KBa was absent. This could point to a high activation state in which these cells are capable of expressing a variety of inflammatory mediators, contributing to the degradation of non-necrotic fibers. Secondly, CD68+ macrophages in the infiltrates in all three IIM subtypes showed strong nuclear p50 and I-KBa staining. This may point to a role for p50 in counteracting inflammation, a reaction that could be enhanced by an upregulation of I-KBa as we observed with immunofluorescence. These results shed further light on the immunopathology of PM, sIBM and DM. CD4+ and CD68+ mononuclear cells may play a more prominent role than previously assumed.