The nonnecrotic invaded muscle fibers of polymyositis and sporadic inclusion body myositis: on the interplay of chemokines and stress proteins.

Although polymyositis (PM) and sporadic inclusion body myositis (IBM) represent distinct disease entities, both are associated with the autoimmune destruction of muscle fibers. We investigated the pro-inflammatory mechanisms around the nonnecrotic invaded muscle fiber, comparing between PM and IBM. The expression and distribution of chemokines, inducible NO synthase (iNOS), and heat shock proteins (HSP) was studied in detail, using immunofluorescence, and western blotting. Important upregulation of the cytotoxic tandem HSP90/iNOS and the chemokines: IFNγ inducible protein of 10kd, stromal cell-derived factor and monocyte chemoattractant protein 1, were observed in the actively invading inflammatory cells. From our results, we propose a model in which the joint action of chemokines and cytotoxic factors in cytotoxic T-cells, macrophages and myeloid dendritic cells invading the myofiber, ultimately leads to its demise. The processes described seem to be universal to PM and IBM alike. Our observations further consolidate the important autoimmune component of IBM, a feature still under debate within the scientific community.