OX40-OX40L expression in idiopathic inflammatory myopathies

To examine whether both OX40 and its ligand OX40L are expressed in idiopathic inflammatory myopathies and to investigate the types of inflammatory cells expressing OX40L.

Immunohistochemistry was performed in limb muscle specimens from dermatomyositis, polymyositis and inclusion body myositis patients to analyze the expression of OX40 and its ligand OX40L. Double immunofluorescence labeling was performed to clarify the phenotype of inflammatory cells expressing OX40L.

OX40 and OX40L expressing cells were observed in all subsets of inflammatory myopathies following a similar pattern of distribution mainly in the perimysium. In polymyositis and inclusion body myositis inflammatory cells expressing the receptors invaded non-necrotic muscle fibers. OX40L expression was also found in endothelial blood cells in all dermatomyositis and some polymyositis specimens. In all subsets of inflammatory myopathies OX40L was expressed by T cells (CD4+ and CD8+), macrophages (CD68+), B cells (CD20+) and myeloid dendritic cells (BDCA1+). Plasmacytoid dendritic cells (BDCA2+) expressing OX40L were found only in dermatomyositis and polymyositis.

The simultaneous expression of both OX40 and its ligand OX40L in idiopathic inflammatory myopathies suggests that they might participate in disease pathogenesis. Expression of OX40L by different types of cells within the inflamed muscle implies that OX40-OX40L interaction may contribute in disease mechanisms through different pathways.