INTERLEUKIN-1 EXPRESSION IN INFLAMMATORY MYOPATHIES - EVIDENCE OF MARKED IMMUNOREACTIVITY IN SARCOID GRANULOMAS AND MUSCLE-FIBERS SHOWING ISCHEMIC AND REGENERATIVE CHANGES

The most frequent autoimmune adult inflammatory myopathies are dermato myositis, polymyositis, inclusion body myositis, and sarcoid myopathy. Interleukin-1 (IL-1) is a pleiotropic molecule, implicated in the inf lammatory process, but also in tissue protection and remodelling. We e valuated the immunocytochemical expression of IL-1 alpha and beta in f rozen muscle biopsy specimens from patients with dermatomyositis (15 c ases), polymyositis (five cases), inclusion body myositis (five cases) and sarcoid myopathy (five cases). Positive immunoreactivities, were observed in both inflammatory cells and muscle fibres. Specificity of the immunostaining was assessed by Western blot experiments. IL-1 posi tive inflammatory cells were rare in polymyositis and inclusion body m yositis, moderately abundant in dermatomyositis, and prominent in sarc oid myopathy granulomas. In sarcoid myopathy, 24.6 +/- 4.1% inflammato ry cells were IL-1 alpha positive and 45.2 +/- 2.6% were IL-1 beta-pos itive. IL-1 positive muscle fibres were mainly observed in dermatomyos itis, usually remote from inflammatory infiltrates. Positive immunosta ining for IL-1 was observed in fibres showing ischaemic punched-out va cuoles, that correspond to areas of myosinolysis, in atrophic perifasc icular fibres, and in fibres located within healing microinfarcts. All NCAM-positive regenerating fibres were IL-1 positive. We conclude tha t : (i) IL-1 is expressed in granulomas of sarcoid myopathy, which is in keeping with the role ascribed to IL-1 in the formation of granulom as; (ii) IL-1 is expressed by muscle fibres undergoing ischaemic damag e; and (iii) IL-1 expression by muscle fibres is associated with myofi brillar protein breakdown and regeneration.