Adhesion molecule expression in experimental myositis

Experimental allergic myositis (EAM) in Lewis rats, induced with partially purified myosin, is regarded as a model of human polymyositis. To clarify the role of adhesion molecules in the pathogenesis of EAM in Lewis rats, we investigated intramysial expressions of the intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1, and the serum level of soluble ICAM-1 in EAM rats. All the EAM rat muscles had scattered inflammatory foci, as well as cell infiltration and necrosis, by week 4 after the initial immunization (i.e., day 0 after the last immunization). As compared with the control muscles, ICAM-1 and VCAM-1 were strongly expressed immunohistochemically in the endothelium of vessels in the endomysium and perimysium, and to lesser extents in the inflammatory infiltrates and on the sarcolemma of nonnecrotic muscle fibers adjacent to the inflammatory infiltrates or invaded muscle fibers. ICAM-1 in the muscle extracts and sera from EAM rats increased on each test day, as compared with extracts from the normal controls. The values peaked on day 0 after the last immunization, then gradually decreased with time. ICAM-1 elevations in the muscle extracts were correlated with the percent of sections that had inflammatory lesions (P = 0.032) and the histological scores (P = 0.005) on day 0, whereas there was no significance on days 3 and 7. These findings suggest that the adhesion molecules ICAM-1 and VCAM-1 increase in the early stage of EAM, and function in the initiation of the inflammatory process of myositis.