RESUMO
OBJECTIVE: To assess the presence of CD59 and the deposition of membrane attack complex (MAC) of complement system in skeletal muscle from patients with juvenile dermatomyositis (JDM), in comparison to patients with muscular dystrophies (MD) and children with normal muscle biopsies. METHODS: Muscle specimens obtained for diagnostic purposes from 10 patients with JDM, 6 with MD, and 7 children whose biopsies showed normal histology were analyzed. Immunohistological staining was performed using Mab against CD59 (YTH 53.1) and MAC (WU 7.2). RESULTS: Immunohistochemical staining for CD59 was weak and irregularly distributed on muscle fibers of all patients with JDM. Two of the 9 biopsies that allowed analysis of vessels showed negative CD59 staining in all vessels; in the remaining 7 patients, there was weak staining in a proportion of the vessels. In contrast, uniform and strong or moderate immunoreactivity was detected on the sarcolemma and in intramuscular endothelium in all normal and MD samples. Immunostaining for MAC was strong in JDM muscle vessels, and weak in normal or MD muscle. An inverse relation was found between MAC deposition and presence of CD59 in vessels in 6/9 JDM biopsies and in all normal and MD samples. CONCLUSION: Decreased CD59 expression in JDM muscle fibers and vessels may be associated with muscle lesions mediated by deposition of MAC of complement in JDM.