Complement in acute and chronic arthritides: Assessment of C3c, C9, and protectin (CD59) in synovial membrane

Objectives-To investigate the role of complement cascade induced damage and protection against it in acute arthritides compared to rheumatoid arthritis and other chronic joint derangements. Methods-C3c, C9, and protectin (CD59) were examined by avidin-biotin-peroxidase complex staining. Results-Marked deposits of C3c and C9 were found in synovial vasculature and intercellular matrix of the lining in rheumatoid arthritis and in acute arthritides (including bacterial, reactive, and osteoarthritis flare up). Furthermore, protectin was not visible in synovial lining cells and was relatively weakly expressed in stromal and endothelial cells in rheumatoid arthritis; also in acute arthritides protectin expression was weak. In contrast, C3c and C9 deposits were not found in chronic conditions associated with degenerative diseases (osteoarthritis and osteochondritis dissecans) or mechanical causes (patellar luxation and a ruptured meniscus), in which also the protectin expression was prominent in synovial lining, endothelial and some stromal cells. Conclusions-Activation of the complement in rheumatoid arthritis and in acute arthritides seems to be associated with a decreased protection of synovial cells against cellular effects and lysis mediated by membrane attack complex.