Fibroblasts in synovitis in rheumatoid arthritis but not in noninflammatory synovial tissue in meniscus lesions express the carboxyterminal domain of procollagen type I.

Synovial tissue (ST) sections from patients with rheumatoid arthritis (RA) and meniscus lesions were stained using monoclonal antibodies against the carboxyterminal domain of human type I procollagen (alpha-pC) in avidin-biotin-peroxidase complex (ABC) staining. This gave a good signal-noise ratio and identified some synovial B-type lining cells and stromal fibroblasts in inflammatory RA ST but not in noninflammatory ST from patients with meniscus lesions. The authors' findings provide immunohistochemical evidence that the local fibroblasts in inflammatory ST in RA are activated, probably as a result of various humoral mediators produced in situ (by inflammatory mononuclear cells) in RA but not in normal noninflammatory ST.