Characterization of synovial macrophages by monoclonal antibodies in rheumatoid arthritis and osteoarthritis.

Inflamed synovium in rheumatoid arthritis (RA) and activated (inflammatory) osteoarthritis (aOA) sometimes demonstrates close similarities in routine histology. If the clinical findings are ambiguous, too, differentiation may become difficult, and the only diagnosis is "chronic unspecific synovitis". By immunohistologic staining with monoclonal antibodies of the Ki-M-series directed against cells of the monocyte/macrophage lineage semiquantitative evaluation of tissue samples is possible thus gaining helpful results for the differential diagnosis. There are significantly more macrophages in RA than in aOA especially in the synovial lining. Proliferating and activation markers also show slight but significant augmentation (OKT9) in RA.