Phenotypic profile of major synovial cell populations in longstanding psoriatic arthritis.

Monoclonal antibody investigations showed that the vast majority of cells infiltrating the synovial tissue of 8 patients with longstanding psoriatic arthritis stained for both mononuclear phagocyte and class II major histocompatibility (MHC) antigens and were therefore referred to as type I synoviocytes. A minor though consistent number of cells bore solely class II MHC antigens and were recognized as type II synoviocytes, a subpopulation that has been reported to be characteristically augmented in immune synovitides. In contrast, no immunophenotypically identifiable lymphoid cells were seen. It is suggested that type I and II synoviocytes represent the late phase of the phlogistic process and contribute to maintaining the tissue injury.