Distribution of immunoglobulin classes in plasma cells in various kinds of synovitis

Sixty-five cases of synovitis corresponding to eight groups (seropositive and seronegative rheumatoid arthritis (RA), ankylosing spondylitis, psoriatic arthritis, post-traumatic arthritis, osteoarthritis, osteonecrosis and unclassified synovitis) were investigated in specimens stored as paraffin blocks. Immunoglobulin class content (heavy chains: G, A, M and their associated light chains: K, L) of the plasma cells was determined by the immunoperoxidase method. Plasma cells were observed in all cases in both RA groups but not in all cases of the other groups. All three classes of immunoglobulins were observed. The proportion of IgM cells was numerically larger in seropositive rheumatoid arthritis than in seronegative RA. However, due to the great case-to-case dispersion and small group size, this difference was not significant. A routine investigation of intracellular immunoglobulins cannot, therefore--at least with present knowledge--contribute to the diagnosis or prognosis of a given case of synovitis.