Immunofluorescence studies for immunoglobulins and complement C3 in synovial joint membranes in psoriatic arthritis.

Synovial tissues from fifteen patients with psoriatic arthritis were investigated with direct immunofluorescence staining for immunoglobulins (IgG, IgA, and IgM) and from eigth patients for complement component C3. As control groups, there were synovial tissues from seven patients with seropositive rheumatoid arthritis and five patients with meniscal tears. In psoriatic arthritis, immunoglobulins were found in plasma cells in 93% of the cases, always with the presence of IgG (93%) but also with IgA (47%) and IgM (7%). C3 could not be demonstrated. In seropositive rheumatoid arthritis IgG was demonstrated in all patients (100%), often together with IgA (43%) and IgM (57%). C3 was found in all of these patients. In patients with meniscal tears neither immunoglobulins nor C3 could be found. The present findings indicate immunological activity in synovial membranes in psoriatic arthritis. The low amount of IgM and the lack of C3 suggest a difference compared to seropositive rheumatoid arthritis.