Abstract

Analysis of five serum samples and three synovial fluids from patients with ankylosing spondylitis (AS) and five serum samples from healthy blood donors for the presence of antibodies cross reacting with the Fc part of rabbit IgG (rheumatoid factors (RFs] using an isotype specific, enzyme linked immunosorbent assay (ELISA) showed only insignificant amounts of free RFs, while IgG RFs were observed in alkaline dissociated circulating immune complexes (CICs). Only insignificant amounts of free antibodies reacting with the psoriasis associated antigen pso p27 could be detected in the samples, while extensive amounts of IgG antibodies and moderate amounts of IgM antibodies reacting with pso p27 were detected in alkaline dissociated CICs from the patients. Pso p27 has been reported to share a common determinant with the Fc part of human IgG. Removal of the RF activity from the CICs of patients with AS by absorption with IgG resulted in a decrease of the anti-pso p27 activity. Monoclonal anti-pso p27 antibodies in a sandwich ELISA were used to detect antigens cross reacting with pso p27. A positive reaction was observed in all serum CICs and in one of the synovial fluid CICs. The data indicate that antigens related to pso p27 participate in CIC formation in AS and may also be responsible for the elicitation of rheumatoid factors in patients with AS.