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.