[IgA rheumatoid factors in ankylosing spondylitis].

151 cases of ankylosing spondylitis, arranged in clinical stages I-IV, were investigated by immunological methods (determination of HLA-B27, immunocomplexes: conglutinin-, Clq-assay; IgG-, IgM-, IgA-rheumatoid factors) and with regard to acute phase proteins (CRP, C3/C4, alpha 1-acid glycoprotein). IgA-rheumatoid factors were demonstrated as dependent upon the stage of the disease in 23-41% of cases and appeared in 20-23% of cases simultaneously with immunocomplexes. Immunocomplexes appeared in 20-23% of cases. With regard to investigations of acute phase proteins, sedimentation rate and CRP correlated best. The frequent appearance of IgA-rheumatoid factors allows a definition of ankylosing spondylitis as seronegative only as far as the determination of IgG- and IgM- rheumatoid factors is concerned.