Studies of circulating immune complexes in ankylosing spondylitis.

Circulating immune complexes (CIC) were sought, by a fluorescent antibody immunophagocytosis (FIP) assay, in the sera of 30 patients with ankylosing spondylitis (AS), 62 with rheumatoid arthritis (RA), 27 with systemic lupus erythematosus (SLE) and 67 normal controls. Component analysis of CIC revealed significant elevations of total immunoglobulin (TIg), IgM and C3 for all patient study groups. In contrast to RA and SLE, CIC in AS sera contained significantly increased IgA and decreased IgG components. Categorization of AS patients as Grade I (mild disease) or Grade II (moderate/advanced disease) revealed no significant differences between the 2 groups in mean serum levels, component composition or prevalence of CIC. These results confirm the occurrence of CIC in AS but do not clarify the pathogenetic influence, if any, of CIC in this disease.