Specific serum IgA-antibodies in chlamydial-induced arthritis.

: A cohort analytic study was performed to investigate serum IgA-class antibodies against Chlamydia in 24 patients with chlamydial-induced arthritis (CIA). IgA-class antibodies against chlamydial antigens were positive (titre greater than or equal to 1:16) in 23 of the 24 IgG-positive CIA-patients (96%) in contrast to 16 of 40 patients (40%) with other rheumatic diseases (ankylosing spondylitis n = 6; undifferentiated arthritis n = 11; rheumatoid arthritis n = 12; degenerative joint disease n = 11), also positive for IgG-class chlamydial antibodies. Both the presence of specific IgA-antibodies and their geometric mean titre (1:28 vs. 1:4) differed significantly (p less than 0.001) between the two groups.