Chlamydia trachomatis serology in ankylosing spondylitis.

Demonstration of chlamydial antibodies in patients with ankylosing spondylitis (AS) could show an etiological roel of Chlamydia trachomatis in this condition. We studied serum specimens from 50 HLA-B27 positive patients with AS (Group I), 34 HLA-B27 positive patients with other rheumatic diseases (Group II), 67 HLA-B27 positive healthy blood donors (Group III) and 37 healthy untyped blood donors. (Group IV). Measured by an immunoperoxidase assay (IPA) chlamydial IgA (titre ≥1∶20) was more prevalent in the HLA-B27 positive persons than in the healthy controls not selected for HLA-group (Groups I+II+III vs IV: p<0.02). Chlamydia trachomatis IgA-IPA containing sera also had specific IgG-IPA antibodies (≥1∶80) in 29 (96%) out of 30 sera from HLA-B27 positive individuals and controls. Conversely, 45% of specific IgG-positive (≥1∶80) AS sera, 27.7% sera in Group II, 39.4% Group III sera vs. 11.1% of sera in Group IV had concomitant chlamydial IgA (≥1∶20). The differences in the prevalence of specific IgA were statistically significant: Group I vs. IV: p<0.01; Group III vs. IV: p<0.05 and Gr. I+II+III vs. IV: p<0.05. Our data suggest an enhanced antibody production against Chlamydia trachomatis among the HLA-B27 positive individuals whether they have AS or are healthy.