Synovial fluid and serum antibodies against Chlamydia in different forms of arthritis: intra-articular IgA production in Chlamydia sexually acquired reactive arthritis.

Since the presence of Chlamydia has been shown in synovial fluid (SF) from some patients with Chlamydia reactive arthritis, we investigated whether anti-Chlamydia antibodies present in the joint are derived from the circulation or are locally produced. We compared titres of IgG, IgM and IgA antibodies against Chlamydia, and against a control antigen (tetanus toxoid), by an enzyme-linked immunosorbent assay (ELISA), in paired samples of serum and SF from Chlamydia trachomatis sexually acquired reactive arthritis (CT-SARA) patients and from patients with other forms of arthritis. The ratio of serum/SF IgA anti-Chlamydia antibodies was significantly decreased in CT-SARA patients. It is concluded that, in our experimental conditions, we found evidence for intra-articular production of IgA anti-Chlamydia antibodies.