Do IgA antibodies to Chlamydia trachomatis have protective role in humoral immunity: a study in reactive arthritis patients

Chlamydia trachomatis-induced genitourinary Reactive Arthritis (ReA) can serve as good model for host-pathogen interaction. However, due to poor antigen presentation, cell-mediated immunity does not contribute as anticipated. Present study aims to evaluate protective role of anti-C. trachomatis antibodies vis-a-vis inflammatory chlamydial Major Outer Membrane Protein (MOMP). Prospective study was undertaken in 30 patients with genitourinary ReA. 30 Rheumatoid Arthritis (RA) and 30 osteoarthritis patients constituted controls. Subjects found to be PCR-positive for C. trachomatis were investigated for presence of MOMP in Synovial Fluid (SF) by fluorescence assay while anti-C. trachomatis IgA/IgM antibodies were estimated in SF/venous blood by ELISA. C. trachomatis MOMP was evident by the presence of elementary bodies in SF of 9 ReA PCR-positive patients (30%; p < 0.05 versus controls). Local secretory IgA antibodies were detected in 12 (40%) patients with ReA (p < 0.0001 versus controls); among 12 patients with anti-chlamydial IgA antibodies, 9 showed the presence of both MOMP and IgA antibodies in SF. 58.3% ReA patients (7/12) with secretory IgA antibodies were also positive for circulatory IgA antibodies (p < 0.01 versus controls). Serum IgM antibodies were present in 4 ReA (13.3%) and in 1 RA (3.3%) patient, respectively. In conclusion, the present study suggests that in ReA patients with chronic, persistent C. trachomatis infection in synovium, the chlamydial MOMP is triggering factor for generating a protective immune response by inducing anti-C. trachomatis IgA antibodies in the SF of large number of patients.