Kinetic study of antibodies (IgG, IgA) to Chlamydia trachomatis: importance of IgA antibody in screening test for C. trachomatis infection by peptide-based enzyme immunosorbent assay.

To assess the importance of only IgA antibody positivity in the peptide-based ELISA (P-ELISA) examination of kinetic behaviors of antibodies (IgA, IgG) to Chlamydia trachomatis, 426 sera from 52 follow-up antigen-positive patients were assayed. In part, a microimmunofluorescence (MIF) test and an immunoblot (IB) assay were also used for confirmation. The results showed that the positivity rates of IgA and IgG antibodies were 82.7 and 96.2%, respectively, at the first testing. One patient had both IgA- and IgG-negative antibodies at the first testing, but this became only IgA-positive and then IgG-positive. The patient was co-infected with Candida albicans and C. trachomatis, and saw a gynecologist for the symptom of itching. Although the major outer membrane protein was negative in IB assay, the results of the MIF test and absorption experiments were positive. MIF titers for IgA and IgG antibodies to C. pneumoniae were <1:8 and 1:32, respectively, at the peak level of P-ELISA. These findings seem to suggest that when only the IgA antibody is detected by P-ELISA, C. trachomatis infection may be present at an early stage, so confirmation via testing for C. trachomatis is needed.