Antibody to Chlamydia trachomatis proteins, TroA and HtrA, as a biomarker for Chlamydia trachomatis infection

We studied whether antibody to two chlamydial proteins (TroA and HtrA) could be used as biomarkers of Chlamydia trachomatis infection. Methods: Recombinant proteins C. trachomatis TroA and HtrA were used as antigens in enzyme immunoassay (EIA). Both IgG and IgA antibody responses were studied. Results: IgG or IgA antibody to either protein was infrequently detected in sera from healthy blood donors or virgin girls. Patients attending the STI Clinic and patients with perihepatitis had often IgG antibody against TroA (25 and 50 % respectively) and HtrA (21 and 38 % respectively). Especially in sera from patients with chlamydial perihepatitis, the A_450nm values with TroA were high (mean 1.591). A positive correlation between C. trachomatis MIF antibody and TroA (r  = 0.7) as well as HtrA (r  = 0.5) antibody was observed in sera from STI clinic patients and perihepatitis patients. Individuals with C. trachomatis infection and positive serology already when seeking medical attention had higher A_450nm values for TroA (0.638) and HtrA (0.836) than patients with no marker of previous exposure or with no infection (0.208 and 0.234 respectively). Diagnosis of genital C. trachomatis infection is often NAAT-based, whereas serology has little value in testing for uncomplicated genital C. trachomatis infection. TroA and HtrA antibodies are potential biomarkers for evaluation of ascending and repeated C. trachomatis infection.