Chlamydia trachomatis serology: diagnostic value of outer membrane protein 2 compared with that of other antigens

Different immunoassays using recombinant antigens or synthetic peptides were evaluated for the serodiagnosis of Chlamydia trachomatis infections. Antigens used included cysteine-rich outer membrane protein 2 (OMP2), heat shock protein 60, the polypeptide encoded by open reading frame 3 of the plasmid (pgp3), synthetic peptides derived from species-specific epitopes in variable domain IV of the major OMP (MOMP) (Labsystems, Helsinki, Finland), and a fragment of the total lipopolysaccharide (Medac, Hamburg, Germany). Because cross-reactions between chlamydial species have been reported, Chlamydia pneumoniae-specific antibodies were also determined by immunoassays (Labsystems). Responses obtained with serum samples from patients with well-defined diseases (i.e., urethral or endocervical samples from which C. trachomatis DNA was amplified) were compared to those obtained with samples from healthy blood donors. The best sensitivity (79%) associated with the best specificity (82%) was obtained when immunoglobulin G (IgG) responses to both MOMP and pgp3 were considered. The highest sensitivity (89%) was obtained with anti-OMP2 IgG, but the lowest specificity (57%) was obtained with this antibody, due to probable cross-reactivity with C. pneumoniae OMP2.