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

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.