Characterization of the humoral immune response to Chlamydia outer membrane protein 2 in chlamydial infection

Abstract

Detection of antibodies to an outer membrane protein 2 (OMP2) by enzyme-linked immunosorbent assay (ELISA) by using either the Chlamydia trachomatis- or the Chlamydia pneumoniae-specific protein was investigated. OMP2 is an immunodominant antigen giving rise to antibody responses in humans infected with different C. trachomatis serovars (A to C and D to K) or with C. pneumoniae, which could be detected by OMP2 ELISA. OMP2 ELISA is not species specific, but antibody titers were usually higher on the homologous protein. The sensitivity of this assay was high but varied according to the "gold standard" applied. Levels of antibody to C. pneumoniae OMP2 as detected by ELISA seem to return to background or near-background values within a shorter period of time compared to antibodies to C. pneumoniae detected by microimmunofluorescence (MIF), making it more likely that positive results in ELISA reflect recent infection. Thus, OMP2 ELISA has distinct advantages over MIF and commercially available ELISAs and might be a useful tool for the serodiagnosis of chlamydial infection.

FIG. 1.

(A) Distribution of antibody titers to OMP2 in 16 patients with trachoma (C. trachomatis serovars A to C), 12 patients with urethritis, 4 patients with sexually acquired reactive arthritis (C. trachomatis serovars D to K), and 4 patients with acute C. pneumoniae infection as measured by ELISA on the homologous protein. In all patients, acute infection with C. trachomatis or C. pneumoniae was proven by IDEIA, LCR, culture, or PCR, respectively. The cutoff was defined as the mean of negative control sera + 2 SD. (B) Distribution of antibody titers to OMP2 (C. trachomatis and C. pneumoniae OMP2), as measured by ELISA on the protein indicated, in 100 healthy blood donors (median age, ca. 30 years), 93 patients from The Gambia (median age, 20 years), and 100 patients with stable angina (median age, 68 years), who were otherwise healthy and had no recent history of myocardial infarction. The cutoff was defined as the mean of negative control sera + 2 SD.

FIG. 2.

Longitudinal study showing the distribution of antibody titers of serial serum samples from four patients with acute C. pneumoniae and one patient with acute C. trachomatis infection. The cutoff was defined as the mean of negative control sera + 2 SD.

FIG. 3.

Distribution of antibody titers to C. trachomatis OMP2 in sera from patients with suspected C. trachomatis-associated urethritis attending the local genitourinary clinic, whose vaginal or urethral swab tests were positive or negative for chlamydiae by LCR and EIA. The cutoff was defined as the mean of negative control sera + 2 SD.