Analysis of the humoral immune response to Chlamydia outer membrane protein 2

Abstract

The humoral immune response to Chlamydia outer membrane protein 2 (Omp2) was studied. Omp2 is a highly genus-conserved structural protein of all Chlamydia species, containing a variable N-terminal fragment. To analyze where the immunogenic parts were localized, seven highly purified truncated fusion proteins constituting different regions of the protein were produced (Chlamydia pneumoniae-Omp2aa23-aa93, Chlamydia psittaci-Omp2aa23-aa94, and Chlamydia trachomatis-Omp2aa23-aa84, aa87-aa547, aa23-aa182, aa167-aa434, aa420-aa547). By an enzyme-linked immunosorbent assay with serologically defined patient sera, Omp2 was found to be a major immunogen of both C. pneumoniae and C. trachomatis infections (P < 0.0001). The humoral immune responses were not confined to any particular region of the Omp2 protein, and no species-specific anti-Omp2 immunoglobulins were detected.

FIG. 1

Homology in the Omp2 protein of Chlamydia pneumoniae (IOL-207), C. psittaci (6BC), and C. trachomatis (L2). Homology among all species is indicated in black in the top band, whereas heterology is indicated in white. Genus homology (%) and the situation of each fusion protein produced are illustrated below. pn, pneumoniae; ps, psittaci; tr, trachomatis.

FIG. 2

SDS-polyacrylamide gel electrophoresis of purified Omp2 fusion proteins. Lanes: 1, C. pneumoniae-Omp2_aa23-aa93; 2, C. psittaci-Omp2_aa23-aa94; 3, C. trachomatis-Omp2_aa23-aa84; 4, C. trachomatis-Omp2_aa87-aa547; 5, C. trachomatis-Omp2_aa23-aa182; 6, C. trachomatis-Omp2_aa167-aa434; 7, C. trachomatis-Omp2_aa420-aa547. Molecular size markers are indicated to the left (lane 0).

FIG. 3

Serological data representing all four serum groups. Titers obtained using C. trachomatis antigen in microimmunofluorescence are illustrated by bars in panel A and titers of C. pneumoniae-MIF are indicated by bars in panel B. ELISA readings, using C. trachomatis-Omp2_aa87-aa547 as the coating antigen, are represented in panel C. Sera were diluted 1/1,000 for the ELISA measurements. Solid lines indicate 125% of the mean OD₄₅₀ value obtained by group IV (MIF-negative sera).

FIG. 4

Antibodies towards C. trachomatis-Omp2_aa23-aa182 (black bars), C.trachomatis-Omp2_aa167-aa434 (grey bars), and C.trachomatis-Omp2_aa420-aa547 (white bars) as measured by ELISA with selected patient samples. Serum dilution, 1/1,000.