Identification of immunoreactive proteins of Chlamydia trachomatis by Western blot analysis of a two-dimensional electrophoresis map with patient sera

Western blots of two‐dimensional electrophoretic maps of proteins from Chlamydia trachomatis were probed with sera from 17 seropositive patients with genital inflammatory disease. Immunoblot patterns (comprising 28 to 2 spots, average 14.8) were different for each patient; however, antibodies against a spot‐cluster due to the chlamydia‐specific antigen outer membrane protein‐2 (OMP2) were observed in all sera. The next most frequent group of antibodies (15/17; 88%) recognized the hsp60 GroEL‐like protein, described as immunopathogenic in chlamydial infections. Reactivity to the major surface‐exposed and variable antigen major outer membrane protein (MOMP) was observed at a relatively lower frequency (13/17; 76%). The hsp70 DnaK‐like protein was also frequently recognized (11/17; 64.7%) in this patient group. Besides the above confirmatory findings, the study detected several new immunoreactive proteins, with frequencies ranging from 11/17 to 1/17. Some were characterized also by N‐terminal amino acid sequencing and homology searches. Amongst these were a novel outer membrane protein (OmpB) and, interestingly, five conserved bacterial proteins: four (23%) sera reacted with the RNA polymerase alpha‐subunit, five (29%) recognized the ribosomal protein S1, eight (47%) the protein elongation factor EF‐Tu, seven (41%) a putative stress‐induced protease of the HtrA family, and seven sera (41%) the ribosomal protein L7/L12. Homologs of the last two proteins were shown to confer protective immunity in other bacterial infections. The data show that immunological sensitization processes commonly thought to play a role in chlamydial pathogenicity may be sustained not only by the hsp60 GroEl‐like protein, but also by other conserved bacterial antigens, some of which may be also considered as potential vaccine candidates.