Detection of antibodies to the major outer membrane protein of Chlamydia trachomatis using an in vitro transcription-translation radioimmunoprecipitation assay

A radioimmunoprecipitation assay (RIPA) using in vitro translated protein was developed to measure serum antibodies to the major outer membrane protein (MOMP) of C. trachomatis. Polyclonal animal antisera to C. trachomatis serovars C, E and F reacted to serogroup-specific determinants by RIPA, as compared to species-specific epitopes by Western blot. Antibody responses in monkeys immunized systemically or mucosally with a candidate MOMP vaccine were assessed by RIPA and ELISA with elementary bodies (EB-ELISA). Unlike EB-ELISA, RIPA showed a significant difference in pre-challenge antibody levels between systemically and mucosally immunized animals. Additionally, only RIPA showed a significant inverse correlation between antibody level at time of challenge and microbiologic response measured as median inclusion forming units (IFU) in culture (r = −0.89; P < 0.001). RIPA using in vitro translated proteins is a useful method to measure antibody responses to specific C. trachomatis antigens and may be more informative than EB-ELISA and Western blot for assessing the immunogenicity of MOMP vaccines.