Chlamydia pneumoniae major outer membrane protein is a surface-exposed antigen that elicits antibodies primarily directed against conformation-dependent determinants

The major outer membrane protein MOMP of Chlamydia trachomatis serovariants is known to be an immunodominant surface antigen. Moreover, it is known th at the C:. trachomatis MOMP elicits antibodies that recognize both linear a nd conformational antigenic determinants. In contrast, it has been reported that the MOMP of Chlamydia pneumoniae is not surface exposed and is immuno recessive. We hypothesized that the discrepancies between C, trachomatis an d C, pneumoniae MOMP exposure on intact chlamydiae and immunogenic properti es might be because the focus of the host's immune response is directed to conformational epitopes of the C, pneumoniae MOMP. We therefore conducted s tudies aimed at defining the surface exposure of MOMP and the conformationa l dominance of MOMP antibodies. We present here a description of C, pneumon iae species-specific monoclonal antibody (MAb), GZD1E8, which recognizes a conformational epitope on the surface of C, pneumoniae. This MAb is potent in the neutralization of C. pneumoniae infectivity in vitro. Another previo usly described C, pneumoniae species-specific monoclonal antibody, RR-402, displayed vent similar characteristics. However, the antigenic determinant recognized by RR-402 has yet to be identified. We show by immunoprecipitati on of C, pneumoniae with GZD1E8 and RR-402 MAbs and by mass spectrometry an al sis of immunoprecipitated proteins that both antibodies GZD1E8 and RR-40 2 recognize the MOMP of C. pneumoniae and that this protein is localized on the surface of the organism. We also show that human sera from C pneumonia e-positive donors consistently recognize the MOMP by immunoprecipitation, i ndicating that the MOMP of C. pneumoniae is an immunogenic protein. These f indings have potential implications for both C. pneumoniae vaccine and diag nostic assay development.