Identification of immunogenic antigen candidate for Chlamydophila pneumoniae diagnosis.

Chlamydophila pneumoniae is a Gram-negative intracellular obligate human pathogen and accounts for 5-10% of cases of community-acquired pneumonia. However, isolating and culturing this pathogen is difficult, so there have been several studies searching for new biomarkers for its diagnosis. In this study, we obtained immunogenic proteins of C. pneumoniae KNIH-1 for diagnosis using immunoproteomics. C. pneumoniae infection sera were selected for the highest index value of C. pneumoniae-specific IgG using microimmunofluorescence (MIF). The detected protein spots in common from C. pneumoniae infection sera using proteome analysis were identified as Omp11, type III secretion system ATPase, and PmpG by LC-MS/MS and MS databases. They were selected as candidate antigens. In addition, using in silico prediction we also identified proteins encoded by Omp11, PmpG and IncA as antigens. And then, IncA acts as an effector by a type III secretion system ATPase, as identified by mass spectrometry, and was selected as a candidate antigen. Thus, we predict proteins encoded by Omp11, the PmpG family and by IncA as candidate diagnostic immunogens.