Molecular biology of Chlamydia pneumoniae surface proteins and their role in immunopathogenicity

Background The association of Chlamydia pneumoniae with the development of atherosclerosis is based on serology and on detection of C pneumoniae-speci fic DNA by polymerase chain reaction in the atheromas. Methods and Results Because the humoral immune response frequently recogniz es epitopes present on the surface of the bacteria, we analyzed what compon ents are present on the C pneumoniae surface. We identified a family of pro teins, the GGAI or Omp4-15 proteins, of which at least 3 are present on the surface of C pneumoniae. We immunized rabbits with recombinant GGAI protei ns and used these antibodies in immunofluorescence microscopy of experiment ally infected mice. In lung sections, a massive infiltration with polymorph nuclear neutrophil cells was observed. In the bronchial epithelial cells, C pneumoniae inclusions were seen. Evidence was found of differential expre ssion of the GGAI proteins. Conclusions On the basis of surface localization, differential expression, and the fact that the proteins are recognized by the human humoral immune r esponse, we speculate whether these proteins, in addition to the lipopolysa ccharides, are of importance for the immunopathogenesis of C pneumoniae.