Analysis of the humoral immune response to Chlamydia pneumoniae by immunoblotting and immunoprecipitation

Chlamydia pneumoniae is a widely spread agent of respiratory tract infectio ns in humans. A reliable serodiagnosis of the disease is hampered by the po or knowledge about immunodominant antigens in C. pneumoniae infections. We applied a novel strategy to identify immunogenic proteins of C. pneumoniae TW183 combining metabolic radiolabeling of de novo-synthesized chlamydial a ntigens with immunoprecipitation. By this technique C. pneumoniae antigens of approximately 160, 97 to 99, 60 to 62, 40, 27, and 15 kDa were detected in the vast majority of sera from patients with a current C. pneumoniae inf ection. By immunoblotting purified elementary bodies of C. pneumoniae TW183 with the same sera, only the 60- to 62-kDa antigen could be detected consi stently. Sequential immunoprecipitation performed at different stages of th e chlamydial developmental cycle revealed that the 60- to 62-kDa antigen is strongly upregulated after 24 to 48 h of host cell infection and is presen ted as a major immunogen in both C. pneumoniae-infected patients and mice. We conclude that, due to its high sensitivity and concurrent preservation o f conformational epitopes, metabolic radiolabeling of chlamydial antigens c ombined with immunoprecipitation may be a useful method to reveal important immunogens in respiratory C. pneumoniae infection which might have been mi ssed by immunoblot analysis.