Inflammatory- and immune responses in relation to bacterial replication in mice following re-infections with Chlamydophila pneumoniae

Objective: Investigation of chronic infections with Chlamydophila pneumoniae. Methods: BALB/c mice were repeatedly infected with C. pneumoniae and tested during a 1-year period. Production of histamine, IFN-γ, IL-6 and antibodies was monitored by ELISA. Live bacteria were cultured and DNA was detected by PCR. Cellular immunity was tested by ELISPOT. Results: After re-infections, culture positivity and persist- ence of DNA in lungs and blood were shorter. Detection of DNA at late time points indicated persistent infection in a few mice. Histamine was produced after primary and re-in- fections, and the level correlated with the number of viable bacteria in lung. IFN-γ, IL-6 levels, IgG2/IgG1 ratio, IgA titres, and level of chlamydial heat-shock protein antibodies were higher after re-infections. IgM antibodies were demon- strated even after re-infections. High number of IFN-γ-pro- ducing splenocytes was observed after the third inoculation. Conclusion: These results promote an understanding of the patho- and immune mechanisms after C. pneumoniae re-in- fections.