Acquired immunity to Chlamydia pneumoniae is dependent on gamma interferon in two mouse strains that initially differ in this respect after primary challenge.

The role of gamma interferon (IFN-γ) in a Chlamydia pneumoniae mouse model was studied by in vivo neutralization in two inbred mouse strains. During primary C. pneumoniae infection, neutralization of IFN-γ increased both the numbers of bacteria and the pneumonia score in the lungs of C57BL/6 mice but not BALB/c mice. During reinfection, the bacterial counts in the lungs were increased by IFN-γ neutralization in both mouse strains. Thus, the effect of IFN-γ neutralization was dependent on the genetic background in primary infection. However, IFN-γ appeared to be equally important in both mouse strains during reinfection.