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

Abstract

The role of gamma interferon (IFN-gamma) 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-gamma 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-gamma neutralization in both mouse strains. Thus, the effect of IFN-gamma neutralization was dependent on the genetic background in primary infection. However, IFN-gamma appeared to be equally important in both mouse strains during reinfection.

FIG. 1

Medians (bars) and upper and lower quartiles (error bars) of C. pneumoniae culture results after primary challenge (A) or rechallenge (B) (given 33 and 63 days after primary challenge to BALB/c and C57BL/6 mice, respectively) with 10⁶ IFU of C. pneumoniae are shown for IFN-γ-neutralized (white bars) and untreated (gray bars) BALB/c and C57BL/6 mice. Data are from single experiments with 10 and 6 to 8 mice per group at each time point in BALB/c and C57BL/6 strains, respectively. In addition, accumulated data describing mean culture results from several different experiments (resulting in 15 to 43 and 10 to 18 mice per time point in BALB/c and C57BL/6 strains, respectively) are presented as a reference for general infection kinetics in immunocompetent mice (line) (the data for BALB/c mice have been described previously [17]). ∗, statistically significant difference between IFN-γ-neutralized mice and untreated control mice, as evaluated by Mann-Whitney U test (P = 0.01 and 0.003 [A] and P = 0.002, 0.04, and 0.028 [B]); BD, below detection limit; ND, not determined.