FIG. 5.

Host lethality in C3^−/− mice. To examine in greater detail the in vivo role of complement in this model, C3^−/− and control C3^+/+ C57Bl/6J mice were intratracheally inoculated with 10³ CFU of either wild-type or O-antigen-deficient K. pneumoniae and followed for 96 h for survival. In mice infected with the wild-type bacterial strain, no statistically significant differences were seen between C3^+/+ and C3^−/− animals, suggesting that the complement system was not significantly contributing to host defense. However, C3^+/+ mice enjoyed significantly better survival compared to C3^−/− animals when they were infected with the wbbO mutant (P < 0.05).