C3 and infection: In both C3−/− and FcγR−/− mice that were previously vaccinated or infected with B. pertussis, the B. bronchiseptica bacterial load in the lungs was significantly decreased by Day 3 post-inoculation when compared to naïve mice (Figure 4), indicating that either vaccination or infection can confer protection in the absence of either C3 or FcγRs.