We observed a significant 10-fold increase in the anti-B. pertussis IgM antibody response at day 9 and an almost 20-fold increase 12 days postchallenge in rats infected with D420 compared to the mock challenge, while we also saw a significant 6-fold increase in anti-B. pertussis IgM at day 12 postinfection compared to the amount of anti-B. pertussis IgM from Tohama 1 infection (Fig. 10A). This evidence concerns the gene CD40LG and infection.