In response to WT infection, there was a 20-fold increase above controls in IFN-γ gene expression on day 4 and a 60-fold increase by day 7, significantly higher than that in response to ΔPT infection (5-10-fold increase above control) (Fig. 4E), indicating that PT induces Th1 as well as Th17 responses during B. pertussis infection. Here, IFNG is linked to infection.