CD4 and infection: The absolute numbers of activated CD4+ and CD8+ T cells in the lungs of infected wild type and IL-4−/− neonates were similar across most time points, though the peak of infiltration of CD4+ T cells around 4 weeks post-infection was consistently up to 2 fold greater in the lung digests of the IL-4−/− pups while the peak in activated CD8+ T cells was higher and earlier in wild type pups (Figure 4C,D).