Mice infected intratracheally with strain P15 had a significantly higher production of IFN-γ in the lungs at day 7 post-infection (p = 0.025), but significantly lower production of TNF-α in the brain at day 7 post-infection (p = 0.038) compared to mice infected with H99W (Figure 6(a)), suggesting a complex host response. This evidence concerns the gene TNF and infection.