For example, C57BL/6 mice infected via the SC route have detectable plasma IFNγ by day 1 p.i. which peaks at day 4 p.i. followed by a rapid reduction in levels by day 6 p.i. In contrast, following an IN infection, plasma IFNγ cannot be detected until day 3 p.i. but is followed by a rapid increase which continues until death. This evidence concerns the gene IFNG and infection.