Rag1−/− mice had lower lung levels of IL-6 and IFNγ than wild type C57Bl/6 mice 14 d post-infection (Fig. 4a, b), but levels did not differ significantly between wild-type and Rag1−/− mice on day 0 or 21 post-infection (Fig. 4a, b). This evidence concerns the gene IFNG and infection.