Age- and sex-matched wild-type C57BL/6 mice were infected subcutaneously with 104 CFUs of F. novicida wild-type or strains deficient for the putative effectors, and the bacterial burden in the liver and spleen as well as serum IL-18 levels were assessed at 2 days post infection (Fig. 6d,e). This evidence concerns the gene IL18 and infection.