Supporting the hypothesis that reduced titer of Ft-specific IgM is responsible for the susceptibility of Il-1r1-/- mice, passive transfer of serum obtained from Ft LVS infected C57BL/6J mice seven days p.i. protected naïve C57BL/6J mice from infection with lethal doses of Ft LVS (Fig. 4D). This evidence concerns the gene CD40LG and infection.