Thus, if the level of serum antibodies was normalized to the number of B lymphocytes present in the spleen, i.e. cells with the potential to secrete pathogen specific antibody, the perinatal lethal mice had considerably elevated levels of circulating IgM and IgG compared to wild type, Tg, and KO mice, consistent with an ongoing infection (Fig. 7C, D). Here, CD40LG is linked to infection.