Given the lack of overt inflammation observed during infection with cpsII parasites, the absence of parasite-driven cytolysis of host cells, and limited antigen load, it remains surprising that relatively low numbers of these parasites are able to generate strong protective CD4+ and CD8+ T cell responses, comparable to those seen during live infection [31]–[33], [38], [42], [78]. This evidence concerns the gene CD4 and infection.