B2M and colitis: The absolute requirement of CD4+ T cell responses during C. rodentium infection has been reinforced by the observations that CD4+ T cell-deficient mice (CD4-/-), but not CD8+ T cell-deficient mice (β2m-/-), showed greater susceptibility to C. rodentium-induced colitis and increased systemic dissemination of the bacterium to extra-intestinal sites [16].