IL4 and infection: Following infection, significant increases in basophils and eosinophils were noted by day 4 p.i. (Fig. 4A and B), the same day that elevated MCs were first observed in the ileum (Fig. 3A), with both basophils and eosinophils declining to control levels by day 8 p.i. Basophils are rare c-kit receptor-negative, FcεRI-positive cells that mature in the bone marrow and that, upon activation, release histamine, lipid mediators, and chemokines, as well as IL-4 and IL-13 (46, 47).