Studies using VPAC2 receptor knockout mice and transgenic mice overexpressing the VPAC2 receptor have revealed that the receptor regulates the balance between T-helper type 1 and 2 lymphocytes (Th1 and Th2 cells) by stimulating production of more Th2-type cytokines, which mediate hypersensitivity reactions (e.g. allergy) [57,58]. This evidence concerns the gene VIPR2 and allergic disease.