VIP, or vasoactive intestinal peptide, is a neuropeptide of 28 amino acid residues that belongs to a glucagon/secretin superfamily, and it exerts its actions through three G-protein-coupled receptors (PAC1, VPAC1, and VPAC2). VIP is synthesized by trophoblast cells; it regulates trophoblast cell function and interaction with the major immune cell populations present in the pregnant uterus.