DPP4 is a cell surface glycoprotein receptor that functions in immune regulation, apoptosis, signal transduction, glucose metabolism and regulation of insulin secretion. It can inactivate GLP-1, PACAP and GIP, which each stimulate insulin secretion in the pancreas and reduce glucose levels. It acts as a positive regulator of T-cell coactivation and induces T-cell proliferation and NF-kappa-B activation, and it is involved in lymphocyte-epithelial cell adhesion. In disease, DPP4 contributes to fibrosis in the liver, kidney and other organs, and it is also deregulated in a number of cancers. Furthermore, it is a target of therapies in diabetes. In immunohistochemistry, DPP4 has luminal membranous positivity in the parathyroid, small intestine, kidney, endometrium, placenta and prostate. References: Journal of Gastroenterology. 2014. 49 (3): 481–91, PMID: 23475323; Front Immunol. 2015; 6: 386, PMID: 26284071