ANPEP (also known as CD13, AAP, AP-N, LAP1, and P150) is a broad specificity alanyl aminopeptidase involved in the final digestion of peptides generated from hydrolysis of proteins by gastric and pancreatic proteases. It is thought to function in the metabolism of regulatory peptides of diverse cell types, responsible for the processing of peptide hormones (angiotensin III and IV), neuropeptides, and chemokines. It is thought to play an important role in the pathogenesis of cholesterol gallstone disease. ANPEP also cleaves antigen peptides bound to major histocompatibility complex class II molecules of presenting cells and serves to degrade neurotransmitters at synaptic junctions. Is also implicated as a regulator of IL-8 bioavailability in the endometrium, and therefore may contribute to the regulation of angiogenesis. It is used as a marker for acute myeloid leukemia and plays a role in tumor invasion. It is also a useful and specific marker for mature zymogenic chief cells (ZCs) present in gastric epithelium, and expression on ZCs is lost in transition to metaplasia in the stomach. In immunohistochemistry of normal tissue, ANPEP has membranous and cytoplasmic positivity in the prostate, liver, gallbladder, exocrine pancreas, intestine and renal tubules. References: The UniProt Consortium. Nucleic Acids Res. 47: D506-515 (2019); Nucleic Acids Res. 2016 Jan 4;44(D1):D733-45, PMID:26553804; Am J Physiol Gastrointest Liver Physiol. 2015 Dec 15; 309(12): G955–G964, PMID: 26514774;