DPPIV/CD26 is a serine exopeptidase that is expressed as a noncovalent homodimer on the surface of epithelial cells, endothelial cells, and activated lymphocytes. It regulates multiple aspects of immune and endocrine function by cleaving Xaa-Pro or Xaa-Ala dipeptides from the N-terminus of a wide variety of chemokines (CCL4 and 5, CXCL6, 9, 10, 11, and 12), growth factors (GM-CSF, IL-3), and peptide hormones (Glucagon, Glucagon-like Peptides 1 and 2, GIP, GHRH, Procalcitonin, Neuropeptide Y, and Substance P). DPPIV interacts in cis with Adenosine Deaminase on T cells, in trans with Caveolin-1 on antigen presenting cells, and it serves as a cell entry coreceptor for HIV and coronavirus. It provides costimulatory proliferation and activation signals to both CD4+ and CD8+ T cells. A soluble form of DPPIV can be proteolytically shed from adipocytes, leading to insulin resistance in adipocytes and skeletal muscle.