Dipeptidyl peptidase IV (DP-IV), also known as CD26, is a serine protease involved in regulating immunity, metabolism, and cell signaling. Its structure includes an active serine site that specifically cleaves peptide chains with proline or serine. DP-IV is primarily expressed on the cell membrane, especially in intestinal epithelial cells, liver, and immune cells. It participates in various biological reactions and signaling pathways, including diabetes and immune regulation. The gene expression of DP-IV is specific, closely related to disease states and tissue types. Mutations or expression changes can affect its function, linking it to various diseases.