Carboxypeptidase M (CPM) is a membrane-bound ectopeptidase that specifically removes C-terminal basic amino acids (arginine or lysine) from peptides and proteins 1. CPM functions as a phosphoinositol-linked enzyme localized to the cell surface and extracellular compartments, where it processes multiple biologically active substrates including immunologically important peptides such as bradykinin, anaphylatoxins, and enkephalins 1. The enzyme plays important roles in regulating peptide hormone and growth factor activity at the cell surface and in membrane-localized degradation of extracellular proteins. CPM expression serves as a marker of macrophage maturation in vitro and in vivo, with strong expression on monocyte-derived macrophages correlating with macrophage cytotoxic functions 1. CPM is detected on macrophages during T-lymphocyte activation in contexts such as allogeneic transplant rejection and allergic alveolitis, though its expression can be suppressed by certain tumor cells 1. Despite CPM's broad substrate specificity and expression in tissues including placenta, lung, and kidney, the precise biological importance of CPM peptide processing during immune reactions remains poorly understood 1. Notably, CPM expression and function show species-specific patterns, with expression undetectable in murine primary macrophages despite conservation across human tissues 1.