The WM-15 monoclonal antibody specifically reacts with human CD13, 150-170 type II transmembrane ectoenzyme also named aminopeptidase N and gp150. It is expressed by granulocytes and monocytes, epithelial cells, and endothelial cells. CD13 plays a role in the terminal degradation of peptides, antigen processing, and chemokine cleavage, and cellular adhesion.