CD13 is a 150-170 kD type II transmembrane glycoprotein also known as aminopeptidase N, APN, and gp150. This zinc metallopeptidase is expressed as a homodimer on granulocytes, myeloid progenitors, endothelial cells, epithelial cells and subset of granular lymphoid cells. It is not expressed on platelets or erythrocytes. CD13 is thought to be involved in the metabolism of many regulatory peptides and functions in antigen processing and the cleavage of chemokines such as MIP-1. CD13 serves as the cellular receptor for Coronavirus.