A MOUSE AMINOPEPTIDASE-N IS A MARKER FOR ANTIGEN-PRESENTING CELLS ANDAPPEARS TO BE COEXPRESSED WITH MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-II MOLECULES

To analyze the expression of mouse aminopeptidase N (APN) on the cells of the immune system a panel of rat monoclonal antibodies against mou se intestinal APN was generated. These antibodies were used to affinit y purify functional mouse APN from both intestine and kidney, and by f low cytometry to examine the APN expression of the cells of the mouse immune system. An APN closely related, perhaps identical, to the intes tinal APN was expressed on a subpopulation of spleen cells and stimula ted peritoneal exudate cells, primarily representing antigen-presentin g cells, such as B cells, macrophages, dendritic cells, and veiled cel ls. In contrast this APN expression could not be detected on thymocyte s or spleen T cells. As a corollary, APN was expressed on monocyte, ma crophage, and B lymphoma cell lines, but not on T hybridoma or thymoma cell lines. The expression of APN showed a striking correlation with the MHC class II expression in all the cell populations studied. This apparent co-expression suggests a role tor APN in antigen processing.