CARBOXYPEPTIDASE-M AS A MARKER OF MACROPHAGE MATURATION

During terminal maturation of blood monocytes (MO) into macrophages (M AC), a multitude of phenotypic and functional changes occur: cells inc rease in size and enhance their capacity for phagocytosis and tumor cy totoxicity, but decrease their ability for T-lymphocyte stimulation. T he pattern of secreted cytokines is shifted as is the profile of surfa ce antigens. The identity of the MAC maturation-associated antigen MAX .1/MAX.11 with carboxypeptidase M (CPM), a phosphoinositol-linked endo peptidase, was recently described. CPM is able to process a multitude of different substrates, among them immunologically important peptides such as bradykinin, anaphylatoxins and enkephalins. It was previously shown to be expressed in placenta, lung and kidney. CPM as detected b y MAX.1/11 shows a strong expression on MO-derived MAC in vitro and on MAC in vivo accompanying T-lymphocyte activation such as during allog eneic transplant rejection or allergic alveolitis. In contrast, its ex pression is suppressed on MAC by some types of tumor cells. A synchron ous expression of CPM together with MAC cytotoxic function makes a fun ctional relationship very well possible. However, the biological impor tance of CPM expression on MAC in vivo is difficult to predict, since a nide range of biologically active peptides are substrates for CPM, a nd the relevance for most of those peptides to be processed by CPM dur ing an immune reaction is only poorly understood at present.