Biochemical and Functional Characterization of MCS-2 Antigen (CD13) on Myeloid Leukemic Cells and Polymorphonuclear Leukocytes1

The antigen defined by MCS-2 monoclonal antibody (niAh) was char acterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of surface and internally labeled cells. Surface iodination revealed that MCS-2 antigen on the surfaces of acute myelogenous leukemia cells, III 61) cells, and polymorphonuclear leukocytes (PMN) had the same molecular weight (.Vf, 150,000) and that their autoradiographic bands were also the same. Internal labeling of 111.-60 cells with |-"S|mcthiuninc followed by immunoprecipitation revealed two bands whose molecular weights were 150,000 and 130,000.1II .-60 cells gave stronger bands than did PMN. The intensity of the M, 130,000 band became weaker, when internally pulse-labeled cells were cultured in the absence of labeled methionine, suggesting that M, 130,000 glycoprotein was a precursor protein of M, 150,000 glycoprotein. MCS-2 niAh precipitated two bands from tunicamycin-treated 111-60 cells whose apparent molecular weights were 100,000 and 110,000. When cells were cultured with MCS-2 niAb, expression of the antigen decreased rapidly (within 10 min). The degree of suppression was more prominent in PMN than in acute myelogenous leukemia and in myelomonocytic cell lines. Reexpression of MCS-2 antigen by PMN after removal of the m Vb from the culture medium was not observed, but it occurred rapidly in myelomonocytic cell lines, although it was blocked by pretreatment of the cells with cycloheximide. These findings suggested that the less-marked suppression of MCS-2 antigen expression by cell lines was due to its greater synthesis by these cells. These findings suggested that MCS-2 mAh reacted with identical molecules, which were recognized by other niAbs belonging to (1)13. Furthermore, modulation of MCS-2 antigen was observed by MCS-2 mAb itself.