MITOCHONDRIAL-MEMBRANE PROTEIN DEFINED BY A NOVEL MONOCLONAL-ANTIBODYIS PREFERENTIALLY DETECTED IN APOPTOTIC CELLS

Studies toward the biologic and molecular understanding of programmed cell death have been stimulated by the recent identification of genes and their products that regulate apoptosis. A panel of mAbs has been r aised against dying cells in the present study by immunizing mice with apoptotic Jurkat cells. One of these Abs, anti-7A6, was found to reac t with apoptotic cells. Using ELISA or flow cytometry, little reactivi ty of anti-7A6 was observed in normal or desitonin-permeabilized human peripheral blood lymphocytes and a number of hemopoietic cell lines t ested. The Ab, however, strongly reacted with these cells when they we re induced to undergo apoptosis by irradiation or treatment with apopt osis-inducing agents, Cell sorting and DNA fragmentation experiments r evealed that 7A6-positive cells, but neat 7A6-negative cells, had appa rent DNA fragments characteristic of cells undergoing apoptosis. By im munoblot, under reducing conditions, anti-7A6 detected a 38-KDa protei n band in the cell lysates prepared from apoptotic cells; Immunoelectr on microscopy showed the 7A6 Ag to be localized to the membrane of mit ochondria in apoptotic jurkat cells. These results indicate that anti- 7A6 defines a novel epitope on the mitochondrial membrane protein that appears to he exposed on cells undergoing apoptosis, suggesting that the 7A6 molecule may be involved in the molecular cascade of apoptotic cell death.