NEUTROPHIL APOPTOSIS INDUCED BY PROTEOLYTIC-ENZYMES

In this study, we show that three proteolytic enzymes of different spe cificity-pronase, chymotrypsin, and trypsin-induced a dramatic stimula tion of neutrophil apoptosis as shown by morphologic characteristics, analysis of cell DNA content, and presence of a characteristic ''ladde r'' pattern of DNA fragmentation. The action of either chymotrypsin or trypsin was completely prevented by the serine protease inhibitor apr otinin, indicating that the proteolytic activity of the enzymes accoun ts for apoptosis induction. Stimulation of neutrophil apoptosis by pro teases was observed in culture medium supplemented with either inactiv ated fetal calf serum (0.1-50%), autologous serum (0.1-50%), bovine se rum albumin (0.1%), or in protein-free medium. Other cell types such a s human peripheral blood monocytes and lymphocytes, human leukemic cel ls from THP-1, HL-60 and K562 lines, murine L929 fibroblasts, and unst imulated murine macrophages harvested from the peritoneal cavity were not induced to undergo apoptosis after the treatment with proteases. I n an attempt to determine whether neutrophil serine proteases could in duce apoptosis as chymotrypsin and trypsin do, the effect of elastase was assessed. A significant increase in the percentage of apoptotic ce lls was observed in elastase-treated neutrophils. We propose that the selective stimulation of neutrophil apoptosis by proteolytic enzymes m ay play an important role in the normal resolution of inflammation by limiting the autotoxic potential of the neutrophil.