IMPLICATION OF ECTOCYTOSIS IN IL-2 RECEPTOR EXPRESSION, PROLIFERATION, AND APOPTOSIS OF HUMAN-LEUKOCYTES

Shedding of plasma membrane or ectocytosis is a ubiquitous process in eukaryotic cells. In this study, we examined the role of vesicles exfo liated from human peripheral blood leukocytes (PBL) in proliferation, expression of IL-2 receptor (CD25) and in the process of apoptosis (pr ogrammed cell death) in these cells. Vesicles derived from peripheral blood leukocytes stimulated with conconavalin (Con)-A induced agglutin ation, IL-P receptor expression and proliferation in leukocytes freshl y isolated from peripheral blood in a fashion similar to that induced by Con-A. These vesicles expressed Con-A on their surface. Furthermore , IL-2 receptor expression induced by concanavalin-A and by vesicles d erived from Con-A activated PBL was inhibited by an antiserum to Con-A suggesting that the activation induced by vesicles is mediated by Con -A bound to their membranes. In contradistinction to these vesicles, t hose derived from IL-2 activated PBL, induced apoptosis in PBL freshly isolated from peripheral blood. The apoptotic leukocytes were identif ied by loss of cell viability, their distinct morphologic characterist ics, and by reactivity with the monoclonal antibody, BM1 that reacts w ith apoptotic cells. These studies implicate vesicles shed from leukoc ytes in the proliferation, expression of IL-2 receptor and apoptosis o f leukocytes.