PROLIFERATION AND DEATH OF THYMOCYTES THR OUGH THE ACTION OF THE PHOSPHOLIPASE A(2) ACTIVATOR MELLITIN

The effects of mellitin, a component of bee venom activating phospho9l ipase A(2), on proliferation and death of the rat thymocytes were stud ied in a wide concentration range. Cell proliferation was estimated by the accumulation of colchicine metaphases, Necrosis was estimated by cell lysis and Trypan blue staining. Apoptosis was estimated by the ty pe of DNA fragmentation, amount of fragmented DNA, and percentage of c ells with hypodiploid DNA set. Low concentrations of mellitin (below 5 mu g/ml) stimulated proliferation. At higher mellitin concentrations, the thymocytes die by the primary necrosis type. Mellitin did not ind uce apoptosis in the thymocytes within the concentration range used: o n the contrary, at high concentrations, it inhibited apoptosis of the thymocytes in the control and after irradiation. Actinomycin D, inhibi tor of RNA synthesis, exerted no effect on the thymocyte death in the presence of mellitin. It has been concluded that activation of phospho lipase A(2) may induce necrosis, rather than apoptosis, and consequent ly, activation of phospholipase A(2) is not a necessary step in the si gnalling cascade that initiated apoptosis in the thymocytes.