Quantification of Bax/Bcl-2 ratios in peripheral blood lymphocytes, monocytes and granulocytes and their relation to susceptibility to anti-Fas (anti-CD95)-induced apoptosis

Neutrophils have the shortest half-life among circulating leucocytes and rapidly undergo apoptosis in vitro. The homologous Bcl-2 and Bax proteins have opposing effects, with Bcl-2 extending cellular survival and Bax promoting cell death following an apoptotic stimulus. We determined Bcl-2 to Bax expression ratios in peripheral blood lymphocytes, monocytes and granulocytes and related them to the susceptibility of these cells to anti-Fas (anti-CD95)-induced apoptosis. Here, we show that Bax/Bcl-2 ratios are high in granulocytes and relatively low in monocytes and lymphocytes. Furthermore, we show a relation between this ratio in the different leucocyte subsets and their susceptibility to anti-Fas-induced apoptosis, with granulocytes showing the highest susceptibility, followed by monocytes and lymphocytes. It is concluded that the balance between Bcl-2 and Bax forms an apoptotic rheostat, which seems to determine sensitivity to apoptosis.