Vitamin E prevents AICD and suppresses CD95L expression of human peripheral blood T cells. (a) Vitamin E prevents AICD. The day 6 prestimulated peripheral blood T cells were either left alone or pretreated with vitamin E (VE) and subsequently restimulated with α-CD3 (OKT3) in the absence or presence of CD95Fc or control human IgG1. Cell death was assessed after a further 48 hours by propidium iodide uptake. Results represent one experiment done in duplicates. (b) Vitamin E downregulates AICD in a dose-dependent manner. The day 6 T cells prepared from five different donors were restimulated with α-CD3 in the absence or presence of different amounts of vitamin E. Percentage of apoptotic CD4 and CD8 T cells were determined after 36 hours by FSC/SSC analysis. (c) Vitamin E downregulates CD95L protein expression levels. T cells from the donors in b were activated with α-CD3 in the absence and presence of 25 μM vitamin E and metalloproteinase inhibitors to increase expression of the membrane-bound ligand. After 16 hours’ activation, cell-surface expression levels of CD95L protein were measured by FACS. (d) Kinetic analysis of the effect of vitamin E on CD95L protein expression. T cells from donor 3 were activated with α-CD3 in the absence and presence of 25 or 50 μM vitamin E and metalloproteinase inhibitors. Cells were collected at different time points as indicated, and cell-surface expression levels of CD95L protein were measured by FACS.