Phospholipid hydroperoxides are required precursors for TNFα-stimulated Az-PC accumulation. A, DPI abolishes TNFα-induced Az-PC accumulation. Jurkat cells were treated as stated with DPI and TNFα or not for 24 h before Az-PC was determined by mass spectrometry as in Fig. 6. n = 3; *, p < 0.05. B, NOx4 knockdown suppressed TNFα-initiated phospholipid fragmentation. Az-PC was quantified by mass spectrometry in cells with reduced NOx4 or cells expressing scrambled siRNA. n = 6; *, p < 0.05. C, siRNA knockdown of GPx4 enhances TNFα-initiated phospholipid truncation. GPx4 RNA and protein were reduced by siRNA before Az-PC was quantified. n = 6; *, p < 0.05. D, GPx4 overexpression abolishes TNFα-induced accumulation of Az-PC. Az-PC content after transient GPx4 or empty vector transfection with or without TNFα stimulation. n = 6; *, p < 0.05. Error bars, S.E.