HERV-K Env-induced apoptosis was blocked by CD98 monoclonal antibody in SH-SY5Y cells. For the determination of apoptotic cell death, Apopxin Green staining was used as a measure of apoptotic body release. Images were analyzed using Imaris software and show staining of Apopxin Green which labels phosphatidylserine (PS) on the cell surface of apoptotic cells (green), and CytoCalcein Violet labels the cytoplasm of living cells (blue). A, Qualitatively, HERV-K Env (30 nM) increased apoptotic body release (Apopxin Green), and these increases were blocked by pretreatment (30 min) with CD98 monoclonal antibody (CD98 mAb, 0.2 µg). B, Quantitatively, apoptotic cells as indicated by Apopxin green staining were significantly (p < 0.0001) increased by HERV-K Env (30 nM); these increases in Apopxin green staining were blocked by pretreatment (30 min) with CD98 monoclonal antibody (CD98 mAb, 0.2 µg). C, Controls including buffer, preincubation of HERV-K Env with the K01 antibody for 2 h at 4°C (antibody-inactivated HERV-K Env), and heat-inactivated HERV-K Env (15 min at 95°C) did not significantly induce apoptosis. An ANOVA with Tukey's post hoc multiple-comparisons test was used for analysis. Each data point represents the mean fluorescence of 30 cells performed independently five times for each group (n = 150). n = total number of cells for each group plotted. Cells were chosen randomly in the microscope's field of view and no cells were intentionally excluded. Scale bar = 20 µm. B, F_(3,16) = 24.76, p < 0.0001; (C) F_(2,12) = 0.5139, p = 0.6108.