CD226-deficient NK cells show impaired cytotoxicity at the single cell level. (A) Unstained NK cells (unsorted WT, CD226+ WT, CD226− WT, or Cd226−/− NK cells) and calcein AM–stained B16F10 cells (transfected with CD155 siRNA or not) were imaged every 2 min from 1 h to 5 h. Representative photos are shown (magnification, 200 ×; scale bars, 50 μm, n = 10 movies of 3 independent experiments per group). (B) Representative images show dying of cancer cells (original magnification, 200 ×; electronically zoomed). Cancer cells underwent rounding and propidium (PtdIns) uptake phases. Ratios of rounding and PtdIns uptake cells were counted every 1 h. (C) Time needed for cells to become rounded morphology was calculated (n = 129, 59, 4, 13, and 22 from the left). (D) Time needed for rounded cells to uptake PtdIns was calculated (n = 101, 81, 4, 6, and 21 from the left).