Surface CD107a renders cells less sensitive to NK cell–mediated lysis. (A) Surface CD107a reduces NK cell lysis of target cells. Top: Surface expression of CD107a on the indicated transfected cells was tested by FACS analysis using anti-CD107a antibody (black) or isotype control (shaded). Bottom: 4-hour 51Cr release assay using IL-2–activated human NK cells with HeLa (left) or 721.221 (right) target cells, stably expressing surface CD107a (triangles) or Clec12B as a control (squares), at the indicated effector to target (E/T) ratios. Values represent triplicates ± SD; statistical analysis was performed using 2-way analysis of variance (ANOVA); n = 5. From low to high E/T, the P values are: nonsignificant .0009; < .0001; and < .0001 (for HeLa cells); and nonsignificant .0315; .0002; and < .0001 (for 721.221 cells). (B) Degranulation induced by sCD107a-expressing target cells. IL-2–activated human NK cells were incubated for 3 hours with HeLa (left) or 721.221 (right) cells expressing either Clec12B (CTRL) or sCD107a in the presence of anti-CD107a antibody. CD107a externalization on CD56+ events was assessed; means ± SEM statistical analysis was performed using the unpaired 2-tailed Student t test; n = 6. (C) 721.221 cells expressing low levels and high levels of sCD107a were incubated for 4 hours without (left) or with (right) IL-2–activated human NK cells. Cells were stained for CD56 and CD107a, followed by Annexin-V staining. Shown are the events of the CD56– gate; n = 3 independent experiments.
