Freshly isolated blood NK cells require an additional signal to lyse targets efficiently through NKG2D.

(A) Peripheral blood NK cells fail to kill via NKG2D in the absence of IL-15, but upon stimulation with 10 ng/mL IL-15 they are able to lyse targets in a cPLA2-dependent manner. Blood NK cells from healthy controls were isolated by negative selection and are gated on a CD3^-CD94⁺ background. FACS plots are representative of three independent experiments, summarized on the right. (B) Blood NK cells upregulate cPLA2 basally and are primed to activate cPLA2 more robustly upon activation of NKG2D. Peripheral blood NK cells isolated from healthy controls were stimulated overnight with IL-15 and/or an anti-NKG2D mAb for four hours where indicated, then probed for cPLA2 (left) or phospho-cPLA2 (right). Data are representative of three independent experiments.