No detectable role for endogenous IL-12 during in vitro NK cell stimulation by K562 cells. PBMCs from healthy control individuals were incubated with K562 target cells for 4 hours at 37°C, in the presence or absence of anti–hIL-12 mAb (10 μg/mL). IFN-γ production and CD107 mobilization were assessed in a 4-hour K562 stimulation assay.