IL-2–mediated NK-cell proliferation as well as SCF + IL-2 proliferative synergy are MAPK dependent. For panels A and B, the y-axis represents the mean percentage proliferation (± SEM) above that measured for untreated controls as measured by the MTS assay. (A) Primary, human NK cells pretreated with either UO126 (10 μM) or DMSO (vehicle) were cultured in SCF, IL-2, or SCF + IL-2. Combined data from 3 independent experiments show mean proliferation (± SEM) in response to IL-2 and in response to SCF + IL-2 was decreased in the presence of the MAPK inhibitor compared with vehicle control (indicated by * in panel A, P < .05 for each comparison shown). (B) Overexpression of ERK1 and ERK2 in the NK-cell line DERL-7 yields complementary results. Overexpression of ERK1 () and ERK2 () led to statistically significant increases in proliferation (± SEM) in response to IL-2 and SCF + IL-2 (comparisons indicated by * respectively in panel B, P < .05 for all indicated comparisons) compared with cells treated with vector alone (□).