Phosphorylated ERK is uniquely increased in response to SCF + IL-2 as opposed to SCF or IL-2 alone. (A) The top panel shows Western blot results from starved DERL-7 cells stimulated with SCF, IL-2, or SCF + IL-2, suggesting an increase in phosphorylated ERK in response to the combination of cytokines compared with either alone. Actin serves as a loading control. On the bottom, band densitometry reveals statistically significant differences in composite mean (± SEM) phospho-ERK levels (relevant pairwise comparisons indicated by * in panel A, P < .05) from 3 independent experiments. (B) Similar findings are observed in primary human NK cells. Once again, the top panel shows Western blot results for phosphorylated ERK in response to SCF, IL-2, or the combination. On the bottom, band densitometry confirms that composite mean (± SEM) differences from 4 independent experiments shown are also statistically significant (relevant pairwise comparisons indicated by * in panel B, P < .05).