CXCL12 induces pronounced MEK activation in ZAP-70⁺. CLL cells were exposed to 30nM CXCL12 for 0-60 minutes at which point the cells were harvested, and the lysates were analyzed for p-MEK protein expression by enzyme-linked immunoabsorbent assay. Depicted is the absorbance measured at 450 nm. Results are shown as mean ± SD of ZAP-70⁻ CLL samples (n = 7) and ZAP-70⁺ CLL (n = 8); * indicates a statistically significant difference; P < .05 paired Student t test. Two-way analysis of variance was used for the comparison ZAP-70⁺ CLL vs ZAP-70⁻ CLL at 3 minutes. (Right) The integral under the time curve was measured as described in “Methods” and is depicted for all ZAP-70⁺ and ZAP-70⁻ CLL cases shown on the left. Data shown are median ± SD; * indicates a statistically significant difference; P < .05 unpaired Student t test.