ZAP-70 expression in CD38⁺ and CD38⁻ cells. PBMCs from 20 elderly healthy donors and 95 patients with CLL were incubated with mAbs to CD5, CD38, CD19, ZAP-70, or appropriate isotype control mAbs. CD19⁺CD5⁺ cells exhibiting a ZAP-70 staining in excess of the isotype control mAbs were considered ZAP-70⁺. (A) Significant differences in percentage of CD5⁺CD19⁺ cells expressing ZAP-70 (P < .001; Mann-Whitney test). These data were further analyzed to determine differences in expression of ZAP-70 between the CD38⁻ and CD38⁺ populations in healthy controls. Horizontal line indicates average of values in corresponding group. (B) and in patients with CLL (C). Significant differences exist between ZAP-70 expression within CD38⁻ and CD38⁺ subsets from healthy donors and patients with CLL (P < .001; Kruskal-Wallis test).