Transfection of ZAP-70⁻ CLL cells with plasmid DNA encoding ZAP-70 or various mutant forms of ZAP-70. Left column shows schematics of ZAP-70 and each of the various ZAP-70 mutants used in these studies. Middle column shows the histogram depicting the autofluorescence of the control vector–transfected CLL cells (shaded histogram) and fluorescence of the cells stained for ZAP-70 (open histogram). Right column shows changes in calcium flux ([Ca²⁺]_i) of each CLL sample that is observed upon treatment with anti-μ, as in Figure 4A. (A) CLL cells transfected with the empty control vector pcDNA3. (B) CLL cells transfected with pZAP-70. (C) CLL cells transfected with pZAP-70-KA³⁶⁹. (D) CLL cells transfected with pZAP-70-SH2. (E) CLL cells transfected with pZAP-70-SH*.