CD38 is laterally associated with CD19, but not with CD5, CD20, and CD31. B cells purified from 6 different CD38⁺ CLL patients were cultured for 3 days in the presence of 100 IU/mL IL-2 to increase CD38 expression. CD38 capping was induced on ligation with the IB4 mAb followed by binding with a TRITC-conjugated GαMIg for 30 minutes at 37°C (red). After blocking the experiment with the addition of cold PBS plus 0.1% NaN₃, directly FITC-conjugated mAbs to CD19, CD5, CD20, and CD31 were added for 20 minutes at 4°C (green). The cells were then fixed and analyzed with an Olympus 1 × 70 microscope using the ANALYSIS software. The panels on the right show the merge of the 2 images. Original magnification × 60.