IL-2 up-regulates CD38 expression in purified B-CLL cells. Cytofluorographic analysis of CD38 expression (gray histograms) in purified B cells from 24 CLL patients. B cells were purified from peripheral blood mononuclear cells by negative selection and stained with an anti-CD38 mAb followed by an FITC-conjugated GαMIg. The same cells were cultured for 3 days in the presence of 100 IU/mL IL-2 and re-evaluated for CD38 expression (open histograms). Analysis was carried out using a FACSort and scoring at least 5000 events/sample. The no. label refers to Table 1.