IL-4 receptor expression by CLL B cells was increased compared with expression by normal B cells. Purified normal and CLL B cells were freshly isolated as described in Materials and Methods and stained with anti–CD19-PE and anti IL-4R–FITC. Constitutive expression of the IL-4 receptor (solid histogram) relative to isotype staining (open histogram) was determined by gating on CD19⁺ lymphocytes. Data from normal and CLL B cells are representative of three and four samples, respectively.