p110δ is expressed abundantly in CLL cells. (A) CD19⁺ cells from patients with CLL (n = 20) were examined for p110δ expression by immunoblot. (B) CD19⁺ normal B cells, CD3⁺ normal T cells, CD56⁺ normal NK cells, and CD19⁺ cells from patients with CLL (n = 6 each) were examined for p110δ expression by immunoblot. (C) CD19⁺ cells from patients with CLL (n = 12) and from normal donors (n = 7) were examined for PI3K activity. Horizontal lines represent the mean. Results were calculated relative to microgram of protein.