Western blot analysis of caspase-8, Bid, p27Kip-1, and PARP in IL-21-treated or untreated CLL B cells. (A) An increase of caspase-8 intermediate cleavage fragments (p43/p41) was detected in cell lysates of CD40-activated CLL B cells cultured with rhIL-21 (80 ng/mL) from 3 representative patients. (B) The truncated form of Bid (t-Bid) was observed in cell lysates of CD40-activated CLL B cells cultured in the presence of rhIL-21 (80 ng/mL) from 3 representative patients. (C) Bid expression is induced by 24-hour stimulation with CD40L-expressing cells and persisted for 72 hours, and treatment with IL-21 induces the appearance of t-Bid. (D) p27Kip-1 down-regulation was observed after rhIL-21 treatment (80 ng/mL for 72 hours) in lysates from CD40-activated CLL B cells of 3 different patients. (E) The use of a different Ab, recognizing a p27/Kip1 breakdown product, showed a cleavage product of 23 kDa of p27Kip-1 48 hours after IL-21 stimulation. (F) The cleaved form of PARP observed in CD40-activated CLL B cells after 24 hours of culture with IL-21, was further increased after 48 hours of culture in relationship with the increase of apoptotic cells.