Rituximab induces ERK activation in raft microdomains and p27(Kip1) expression. (A) Raft microdomains of cells treated or not for 15 minutes with 10 μg/mL rituximab were isolated and then immunoblotted with antibodies recognizing ERK (p42/44 MAPK) and phospho-ERK (P-ERK). (i) Light (fractions 1-3); (ii) rafts (fractions 4-6); (iii) intermediate (fractions 7-9); and (iv) heavy (fractions 10-12). (B) Daudi and RL cells (5 × 10⁶) were pretreated or not with 30 μM SR33557 for 1 hour, after which cells were incubated with or without 10 μg/mL rituximab for another 15 minutes. Cells were then immunoblotted with antiphospho-ERK antibody as described in “Materials and methods”; (1) untreated controls, (2) SR33557 alone, (3) rituximab alone, (4) SR33557 and rituximab. (C) Expression of p27(Kip1) was determined by Western blot analysis in Daudi and RL cells; (1) untreated controls, (2) SR33557 alone, (3) rituximab alone, (4) SR33557 and rituximab.