IL-4 promotes IgM maturation in CLL cells. (A-B) IL-4 promotes IgM maturation in CLL samples. U-CLL cells (A, top) and M-CLL cells (A, bottom) were cocultured in the presence (IL-4) or absence (MED) of IL-4 (25 ng/mL) for 48 hours. Viable CLL cells were sorted and lysed in NP-40 buffer. Cell lysates were subjected to endo H digestion followed by immunoblot using anti-IgM antibody to identify endo H-resistant (IgMr) and endo H-sensitive (IgMs) species. The summarized results in (B) represent ratios of IgMr to IgMs in U-CLL and M-CLL cell samples, with or without IL-4 (lines represent mean ± SEM of 6 samples). The results in (A) show 1 representative experiment with 1 U-CLL sample and 1 M-CLL sample. **P < .01; ****P < .001.