IL-4 recovers assembly of IgM-BCR complexes. (A) U-CLL and M-CLL samples 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 extracted in digitonin buffer. IgM protein was immunoprecipitated, and IgM-associated CD79a and CD79b proteins were examined by immunoblot. Membranes were stripped and reprobed with anti-IgM antibody as a loading control. The summarized results in (B-C) represent the relative association of CD79a and CD79b to IgM in U-CLL and M-CLL cell samples with or without IL-4 (lines represent mean ± SEM of 6 samples), with total IgM-associated CD79a or CD79b protein in U-CLL samples set at “1” (lines represent mean ± SEM of 6 samples). The values of IgM-associated CD79a and CD79b are normalized to anti–IgM-precipitated IgM in all samples. The results in (A) show 1 representative experiment with 2 samples of each population. **P < .01; ***P < .005; ****P < .001. IB, immunoblot; IP, immunoprecipitated.