Impaired assembly of IgM with CD79a and CD79b in CLL samples. (A) Human normal naïve B-cell samples (n = 6), U-CLL cell samples (n = 6), and M-CLL cell samples (n = 6) were 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 results in (B-C) represent the relative association of CD79a and CD79b to IgM in U-CLL and M-CLL cell samples (lines represent mean ± SEM of 6 samples), with total IgM-associated CD79a or CD79b protein in human normal naïve B-cell 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 < .005. IB, immunoblot; IP, immunoprecipitated; NB, naïve B cell.