BCR and B-cell chronic lymphocytic leukemia: In addition, abundance of the IG constant region mu and delta (IGHM and IGHD) and CD79B, part of the B cell receptor (BCR) complex, was higher in U-CLL, in concordance with the higher surface IgM expression and BCR responsiveness observed in these patients.23,24 In contrast to previous research,25 MARCKS was not differentially abundant between U-CLL and M-CLL patients in our cohort (Suppl.