Differences in IgM surface expression pro-files and B-cell receptor (BCR) component glycosylation status between chronic lymphocytic leukemia (CLL) patients and healthy subjects.

(A) Flow cytometry analysis of surface IgM staining. Results from a representative patient weakly expressing IgM, and from a representative healthy subject are shown.

(B) Glycosylation analysis of BCR components. Cell extracts (20 g) produced by lysis in modified bovine serum (MBS) were incubated at 37°C in the presence (+) or absence (−) of Endo-H and separated by 10% SDS-PAGE, and the resulting protein bands were transferred to nitrocellulose. Filters were probed with mAbs as follows: rabbit anti-m heavy chain, mouse anti-CD79a (CD79a), or anti-CD79b (CD79b), and immunoreactive bands were detected with an appropriate horseradish peroxidase–linked secondary antibody. Immature glycosylated (dotted arrows) and mature glycosylated (solid arrows) proteins are indicated for each staining. Forms deglycosylated by Endo-H treatment are indicated by #. Molecular masses are indicated in kilodaltons (kDa). The asterisk indicates a nonspecific band at 30 kDa constantly observed with the anti-CD79b probe from Pharmingen. It is shown that a majority of m and CD79a chains produced by CLL B cells are still sensitive to Endo-H, indicating that they are immature.

This contrasts with normal B cells where a majority of m and CD79a molecules are resistant to Endo-H. Interestingly, no defect in glycosylation could be found for CD79b molecules.