Antigen-mediated effects on surface IgM of CLL cells. Antigen engagement in tissue sites appears to lead to endocytosis of sIgM in both U-CLL and M-CLL. Endocytic events lead to a modulation of the glycans of the μ-chains with loss of the fully glycosylated form and relative retention of a mannosylated immature form. This retention is more evident in U-CLL where it could mediate new microenvironmental interactions.