Enhanced levels of both the membrane-bound and soluble forms of IgM Fc receptor (FcμR) in patients with chronic lymphocytic leukemia.

The association of an IgM-Fc receptor (FcμR) with chronic lymphocytic leukemia (CLL) was suggested more than 30 years ago, but its authenticity has never been formally addressed. We examined the expression of the recently identified FcμR by B and T cells in CLL patients using receptor-specific monoclonal antibodies. CLL B cells (CD5(+)/CD19(+)) expressed much higher levels of FcμR on their cell surface than B cells from healthy donors.