Enhanced CD21 expression and shedding in chronic lymphatic leukemia: a possible pathomechanism in disease progression.

CD21 is a 145-kDa membrane glycoprotein mainly expressed on B cells and follicular dendritic cells, and is involved in B-cell activation, survival and proliferation. CD21 can be cleaved to give soluble CD21 (sCD21), which is constantly shed in healthy persons. We show here that plasma sCD21 levels are higher, while B-cell surface CD21 expression levels are lower in B-cell chronic lymphocytic leukemia (B-CLL) patients, but not in multiple myeloma (MM) patients. High sCD21 levels in the blood are positively correlated to the number of cells with high CD21 surface expression and the relative amount of CD21 expressed on the B cells. B-CLL patients with swollen lymph nodes had higher amounts of CD21 high-expressing B cells, as well as CD21 low-expressing B cells, as compared to B-CLL patients without swollen lymph nodes.