Soluble forms of CD21 and CD23 antigens in the serum in B cell chronic lymphocytic leukaemia

By using pairs of monoclonal antibodies (MAbs) to different epitopes on CD21 and CD23 antigens, it has been shown that both antigens are readily detectable in cell-free supernates of cultures of B cells expressing these antigens on the cell surface. The antigens remained in the soluble fraction after high speed centrifugation. Sera from normal individuals contained significant amounts of CD21 antigen, whereas little CD23 antigen was detectable. By contrast CD23 but not CD21 antigen was present in urine. Sera from patients with B cell chronic lymphocytic leukaemia (B-CLL) contained increased amounts of both antigens. The levels were related to the surface expression of antigen on the leukaemic cells and the number of cells in the blood. The possible functional role of soluble forms of B cell antigens and the diagnostic potential of their detection in body fluids are discussed.