RECEPTORS FOR IGM-COATED ERYTHROCYTES ON CHRONIC LYMPHATIC-LEUKEMIA CELLS

Abstract

Lymphocytes of CLL [chronic lymphocytic leukemia] patients, having typical B [bone marrow-derived] cell characteristics, form rosettes with Ig[immunoglobulin]M-coated bovine erythrocytes (E). Of 18 investigated patients, 3-78% (mean 29%) of the isolated lymphocyte reacted with EA[E, antibody]-IgM. With mixed rossette assays, EA-IgM was bound to cells bearing receptors for IgG as well, but not to SRBC [sheep red blood cell] receptor-bearing lymphocytes. Rosette formation could be completely blocked by addition of IgM at concentrations as low as 0.17 mg/ml. Aggregated human IgG [10 mg/ml] had no effect on the rosette formation with EA-IgM, but completely abolished the binding of EA-IgG. Adult human or rabbit serum blocked the EA-IgM binding, whereas cord blood serum and FCS [fetal calf serum] had no effect. EA-IgM binding probably does not occur via a somewhat altered IgG-Fc receptor but reacts with different membrane structures. EA-IgM receptor can be cleaved off with trypsin and can be reconstituted after overnight cultivation. In contrast to the situation in normal subjects, in CLL patients the IgM receptors are demonstrable before overnight cultivation and are found on cells with B cell characteristics.