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Receptors for IgM-Coated Erythrocytes on Chronic Lymphatic Leukemia Cells¹

From the Institute for Immunology, University of Vienna, A-1090 Vienna, Austria

Abstract

Our experiments show that lymphocytes of CLL patients, having typical B cell characteristics, form rosettes with IgM-coated bovine erythrocytes. Of 18 investigated patients, 3 to 78% (mean 29%) of the isolated lymphocytes reacted with EA-IgM. With mixed rosette assays, EA-IgM bound to cells bearing receptors for IgG as well, but not to SRBC receptor-bearing lymphocytes.

Rosette formation could be completely blocked by addition of IgM at concentrations as low as 0.17 mg/ml. Ten milligrams per milliliter of aggregated human IgG 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 had no effect.

These inhibition data indicate that EA-IgM binding does not occur via a somewhat altered IgG-Fc receptor but reacts with different membrane structures. That EA-IgM receptor can be cleaved off with trypsin and can be reconstituted after overnight cultivation, also supports this viewpoint.

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.

Footnotes

¹ This work was supported in part by the Austrian Research Council.