The Binding of IgM to B Lymphocytes: A Comparison of the Binding Characteristics of IgM Aggregates and EA B (IgM) Complexes to Normal and Leukemic B Lymphocytes 1

Abstract

Abstract

We have compared and contrasted the binding of Agg IgM and heavily sensitized EA_B (IgM) complexes to the Fcμ receptor of normal and neoplastic human lymphocytes. Agg IgM binds uniformly to the entire Smlg⁺ B cell population yet normal lymphocytes require culture in order to achieve binding of EA_B complexes to a subset of Smlg⁺ B cells. In blocking studies IgM complexes and IgM aggregates appear to detect the same receptor and with both reagents binding is influenced by the presence of Mg²⁺ but not Ca²⁺ and is inhibited by EDTA.

The percentage of cells binding EA_B was highest in normal B lymphocyte fractions enriched for C'₃ ⁺ cells (CRL⁺). EA_B binding to cells in the CRL- fractions was negligible even though CRL- fractions contained cells which were Smlg⁺C₃ ^-. EA_B bound only to neoplastic chronic lymphocytic leukemia cells (CLL) that expressed a high percentage of C₃ ⁺ cells. Clones lacking a C₃ receptor failed to bind EA_B. Thus, the binding of EA_B complexes to B lymphocytes appears to be associated principally with a subset that expresses a C₃ receptor whereas IgM aggregates bind to the entire Smlg⁺ B cell population.