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Studies on Monoclonal Antibodies

II. Immune Complex (IgM-IgG) Cryoglobulinemia: The Mechanism of Cryoprecipitation¹

From the Evelyn L. Overton Hematology-Oncology Laboratory, Department of Internal Medicine, The University of Texas Southwestern Medical School, Dallas, Texas 75235

Abstract

Factors influencing the precipitation of a mixed cryoglobulin formed by the interaction of a Waldenström macroglobulin antibody (IgM_Sie) with its antigen (human IgG) have been studied. Binding of Fabµ_Sie fragments to a G1, myeloma protein in the analytical ultracentrifuge showed that the IgG antigen was effectively univalent. Consequently, IgM(IgG)₁₀ is the largest potential complex that can form in this system. Experiments performed by the method of equilibrium molecular sieving demonstrated that primary affinity of antibody combining site for antigenic determinant exhibits modest temperature dependence similar to that observed in other antigen-antibody systems. Solvent ionic strength and change in pH near neutrality did not significantly alter the association constant. By contrast, precipitation of the IgM_Sie-IgG complex was profoundly affected by variation in temperature, ionic strength, and pH. Larger complexes were required for precipitation to occur when the reaction was carried out under non-optimal environmental conditions or when certain IgG antigens were employed. These results indicate that the cryoprecipitating phenomenon is explicable by the finite size and limited solubility of the IgM-IgG immune complexes.

Footnotes

¹ Aided by Grant ET-62 from the American Cancer Society and by the Texas Heart Association.

² This work was done during the tenure of an Established Investigatorship of the American Heart Association.