The molecular mechanism of cryoprecipitation and cold agglutination of an IgM lambda Waldenström macroglobulin with anti-Gd specificity: sedimentation analysis and localization of interacting sites.

The physicochemical properties and immunologic specificity of an IgM lambda cryoglobulin with cold agglutinin activity (designated MAT) were investigated. Discrete binding sites involved in cryoprecipitation were shown to exist on the reductive 7S subunits and tryptic Fab mu and Fc mu 5 fragments derived from MAT. Analytical ultracentrifugation indicated the nonprecipitating MAT subunits self-associated into rapidly sedimenting paucidisperse boundaries of 32S, 25S, and 8.7S at 13 degrees C, which were converted to a monodisperse 5.7S boundary at 35 degrees C. Furthermore, MAT Fab mu and Fc mu 5 fragments exhibited association with each other at 13 degrees C but not at 35 degrees C when studied by analytical ultracentrifugation. The cold agglutinin activity of MAT can be inhibited by sialyllactose or treatment of erythrocytes with neuraminidase but not papain. Therefore, the membrane determinants of human erythrocytes are Gd (glycolipid-dependent or protease-resistant glycoproteins) with terminal sialic acid. Treatment of MAT with neuraminidase abolished its precipitating properties, but had no effect on its ability to agglutinate untreated erythrocytes. The cryoprecipitation and cold agglutination phenomena exhibited by MAT therefore seem to involve identical or cross-reacting carbohydrate antigens with terminal sialic acid residues.