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Interaction of K Lymphocytes with Myeloma Proteins of Different IgG Subclasses¹

From the Department of Immunopathology, Scripps Clinic and Research Foundation, La Jolla, California 92037 and the Department of Immunology, Wenner-Gren Institute, University of Stockholm, Stockholm, Sweden

Abstract

Human myeloma proteins of the four IgG subclasses and their Fc, F(ab)₂, and Fab fragments were tested for their ability to inhibit antibody-dependent human K lymphocytemediated cytotoxicity to chicken erythrocytes (CRBC) sensitized with specific rabbit antibodies. In addition, the adsorption of K cells onto glass bead columns coated with myeloma proteins was investigated. Myeloma proteins and their Fc fragments of all four subclasses inhibited K cell activity. However, there were wide variations within a given subclass and IgG2 and IgG4 proteins usually inhibited less than IgG1 and IgG3 proteins. Aggregation of the weakly inhibitory proteins with bis-diazotized benzidine increased their inhibitory effect. An IgG1 half-molecule with a deletion in the C3 domain was weakly inhibitory. Passage of lymphocytes through glass bead columns coated with IgG1 and IgG3 proteins removed K cell activity. In contrast, columns coated with IgG2 and IgG4 proteins, even when aggregated with BDB, failed to absorb K cells but removed significant numbers of SIg positive B lymphocytes. An enhancement of the antibody-dependent cytotoxicity was observed in 34% of the inhibition experiments in the presence of low concentrations of the weakly inhibitory proteins, usually IgG2 and IgG4. This enhancement occurred more frequently (53% of the experiments) with Fc fragments independent of the subclass. Moreover, addition of IgG2 and IgG4 but not IgG1 and IgG3 fragments induced a dose-dependent cytotoxicity to CRBC in the absence of anti-CRBC antibodies. These data indicate that IgG2 and IgG4 proteins have a lower affinity to K cells than IgG1 and IgG3 proteins and are compatible with an earlier hypothesis that proposes that more than one site on the Fc fragment can react with Fc receptors. The present results suggest in addition that there may be functionally different sites, one having a triggering function in K lymphocyte lysis that may be localized on the second constant domain and one being responsible for high affinity binding of IgG to cell receptors that is probably localized on the third constant domain.

Footnotes

¹ This study was performed during a leave of H. L. S. from the Department of Immunopathology and is publication No. 1145 from Scripps Clinic and Research Foundation. This work was supported by Grant 113-B75-10V from the Swedish Cancer Society and United States Public Health Service Grant AI-10734 from the National Institutes of Health.