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Effects of Antigen Density and Non-Complement Fixing Antibody on Cytolysis by Alloantisera¹

Department of Pathology, New York University School of Medicine, New York, New York 10016

Abstract

Murine alloantisera were prepared against a variety of isoantigens including H2.25, TL, and LyA₂. These antisera were cytotoxic for thymocytes and tumor cells. Anti-TL antisera obtained early in the immunization yielded titration curves in which antibody killed more than 90% of the target cells and which gave sharp end points and relatively high titers. Antisera obtained later during immunization frequently gave distinct "prozones", failed to destroy all of the target cells, and gave less well defined end points. An immunoglobulin fraction presumably containing non-complement-fixing (NCF) antibody was purified from this late antiserum. This fraction was capable of reducing the cytotoxic efficiency ofthe early antisera. These effects were also duplicated when early antisera were tested against cells whose antigenic content had been reduced on a genetic basis. Such cells were markedly less susceptible to cytolysis than were cells with a full antigenic content. This resistance could in part be abrogated by an increased antibody and/or increased complement concentration. It was concluded that susceptibility to cytotoxic antibody is strongly influenced by antigen density and that NCF antibodies exert their effects on cytotoxin determinations by reducing the effective concentration of antigen on the target cell.

Footnotes

¹ This work was supported by United States Public Health Service Grant AI-11326 and Career Development Award HD 34968.