Suppression of Reaginic Antibody Formation

From the study of the effect of epitope density on the immunogenicity of haptenated ovalbumin (DNP-OA) it was concluded that the lightly haptenated conjugate, DNP0.5-OA, induced, on the one hand, only low titers of anti-DNP hemagglutinating antibody and no reaginic antibodies to the hapten and, on the other, high reaginic and high hemagglutinating antibody responses to the carrier. The conjugate with a slightly higher degree of haptenation, i.e., DNP2.3-OA, induced both reaginic and hemagglutinating antibodies to both the hapten and the carrier. By contrast, the heavily haptenated conjugate, DNP20-OA, elicited reaginic and hemagglutinating antibodies only against the hapten but not against the carrier. Specific suppression of anti-hapten reaginic antibody formation had been achieved by treatment of mice with a tolerogen consisting of the hapten (DNP) conjugated covalently to isologous γ globulins (MγG). The epitope density of the DNPx-MγG conjugates was shown to play a dominant role in determining whether or not the conjugate was tolerogenic. Thus, lightly haptenated conjugates (DNP0.5-MγG, DNP1.3-MγG or DNP1.9-MγG) were not tolerogenic, moderately haptenated conjugates (DNP4.2-MγG, DNP8-MγG, and DNP14-MγG) were tolerogenic, and heavily haptenated conjugates (DNP32-MγG and DNP53-MγG) were immunogenic, being capable of priming the recipients for the DNP hapten. Further evidence for the nonimmunogenicity of DNP8-MγG conjugate was inferred from its rate of clearance in tolerized and normal mice. Thus, the half-life of 125I-labeled DNP8-MγG in circulation was not significantly different for normal and tolerized mice; it was 3.7 and 3.5 days, respectively, which is within the range of data reported for clearance of normal MγG. These results suggest that DNP8-MγG was catabolized at a rate similar to that of nonconjugated, isologous MγG. Moreover, there was no significant difference in the localization of DNP8-MγG in identical organs (spleen, thymus, kidney, and liver) of normal and tolerized mice. All the multivalent DNPx-MγG conjugates were shown to be able to elicit passive cutaneous anaphylaxis (PCA) reaction on i.v. Challenge of rats which had been pre-sensitized i.d. with anti-DNP reaginic antibodies.