Termination of acquired immunological tolerance to protein antigens following immunization with altered protein antigens.

Acquired tolerance to BSA in rabbits was terminated following the injection of certain preparations of altered BSA. Injections of Freund's adjuvant containing BSA complexed to anti-BSA, heat-denatured BSA, acetyl-BSA, picryl-BSA, or arsanil-BSA failed to terminate the tolerant state. Except in an occasional tolerant rabbit, injections of these preparations failed to cause the production of precipitating antibody to the altered preparation. Similar results were obtained following injections of alum-precipitated preparations of pepsin-degraded BSA, acetyl-BSA, and picryl-BSA. Injections of Freund's adjuvant containing sulfanil-BSA terminated the tolerant state, but only small amounts of non-precipitating anti-BSA were produced. Injections of Freund's adjuvant containing picryl-acetyl-BSA terminated the tolerant state in two of six rabbits, but again, only small amounts of non-precipitating anti-BSA were produced. Injections of an alum-precipitated preparation of picryl-acetyl-BSA failed to terminate the tolerant state. On the other hand, injections of Freund's adjuvant containing arsanil-sulfanil-BSA terminated the tolerant state in eleven of eleven rabbits and caused the production of precipitating anti-BSA in all nine of the rabbits tested. The tolerant state was terminated also in six of six rabbits injected with an alum-precipitated preparation of arsanil-sulfanil-BSA. Only one of these rabbits produced precipitating anti-BSA. In addition, the injection of BGG-tolerant rabbits with arsanil-BGG, sulfanil-BGG, or arsanil-sulfanil-BGG terminated the tolerant state. These results were discussed in relation to both the clonal selection theory of antibody production and autoimmunity.