Treatment of adult mice with dinitrophenyl (DNP) bound to isogeneic serum resulted in a specific inability to respond to DNP after challenge with DNP-keyhole limpet hemocyanin (KLH) in complete Freund's adjuvant. The unresponsiveness to the hapten had all the characteristics of immunologic tolerance: it had a definite induction time; it was transient but could be maintained by additional injections of the tolerogen; it was antigen specific and dose dependent. In addition, the induction of tolerance to DNP is dependent on the nature of the carrier.

Two main conclusions can be drawn from these data: DNP conjugates of three homopolymers of lysine were found to be nonimmunogenic in mice, yet tolerogenic. Thus, antigenicity is not necessary to induce tolerance.

Among the various carriers tested, isogeneic 7S immunoglobulin (IgG) was found to be the most effective to induce and maintain tolerance to the hapten. This suggests that IgG may have a function other than its usual role as an immunoglobulin.

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