The experiments presented in this paper demonstrate that the induction of tolerance on the one hand and the induction of delayed sensitivity on the other hand can be accomplished by administration of similar doses of azobenzene-arsonate conjugated to N-chloracetyl tyrosine (ABA-T) to guinea pigs with the determining factor being the absence or presence, respectively, of activating bacterial products in the adjuvant mixture used. Thus, complete, persistent ABA-T-specific T-cell tolerance can be induced in adult guinea pigs with 20 mug of ABA-T given intradermally in incomplete Freund's adjuvant (IFA) whereas this same dose of ABA-T induces ABA-specific immunity when administered in complete Freund's adjuvant. This tolerance was not reversible by administration of ABA-T and IFA in the presence of bacterial lipopolysaccharide, was generated before the formation of primed T cells, and persisted for at least 3 mo after initiation. Moreover, cell transfer studies performed herein demonstrate that the unresponsiveness resulting from administration of ABA-T in IFA reflects the activity of suppressor cells to induce and maintain a state of unresponsiveness could only be demonstrated in unprimed animals may indicate a severe limitation on the potential clinical usefulness of such an approach to regulation of the immune system.

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