A number of azobenzenearsonate (ABA) conjugates have been prepared and tested for ability to react with antibody, to sensitize for hapten-specific delayed hypersensitivity and to induce hapten-specific unresponsiveness. All conjugates tested by in vitro or in vivo methods show a capacity to react with preformed antibody. Conjugates of L-amino acid polymers are immunogenic and induce tolerance. Conjugates of D-amino acid polymers or conjugates with high density of ABA groups are nonimmunogenic and fail to induce tolerance.

Since paired D- and L-polymer conjugates react comparably with preformed antibody but differ markedly in tolerance induction, it is argued that combination with an antibody-like receptor molecule on the surface of an immune-competent cell is not a sufficient condition for tolerance. The lack of effectiveness of sterically crowded conjugates as well as D-polymer conjugates argues for a preliminary biologic "processing" of antigen necessary for induction of immunity or tolerance. Such a processing event might well involve enzymatic attack on the antigen.

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