Mechanism of delayed reactions.

Arsanilic acid conjugates of polymers of L-typrosine, glutamic acid, and alanine are immunogenic and can elicit hapten-specific, delayed-hypersensitivity reactions in sensitized guinea pigs. Conjugates of the D-amino acid polymers are neither immunogenic nor capable of eliciting delayed reactions. Mixtures of small amounts of conjugates capable of eliciting a delayed reaction with larger amounts of D-amino acid polymer conjugates produce only small delayed reactions. I suggest that the delayed reaction is an active response requiring the continued participation of immunogenic material in sensitized animals; it is not the reaction of preformed antibody-like material with the antigenic determinant.