Delayed hypersensitivity. IV. Hapten-specific delayed reactions; interaction of immune serum and sensitized cells.

Delayed hypersensitivity reactions to hapten-protein antigens are largely conjugate specific. Concurrent elicitation of related or unrelated immediate reactions at challenge sites, however, resulted in hapten-specific 24-hr reactions in passively and actively immunized guinea pigs. Challenge with a 10-fold increase in the concentration of antigen also resulted in hapten-specific 24-hr transfer reactions. Hapten-specific reactions were elicited at sites prepared by injection of normal guinea pig serum. Increased antigen concentration and nonspecific infiltration of mononuclear cells at prepared skin sites are possible mechanisms underlying these hapten-specific delayed reactions.