Hypersensitivity: specific immunologic suppression of the delayed type.

Delayed-type cutaneous hypersensitivity to sheep erythrocytes was induced in rats by intradermal injection of the antigen mixed with Freund's adjuvant; hypersensitivity was sustained by weekly injections. Either passive immunization with rat antiserum to sheep erythrocytes or intravenous injection of sheep erythrocytes partially suppressed induction of hypersensitivity; these procedures used together specifically and completely suppressed induction of hypersensitivity. Complete suppression was sustained by antigen given intravenously before each weekly injection of the mixture of antigen and adjuvant. These findings provide the rational basis of a simple method for prolonging survival of allografts with only the biological agents, antigen and antibody, of the immunological response.