Immunogenicity of hapten-carrier conjugates associated with liposomes

Immunogenicity of liposome-entrapped hapten-carrier conjugates was studied in guinea pigs. Animals immunized intravenously with a subimmunogenic dose of a hapten-carrier complex entrapped in liposomes exhibited cutaneous anaphylactic reactions to the hapten, even when the liposomes were treated with trypsin, but not delayed hypersensitivity (DH) reactions to the carrier. Animals immunized with a mixture of empty liposomes and antigen showed anaphylactic reactions to the hapten that appeared to be elicited by antigen adsorbed on the outer membrane of liposomes. The induction of anaphylaxis to the hapten by liposome-associated antigen was not due to an adjuvant property of liposomes. DH reactions to the carrier after injection of a liposome-entrapped subimmunogenic dose of a hapten-carrier conjugate could be observed only after activation of macrophages by Bacillus Calmette-Guérin.