Characterization of Immunogenic Properties of Haptenated Liposomal Model Membranes in Mice. I. Thymus Independence of the Antigen

This paper describes a rather simple coupling method for tripeptide enlarged haptens to phosphatidylethanolamine (PE) and the incorporation of these conjugates into liposomal model membranes (haptenated liposomes). These haptenated liposomes evoke a hapten-specific humoral immune response in mice. The magnitude of the response as measured by the appearance of direct plaque forming cells in the spleen is dependent on the route of immunization and the dose and epitope density of the hapten-PE derivatives. It was not possible to evoke an IgG response after either primary or secondary immunization with haptenated liposomes (as measured by the production of indirect plaques or mercaptoethanol-resistant antibody). These data, in addition to the observations that mice depleted of, or deficient in thymus-derived (T) lymphocytes respond to haptenated liposomes, indicate that these haptenated liposomes are T-cell independent antigens.