Immunogenicity of liposomal model membranes in mice: dependence on phospholipid composition.

This investigation demonstrated that antigenic expression in liposomal model membranes may be markedly influenced by phospholipid composition. Incorporation of dinitrophenylaminocaproylphosphatidylethanolamine (Dnp-Cap-PE) into egg lecithin/cholesterol/dicetylphosphate bilayers did not significantly enhance the response of AKR mice to this synthetic amphipathic antigen. In contrast, the immunogenicity of Dnp-Cap-PE was increased (as measured by either plaque-forming cell frequency of hemagglutination titer) after its insertion into liposomes prepared with beef sphingomyelin instead of egg lecithin. We also show that the response to the Dnp-Cap determinant can be stimulated by the presence of lipid A in the same bilayers without altering the relative immunogenic potency of the sphingomyelin and lecithin liposomes; similarly, incorporation of this mitogen into sphingomyelin liposomes produced a greater polyclonal (nonspecific) response. The response to Dnp-Cap-PE-sensitized liposomes (with or without lipid A) prepared with a series of synthetic phosphatidylcholines (distearoyl-, dipalmitoyl-, dimyristoyl-, dilauroyl-, dioleoyl-) suggests a direct correlation between liposomal immunogenicity and transition temperature of the phospholipid.