Enhancement of immunogenicity by incorporation of lipid A into liposomal model membranes and its application to membrane-associated antigens.

Incorporation of lipid A into liposomes markedly enhances the plaque-forming cell (PFC responses against model membranes that are sensitized with synthetic amphipathic antigens 2,4-dinitrophenyl-6-N-aminocaproyldipalmytoylphosphatidylethanolamine (DNP-Cap-DPPE) and fluorescein thiocarbamyldipalmytoylphosphatidylethanolamine (FI-DPPE). The enhancing effect was pronounced only when lipid A and haptenic determinants were presented on the same liposome. Lipid A was incorporated into heterologous erythrocytes and syngeneic tumour cells. Significant and selective increase of in-vitro PFC responses was observed against heterologous erythrocytes, and immunization of C578L/6 mice with lipid A treated X-irradiated tumour cells (EL-4) markedly prolonged the survival of mice after challenge with homologous viable tumour cells. These data suggest that passively incorporated lipid A will be an effective method for selectively augmenting antibody formation against membrane-associated antigens. [ABSTRACT FROM AUTHOR]