Enhancement by lipid A of mucosal immunogenicity of liposome-associated cholera toxin.

Two methods that might enhance the mucosal immunogenicity of a protein antigen, cholera toxin (CT), were studied in rats: association of CT with liposomes, and coadministration of CT with lipid A. Enteric priming by CT was not enhanced when the antigen was trapped within liposomes or bound to their surface via GM1 ganglioside, nor was it improved when CT was mixed with lipid A or with liposomes containing lipid A. However, lipid A did enhance priming by liposome-associated CT when the lipid A was incorporated into CT-bearing liposomes. It is concluded that lipid A can act as an adjuvant for a local IgA response to a mucosally applied antigen, at least when lipid A and the antigen are associated on a liposome carrier.