Rijksuniversiteit Groningen Mucosal Immunoadjuvant Activity of Liposomes

This paper reports on a novel immunoadjuvant activity of liposomes. An influenza subunit preparation, containing the isolated viral surface antigens, was incorporated a liposomal formulation. Administration of this vaccine to mice via the intranasal (i.n.) route resulted in a stimulated serum IgG response relative to the response to i.n. immunization with the antigen alone. In addition, the liposomal vaccine induced a secretory IgA (s-IgA) response in the mucosa of the lungs and nasal cavity. Both serum IgG and s-IgA responses persisted up to at least 21 weeks post-immunization. Immune stimulation was observed with negatively charged liposomes consisting of phosphatidylcholine (PC), cholesterol, and dicetylphosphate (DCP), but not with zwitterionic liposomes, consisting of PC and cholesterol alone. Remarkably, for stimulation of serum IgG responses and induction of an s-IgA response, liposomes could be simply mixed with the antigen. Moreover, i.n. administration of empty liposomes up to 48 h prior to i.n. immunization with the subunit antigen also resulted in immune stimulation, indicating that the liposomes did not exert their adjuvant effect by acting as a carrier for the antigen. The liposomal vaccine conferred protection against infection. It is concluded that liposomes, administered i.n., provide a promising adjuvant system for stimulation of antibody responses in general, and mucosal s-IgA responses in particular.