MUCOSAL IMMUNOADJUVANT ACTIVITY OF LIPOSOMES - INDUCTION OF SYSTEMIC IGG AND SECRETORY IGA RESPONSES IN MICE BY INTRANASAL IMMUNIZATION WITH AN INFLUENZA SUBUNIT VACCINE AND COADMINISTERED LIPOSOMES

This paper reports on a novel immunonadjuvant activity of liposomes. A n influenza subunit preparation, containing the isolated viral surface antigens, was incorporated in 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. immuni zation with the antigen alone. In addition, the liposomal vaccine indu ced a secretory IgA (sIgA) response in the mucosa of the lungs and nas al cavity. Both serum IgG and sIgA responses persisted up to at least 21, weeks postimmmunization. Immune stimulation was ns observed with n egatively charged liposomes consisting of phosphatidylcholine (PC), ch olesterol and dicetylphosphate (DCP), but not with zwitterionic liposo mes, consisting of PC and cholesterol alone. Remarkably, for stimulati on of serum IgG responses and induction of an sIgA 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 sub unit antigen also resulted in immune stimulation, indicating that the liposomes did not exert their adjuvant effect by acting as a carrier f or the antigen. The liposomal vaccine conferred protection against inf ection. It is concluded that liposomes, administered i.n., provide a p romising adjuvant system for stimulation of antibody responses in gene ral, and mucosal sIgA responses in particular.