Interferon-gamma inductive effect of liposomes as an immunoadjuvant.

Adjuvant effect of liposomes was compared to that of aluminium hydroxide (Alum) using ovalbumin (OVA) as a model antigen, and the difference in adjuvanticity of liposomes from Alum has been evaluated on the basis of cytokine production. Both adjuvants enhanced the IgG levels, but a remarkable difference was observed in the production of IgG subclass; Alum enhanced IgG1 levels, and liposomes enhanced IgG2a, IG2b, and IG3 levels. Further, Alum enhanced antigen-specific IgE levels, whereas liposomes did not. To clarify the difference in adjuvant effect of these adjuvants, secretion of cytokines, especially interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) which regulate IgE production, was estimated ex vivo. Overnight culture of splenic cells obtained from mice immunized with liposomes encapsulating OVA elicits IFN-gamma secretion, but not IL-4 secretion. On the other hand, the production of both cytokines was elevated by the immunization with OVA-Alum complex. The results indicate that the difference of adjuvant activity between liposomes and Alum may come from the difference in the secretion of IL-4 and that, consequently, a different class of antibody response is developed. More importantly, negatively charged liposomes containing phosphatidylserine remarkably promoted IFN-gamma secretion compared to neutral liposomes.