Responses to multiple injections with alum alone compared to injections with alum adsorbed to proteins in mice

New effects and mechanisms of alum on innate immunity have emerged in recent years. A number of cellular and molecular mechanisms induced by aluminum adjuvant have been reported, while the role of NALP3 and inflammasome in the cellular pathway induced by alum is still controversial. The effect of injection of alum alone without vaccine antigen into human has not been reported so far. Recently, in a phase IIIa double-blinded placebo controlled clinical trial testing the therapeutic HBsAg-anti-HBs vaccine formulated with alum against chronic viral hepatitis B patients, the placebo group receiving alum only showed substantial therapeutic effects. To explore possible underlying therapeutic mechanisms, mice were treated either with multiple injections of alum alone or with alum adsorbed to proteins (HBsAg-anti-HBs). After 4 injections Gr1+/CD11b+ cells in the spleen were increased in both alum alone and alum adsorbed in proteins groups. Increased Gr1+/CD11b+ cells in spleens remained consistently high in the alum alone treated group, while Gr1+/CD11b+cells decreased in the alum adsorbed to proteins group after 6 injections. Both treatments triggered increased levels of TNF-alpha measured in the plasma, but only the alum alone treated mice showed increased levels of IL-10. Histology of the liver tissues revealed a higher number of spotty necrotic foci in the alum alone immunized group. Taken together, potent inflammatory responses were induced in the alum alone immunized mice, which suggests that the substantial therapeutic effects observed in chronic hepatitis B patients immunized with alum alone might be attributed to inflammatory responses.

► Multiple immunization with alum alone resulted in responses different from those immunized with alum adsorbed to proteins.
► Multiple injections with alum alone induced more potent inflammatory changes.
► Alum adsorbed to proteins induced up-regulation of TNF-α.
► Alum alone induced up-regulation of IL-10.