Tracing Aluminium-based Adjuvants : Their Interactions with Immune Competent Cells and their Effect on Mitochondrial Activity

Background:Studies revealing the immune stimulatory properties of aluminium-based adjuvants (ABAs) have been impaired by the absence ofsimple and reliable methods of tracing the adjuvants and their effect on biochemical processes upon endocytosis.Objective:To verify that labelling of ABAs with lumogallion doesn’t affect the physicochemical properties of the adjuvant; tracing cellularinteraction with aluminium adjuvants; explore their effect on metabolic activity upon endocytosis.Methods:Physicochemical characterization by Z-potential and size distribution of ABAs labelled with lumogallion. Cellular interactions withABAs by flow cytometry and confocal microscopy. Metabolic activity explored by measuring transformation of tetrazolium intoformazan.Results:No or minor change of zeta potential and average particle size of lumogallion labelled aluminium oxyhydroxide, AlO(OH) andaluminium hydroxyphosphate, Al(OH)x(PO4)y. Both phagocytosing and non-phagocytosing leukocytes became associated withABAs at concentrations expected after in vivo administration of a vaccine. The ABAs were relatively toxic, affecting bothlymphocytes and monocytes, and Al(OH)x(PO4)y was more toxic than AlO(OH). Endocytosed aluminium adjuvant particles werenot secreted from the cells and remained intracellular throughout several cell divisions. The presence of ABAs increased themitochondrial activity of the monocytic cell line THP-1 and peripheral monocytes, as based on the transformation of tetrazolium intoformazan.Conclusion:Lumogallion labelled ABAs is a valuable tool tracing interactions between ABAs and cells. Labelled ABAs can be tracedintracellularly and ABAs are likely to remain intracellular for a long period of time. Intracellular ABAs increase the mitochondrialactivity and the presence of intracellular Al ions is suggested to cause an increased mitochondrial activity.Keywords: Aluminium based adjuvant, Lumogallion, Mitochondrial activity, MTT assay, Phagocytosis, ABAS, Zeolites