Effect of protein adsorption on the surface charge characteristics of aluminium-containing adjuvants

The effect of adsorbing two model proteins, bovine serum albumin and lysozyme, on the point of zero charge of aluminium-containing vaccine adjuvants was studied. At physiological pH, the adsorption of the negatively charged albumin (isoelectric point = 5.0) by aluminium hydroxide adjuvant (point of zero charge = 11.1) resulted in a decrease in the point of zero charge. In contrast, the adsorption of positively charged lysozyme (isoelectric point = 9.6) by the negatively charged aluminium phosphate adjuvant (point of zero charge = 5.0) resulted in an increase in the point of zero charge. The surface charge characteristics of the aluminium-containing adjuvant dominated at low protein coverage. In contrast, the surface charge characteristics of the adsorbed protein dominated at high protein coverage. Therefore, the physicochemical properties of the antigen-adjuvant complex and not the adjuvant alone should be considered during vaccine preparation.