Effect of the Degree of Phosphate Substitution in Aluminum Hydroxide Adjuvant on the Adsorption of Phosphorylated Proteins

Aluminum hydroxide adjuvant was pretreated with six concentrations of potassium dihydrogen phosphate to produce a series of adjuvants with various degrees of phosphate substitution for surface hydroxyl. The adsorption of three phosphorylated proteins (alpha casein, dephosphorylated alpha casein, and ovalbumin) by the phosphate-treated aluminum hydroxide adjuvants was studied. The phosphorylated proteins were adsorbed by ligand exchange of phosphate for hydroxyl even when an electrostatic repulsive force was present. However, the extent (adsorptive capacity) and strength (adsorptive coefficient) of adsorption was inversely related to the degree of phosphate substitution of the aluminum hydroxide adjuvant. Exposure of vaccines containing aluminum hydroxide adjuvant and phosphorylated antigens to phosphate ion in the formulation or during manufacture should be minimized to produce maximum adsorption of the antigen.