CONTRIBUTION OF ELECTROSTATIC AND HYDROPHOBIC INTERACTIONS TO THE ADSORPTION OF PROTEINS BY ALUMINUM-CONTAINING ADJUVANTS

The effect of ionic strength and ethylene glycol on the adsorption of bovine serum albumin (BSA) or lysozyme by a commercial aluminium hydro xide or aluminium phosphate adjuvant was studied at pH 7.4 and 25 degr ees C. The adsorption of BSA by aluminium hydroxide adjuvant and lysoz yme by aluminium phosphate adjuvant was found to be inversely related to ionic strength, This indicates that electrostatic attractive forces contribute to adsorption. The adsorption of lysozyme by aluminium pho sphate adjuvant was reduced by the addition of ethylene glycol. Howeve r, no change in the adsorption of BSA by aluminium hydroxide adjuvant was noted when up to 40% ethylene glycol was present. This behaviour i ndicates that hydrophobic forces contribute to the adsorption of lysoz yme but not of BSA. However, virtually no adsorption was observed when the protein and the adjuvant had the same surface charge. Thus, attra ctive forces may not be sufficient to produce adsorption of an antigen by an aluminium-containing adjuvant if electrostatic repulsive forces are present.