Relationship between the degree of antigen adsorption in the vaccine or in interstitial fluid and the ensuing immune response

The adsorption of ovalbumin, alpha casein and dephosphorylated alpha casein on untreated and phosphate-treated aluminum hydroxide adjuvants was studied. The adsorption of alpha casein on aluminum phosphate adjuvant was also studied. The adsorption of ovalbumin on the aluminum-containing adjuvants was attributed to electrostatic attraction as well as covalent bonding. Alpha casein is believed to covalently bind to the aluminum-containing adjuvants via its 8 phosphate monoester groups. All the proteins showed maximum adsorption on untreated aluminum hydroxide adjuvant and the adsorption decreased with increasing phosphate substitution on the adjuvant surface. Desorption studies of ovalbumin from aluminum-containing adjuvants in a 5 mM phosphate solution revealed that ovalbumin underwent rapid desorption from all of the adjuvants. Rapid desorption of dephosphorylated alpha casein from aluminum containing adjuvants was noticed upon dilution with sheep interstitial fluid. Remarkably, alpha casein did not undergo significant desorption from any of the adjuvants after a 24-hour exposure to interstitial fluid. Dissolution studies in interstitial fluid of aluminum from aluminum hydroxide adjuvant and from model vaccines in which ovalbumin, alpha casein, dephosphorylated alpha casein and myoglobin were adsorbed onto aluminum hydroxide adjuvant revealed that aluminum dissolution occurred from all the systems although protein adsorption decreased the rate of dissolution. The observation that alpha casein did not desorb from aluminum hydroxide adjuvant even as the adjuvant underwent dissolution in interstitial fluid contradicted the previous assumption that antigens are desorbed as aluminum-containing adjuvants dissolve in vivo. Animal studies with ovalbumin, alpha casein and dephosphorylated alpha casein with untreated and phosphate-treated aluminum hydroxide adjuvants revealed that aluminum-containing adjuvants potentiated the immune response to the antigens. The potentiation of the immune response to ovalbumin and dephosphorylated alpha casein that were adsorbed to varying degrees in the vaccine but showed rapid desorption in interstitial fluid questioned the depot mechanism which requires slow desorption of the antigen to provide a long term exposure to the antigen. Aluminum hydroxide adjuvant also enhanced the immune response to alpha casein that was completely adsorbed in the vaccine and in interstitial fluid. This showed that the body is capable of producing antibodies to an antigen that does not desorb from the aluminum-containing adjuvant after administration. Thus, in the presence of aluminum-containing adjuvants, a potentiation of the immune response occurred whether the antigen was desorbed quickly or did not desorb in interstitial fluid