Biological effects of aluminum adjuvants: I. Detoxification of endotoxin. II. The relationship between antigen adsorption and the immune response

Langmuir adsorption isotherms of endotoxin and aluminum adjuvants revealed that aluminum hydroxide adjuvant has a greater adsorption capacity and adsorption coefficient than aluminum phosphate adjuvant. The difference in endotoxin adsorption was related to two adsorption mechanisms: electrostatic attraction and covalent bonding. The iep of endotoxin is 2. An electrostatic attractive force is present with aluminum hydroxide adjuvant (iep = 11.7). An electrostatic repulsive force operates with aluminum phosphate adjuvant (iep = 4.6). Endotoxin contains two phosphate groups in the lipid A portion. Covalent bonding occurs with surface aluminum in aluminum hydroxide adjuvant but is inhibited by surface phosphate in aluminum phosphate adjuvant. The endotoxin adsorbed by aluminum hydroxide adjuvant was not desorbed by interstitial anions (5 mM phosphate or 2.7 mEq/L citrate) or interstitial proteins (25 mg/ml albumin). TNF-α and IL-6 were observed in the group of rats received an endotoxin solution or endotoxin and aluminum phosphate adjuvant but not in the group received endotoxin and aluminum hydroxide adjuvant. Aluminum hydroxide adjuvant could completely protect animal from endotoxin. The protective effect is attributed to the irreversible adsorption of endotoxin by aluminum hydroxide adjuvant in vaccine as well as in interstitial fluid. Exposing to interstitial fluid caused substantial change in lysozyme adsorption by aluminum adjuvants. Fibrinogen, an interstitial protein, was used to block the lysozyme adsorption on aluminum phosphate adjuvant. Less than 5% of lysozyme was adsorbed both in vaccine and in interstitial fluid. Without the blocking 35% of lysozyme was adsorbed on aluminum phosphate adjuvant. No significant anti-lysozyme IgG2a production and high IgG 1 titer were observed in BLAB/c mice after subcutaneous administration of lysozyme and the aluminum adjuvants. The geometric mean IgG1 titers of the group of mice which received lysozyme with aluminum phosphate adjuvant or with fibrinogen-blocked aluminum phosphate adjuvant were not significantly different but four times greater than that received lysozyme solution alone. This study shows that lysozyme adsorption was not essential for the aluminum adjuvants to potentiate the immune response. It is likely that aluminum adjuvant stimulates the immune response by local irritation and antibody production is stimulated when antigen is at the same site