Purdue researcher Stanley Hem has found that aluminum hydroxide, a small particle used to carry antigens into the body to boost an immune response, begins to dissolve in the muscle immediately after an injection and is eliminated from the body hundreds of times faster than presumed. The most popular theory was that it remained in the muscle for months while the body produced antibodies in response to the antigens carried on its surface. The study raises new questions about the mechanism by which aluminum hydroxide works, Hem says. The findings will appear in the September issue of the British scientific journal Vaccine. During the 1930s, researchers discovered that using aluminum hydroxide to carry antigens into the body resulted in a greater production of antibodies than could be produced by the antigen alone.
Antibodies are proteins made by the immune system to fight off foreign substances.
Since 1934, aluminum hydroxide has been used as an adjuvant to boost the immune response from vaccines. Currently, it is the only adjuvant approved by the Food and Drug Administration for use in human vaccines. The FDA limits the dosage to 0.85 milligrams per vaccine to minimize exposure to aluminum. Though scientists have puzzled over the mechanism by which aluminum hydroxide increases the production of antibodies, the tiny amounts of the substance used in vaccines made it impossible to track or analyze it once it was injected into the body, Hem says. Though this explanation was generally accepted, Hem says he questioned how aluminum particles could stay in the muscle for great lengths of time.