Mechanism of action of clinically approved adjuvants.

Aluminum-containing adjuvants continue to be the most widely used adjuvants for human use. In the last year a major breakthrough has been the realization that alum adjuvant triggers an ancient pathway of innate recognition of crystals in monocytes and triggers them to become immunogenic dendritic cells, nature's adjuvant. This recognition can occur directly, via the triggering of the NALP3 inflammasome by alum crystals, or indirectly through release of the endogenous danger signal uric acid. It is also clear now that adjuvants trigger the stromal cells at the site of injection, leading to the necessary chemokines that attract the innate immune cells to the site of injection. How exactly these pathways interact remains to be determined.