Bacterial flagellin—a potent immunomodulatory agent

Flagellin is a subunit protein of the flagellum, a whip-like appendage that enables bacterial motility. Traditionally, flagellin was viewed as a virulence factor that contributes to the adhesion and invasion of host cells, but now it has emerged as a potent immune activator, shaping both the innate and adaptive arms of immunity during microbial infections. In this review, we summarize our understanding of bacterial flagellin and host immune system interactions and the role flagellin as an adjuvant, anti-tumor and radioprotective agent, and we address important areas of future research interests. Flagellin, a protein in the whip-like flagella powering bacterial motion, can activate different parts of the immune system in several ways. John Hwa Lee and a colleague at Chonbuk National University in South Korea, with co-workers at the University of Toledo in USA, reviewed current understanding of the interactions between flagellin and host immune systems. A range of biochemical effects allows flagellin to activate both non-specific "innate" immunity and the "adaptive" immune system that responds to and remembers specific infections. Flagellin can act as a molecule that enhances the immune response, and as an anti-tumor agent, and can offer protection against the damaging effects of exposure to radiation. These activities suggest that the medical potential of flagellin should be explored further, especially in cancer treatment and the development of new vaccines.