Fig. 1.

Possible mechanisms of Fusobacterium nucleatum-induced β-defensin secretion and activation. F. nucleatum stimulates hBD-2 and hBD-3 secretions from epithelial cells. hBD-2 secretion induced by F. nucleatum is dependent on an outer membrane protein of the bacterium, namely Fusobacterium nucleatum-associated beta-defensin inducer (FAD)-1. F. nucleatum may, at least hypothetically, play a role in the activation of hBD-1 via its thioredoxin reductase, an enzyme which increases intracellularly as a response to oxidative stress.