The finding that significantly less IL-8 was released following apical or basolateral infection of Caco-2 cells with the wild-type strain compared with the effector delivery-defective mutant (Fig. 1B) supported the existence of an effector-dependent mechanism to antagonize flagellin-induced IL-8 secretion (Sharma et al., 2006). This evidence concerns the gene CXCL8 and infection.