Infiltrating PMN destroy the integrity of the epithelial lining, thus enabling more luminal bacteria to reach the submucosa without the need of M cells (214, 215) (Fig. (Fig.1).1). In addition, S. flexneri seems to weaken the sealing of the EC tight junctions by altering the tight-junction protein composition (242). Thus, macrophage killing, destruction of the epithelial layer, and the massive influx of PMN exacerbate the bacterial infection and tissue lesion. These processes are essential for the development of diarrhea and the characteristic pathology of shigellosis. Ultimately, however, the PMN recruited to the site of infection entrap and kill the bacteria, thereby resolving the infection (29, 158, 342). In addition, IFN-γ plays a crucial role for the innate resistance to S. flexneri infection (328). The activation of macrophages and their protection from S. flexneri-triggered cell death likely account for the effects of IFN-γ at least partially (108).