Figure 2

Pathogenic mechanisms of (a) Shigella flexneri and (b) Yersinia enterocolitica. (a) Shigella interacts preferentially with M cells in the colonic and rectal epithelia (upper panel), activates its T3SS and secretes IpaB and IpaC to form a pore inserted into the host cell membrane (lower panel). The bacterium then delivers effector proteins through the translocon to the eukaryotic cell cytoplasm. IpaC also activates RhoGTPases that, together with activated Src, recruit cortactin, involved in actin filament reorganization. VirA promotes microtubule destabilization, leading to activation of RhoGTPases. IpgD generates PI(5)P, thus promoting cell survival through Akt. IpaA binds to vinculin and induces actin depolymerization. Once inside the host cell, Shigella leaves the vacuole for the cytoplasm and escapes to neighboring cells (upper panel). (b) Yersinia adheres initially to M cells (upper panel) by means of its adhesins: invasin, which binds β₁ integrins directly; and YadA, which binds β₁ integrins indirectly through fibronectin (lower panel). The interactions between the adhesins and integrins cause bacterial internalization following activation of FAK, Rac-1 and Src, which are involved in subtle actin cytoskeletal rearrangements. The vacuole containing the bacterium is transported towards the basolateral side of the M cell, where it is expelled into the dome region of the FAE (upper panel). When Yersinia interacts with phagocyte integrins, the T3SS is activated and a set of effector proteins (Yops) are translocated into the phagocyte cytoplasm. Yops are involved in the antiphagocytic and anti-inflammatory mechanisms used by Yersinia that lead to the formation of microabcesses in the FAE.