Yersinia bacteria cause disease through several virulence factors. They produce a toxin called Yersinia outer membrane proteins (Yops) that are injected into host cells and suppress the immune response. Yersinia also uses an invasin protein to enter nonphagocytic cells and avoids destruction by phagocytes. The combination of these virulence factors allows Yersinia to evade the immune system and cause illnesses like plague, yersiniosis, and pseudotuberculosis.