Legionella pneumophila is a facultative intracellular pathogen that can replicate within phagocytic host cells such as protozoa and macrophages. Evasion of phagocytic killing is mediated by the type IV Dot/Icm secretion system, which exports bacterial effectors that modulate biogenesis of the phagosome to evade endocytic fusion and also to intercept vesicles derived from the endoplasmic reticulum. Bacterial replication is associated with activation of caspase-3 in infected macrophages and is culminated in apoptosis and pore formation-mediated cytolysis of the host.