[Immunopathogenesis of Legionnaires' disease]

Legionella pneumophila, the causative agent of Legionnaires' disease, is a facultative intracellular pathogen of alveolar macrophages, alveolar epithelial cells and, blood monocytes. Infection begins with the inhalation of the L.pneumophila. Once the bacteria reach to alveolar spaces, they come in contact with the alveolar macrophages, phagocyted and the macrophage takes the bacteria into a phagosome. Inside the cell, Legionella inhibits the lysosome-phagosome fusion, resulting in multiplication and lysis of the cell. The newly formed bacteria infect the other cells. In-vitro studies have shown that the presence of antibody and complement do not enhance intracellular killing. Cellular immunity is more important than humoral immunity for resolution of Legionella infections. In this review article, immunopathogenesis of Legionella infections have been discussed under the light of literature.