Innate immunity to Legionella and toll-like receptors - review.

Legionella is a parasite of eukaryotic cells, able to survive and replicate in a wide range of protozoan hosts. It can also infect humans as an opportunistic pathogen, primarily by interaction with alveolar macrophages. These bacteria can cause life-threatening pneumonia, especially in immunocompromised individuals. However, most infections triggered by Legionella are cleared by an efficient host immune system. The protective immune responses against Legionella are complex and multifaceted, involving many components of the immune system. Recognition of such components as LPS, flagellum, and peptidoglycan of L. pneumophila by the TLRs, which orchestrates the innate immune responses to Legionella, lays an important role in activation of monocytes and alveolar macrophages and, thus, in inhibition of intracellular proliferation of bacteria. MyD88-dependent signaling pathways are important for host protection against Legionella.