IL-17 and Th17 Cells in Chlamydiae Infection.

Chlamydia is a genus of intracellular parasitic microorganisms with a unique developmental cycle that is widely distributed and can cause various human and animal diseases. T helper 17 (Th17) cells are a distinct subpopulation of Th cells with a unique transcriptional profile (STAT3, RORγt and RORα), a pattern of cytokine production (IL-17 family, IL-21, IL-22) and specific cytokines required for differentiation (IL-6, TGF-β, IL-21 and IL-23). Results from mouse models of infection and human epidemiologic studies indicate that Th17 cells may be vital in modulating innate and adaptive immune responses for protective immunity against chlamydia and are associated with the progression of inflammatory diseases in various organs and tissues. This article reviews the differentiation of Th17 cells during Chlamydia infection, the host defence mechanisms involved, and their critical role in the pathogenesis of inflammation and autoimmune damage, with the aim of informing the development of safe and effective Th17 cell-based vaccines against Chlamydia.