Interleukin-17 is required for T helper 1 cell immunity and host resistance to the intracellular pathogen Francisella tularensis

The identification of a new T-cell subset referred to as T helper 17 (Th17) cells and its role in protective immunity against extracellular bacterial infections is well established. In contrast, initial studies suggested that the IL-23-IL-17 pathway was not required for protection against intracellular pathogens such as mycobacterial infections. However, recent studies demonstrate that Th17-IL-23 pathway may play a crucial role in protective immunity against other intracellular pathogens by regulating the innate and adaptive immune responses. The current outlook on the role of IL-23- IL-17 pathway in protective immunity to intracellular pathogens is discussed here.