We also now formally demonstrate activation of the inflammasome by Borrelia. When spleen cells of mice lacking IL-1β were stimulated with Borrelia, IL-17 production was significantly diminished, which also raises the hypothesis that the IL-1β is also involved in induction
of Th17 cells by Borrelia spp. IL-17 selleckchem is associated with more severe disease progression in several autoimmune disorders, such as rheumatoid arthritis (RA) or multiple sclerosis 41. In patients diagnosed with RA, elevated levels of IL-17 were found in synovial fluid 42, 43. Since several clinical symptoms between RA and Lyme arthritis are similar, it has been proposed that IL-17 might be involved in the development of Lyme arthritis 10. In line with this hypothesis, it has been demonstrated that blockade of endogenous RG7420 purchase IL-17 in IFN-γ-deficient mice results in complete protection against development of arthritis after infection by Borrelia 44. These data
indicate that controlling the IL-17 response by IFN-γ plays an important role in chronic Lyme disease. IL-33 is a member of the IL-1 family and is mainly involved in induction of T-helper 2-like cytokines, such as IL-4 and IL-5 23. Although it was shown that IL-33 is cleaved by caspase-1, the activity of the mature protein has never been assessed. IL-33 can be secreted from cells after caspase-1 stimulation 45, very recent data suggest that IL-33 activity is independent of caspase-1 46, 47. More recently, it was shown that IL-33 can be functionally active and binds to its receptor ST2 without being cleaved by caspase-1, and that this cytokine is more related to IL-1α than to IL-1β or IL-18 48. It was also described that IL-33/ST2 binding results in the regulation of mainly Th2 responses, which is in line with our results. IL-33 seems not to be involved in either IL-17 or IFN-γ production by Borrelia spp. 23. In this study, we also demonstrate that IL-33 does not play a role in the regulation of pro-inflammatory
cytokines such as IL-1β and IL-6 induced after Borrelia exposure. This study demonstrates modulation of IFN-γ/IL-17 responses by Borrelia spp. through Farnesyltransferase inflammasome and caspase-1 activity. These findings are the first to demonstrate the existence of a counter-regulatory mechanism of Th1 versus Th17 cytokines during stimulation with Borrelia spp.. As shown in this study, IL-18 is crucial for the Borrelia-induced IFN-γ production, and IFN-γ has been suggested to be essential for induction of Th1 cells. Th1 cells drive cell-mediated immune responses and support the fight against invading pathogens. Induction of Th1 cells after recognition of Borrelia might be very important in the early immune response against spirochetes.