Neutrophils infiltrate the site of infection and play critical roles in host defense, especially against extracellular bacteria. In the present study, we found a rapid and transient production of IL-17 after i.p. infection with Escherichia coli, preceding the influx of neutrophils. Neutralization of IL-17 resulted in a reduced infiltration of neutrophils and an impaired bacterial clearance. Ex vivo intracellular cytokine flow cytometric analysis revealed that γδ T cell population was the major source of IL-17. Mice depleted of γδ T cells by mAb treatment or mice genetically lacking Vδ1 showed diminished IL-17 production and reduced neutrophil infiltration after E. coli infection, indicating an importance of Vδ1+ γδ T cells as the source of IL-17. It was further revealed that γδ T cells in the peritoneal cavity of naive mice produced IL-17 in response to IL-23, which was induced rapidly after E. coli infection in a TLR4 signaling-dependent manner. Thus, although γδ T cells are generally regarded as a part of early induced immune responses, which bridge innate and adaptive immune responses, our study demonstrated a novel role of γδ T cells as a first line of host defense controlling neutrophil-mediated innate immune responses.

We previously reported that resident γδ T cells in the peritoneal cavity rapidly produced IL-17 in response to Escherichia coli infection to mobilize neutrophils. We found in this study that the IL-17-producing γδ T cells did not produce IFN-γ or IL-4, similar to Th17 cells. IL-17-producing γδ T cells specifically express CD25 but not CD122, whereas CD122+ γδ T cells produced IFN-γ. IL-17-producing γδ T cells were decreased but still present in IL-2- or CD25-deficient mice, suggesting a role of IL-2 for their maintenance. IFN-γ-producing CD122+ γδ T cells were selectively decreased in IL-15-deficient mice. Surprisingly, IL-17-producing γδ T cells were already detected in the thymus, although CD25 was not expressed on the intrathymic IL-17-producing γδ T cells. The number of thymic IL-17-producing γδ T cells was peaked at perinatal period and decreased thereafter, coincided with the developmental kinetics of Vγ6+Vδ1+ γδ T cells. The number of IL-17-producing γδ T cells was decreased in fetal thymus of Vδ1-deficient mice, whereas Vγ5+ fetal thymocytes in normal mice did not produce IL-17. Thus, it was revealed that the fetal thymus-derived Vγ6+Vδ1+ T cells functionally differentiate to produce IL-17 within thymus and thereafter express CD25 to be maintained in the periphery.

IntroductionConventional TCR ␣␤ cells are exported from the thymus as naive T cells. After activation by exposure to their cognate antigens in the periphery, naive CD4 ϩ ␣␤ T cells differentiate into different helper T-cell lineages such as Th1, Th2, and Th17 cells, depending on the cytokine milieu, which induce different combinations of transcription factors. STAT3, ROR␥t, and ROR␣, which are induced by combined signals from TGF␤ and IL-6 receptors, play important roles in the differentiation of Th17 cells by binding to the promoter or the enhancer region of the IL17 gene. 1-3 STAT3 also inhibits the expression of Foxp3, which suppresses the functions of ROR␥t. 4 In addition to Th17 cells, several subsets of T cells produce IL-17. These include T cells lacking CD4 and CD8, CD8 ϩ T cells, invariant natural killer T cells (NKT cells), and TCR ␥␦ T cells. [5][6][7][8] There is accumulating evidence that TCR ␥␦ T cells could be the major source of IL-17 in various murine models of infection such as Mycobacterium tuberculosis, Escherichia coli, and Listeria monocytogenes. 9 IL-17-producing ␥␦ T cells are also involved in the pathogenesis of autoimmune diseases such as experimental allergic encephalomyelitis, collagen-induced arthritis, chronic granulomatous disease, and ischemic brain injury. 10 Interestingly, even freshly isolated ␥␦ T cells from the thymus produce IL-17 in response to phorbol myristate acetate (PMA) and ionomycin stimulation, indicating the functional differentiation within the thymus. 11 Such naturally occurring IL-17-producing ␥␦ T cells were already detected at the fetal stage as early as on embryonic day 15 (E15), when ␥␦ T cells began to develop. 11 Therefore, in ␥␦ T cells, the development and functional differentiation to IL-17 producers coincidentally occur within the fetal thymus. Intrathymic functional differentiation has been well documented for NKT cells. 12 During intrathymic development, NKT cell precursors acquire either an IL-4-or an IFN-␥-producing function at different stages. 13 Furthermore, there is a population of NKT cells that differentiates into IL-17-producing cells in the thymus independently of 14 Nevertheless, like Th17 cells, IL-17-producing NKT cells require ROR␥t for their development. 15 At present, the molecular mechanisms for the development of IL-17-producing ␥␦ T cells have not been defined, although it has been shown that IL-17-producing ␥␦ T cells developed normally in IL-6-deficient mice but were decreased in the absence of TGF-␤1. 16,17 In the present study, we found that Hes1, one of the basic helix-loop-helix (bHLH) proteins induced by Notch signaling, was specifically expressed in IL-17-producing ␥␦ T cells. Furthermore, Hes1, rather than STAT3 and ROR␥t, was critically involved in intrathymic development of IL-17-producing ␥␦ T cells. Expression of Hes1 is also important for IL-17 production by ␥␦ T cells in the periphery. Therefore, although Notch signaling is well known for its role in thymocyte development, it also regulates innate functions of ␥␦ T c...

Chronic treatment with calcitonin in osteoporotic patients alleviates the pain associated with this condition by an unknown mechanism. In ovariectomized rats that develop osteoporosis and hyperalgesia, we examined whether a functional change in serotonergic systems in the spinal dorsal horn was involved, using whole-cell recordings from substantia gelatinosa neurons in spinal cord slices and [(3)H]8-hydroxy-2(di-n-propylamino)tetralin ([(3)H]8-OH-DPAT) binding. Hyperalgesia could be attributed to the elimination of presynaptic inhibition by 5-HT of glutamatergic primary C-afferent terminals and an associated decrease in the density of [(3)H]8-OH-DPAT binding sites whose receptors are neither 5-HT(1A)- nor 5-HT(7)-subtype. These changes in serotonergic systems were restored after chronic treatment with calcitonin. Reversal of 5-HT receptor changes by calcitonin treatment may provide an explanation for its analgesic actions in patients.

Antiviral immune responses play as a double edged sword in resolution of infection and pathogenesis of acute lung injury caused by infection with highly pathogenic influenza A viruses. Here we show that type I interferons (IFNs) are important in protection against acute influenza A virus infection not only via their antiviral activity but also via their anti-inflammatory activity. IFN α receptor (IFNAR) knock-out (KO) mice exhibited increased mortality and morbidity with higher viral load after infection with influenza virus A/FM/1/47 (H1N1, a mouse-adapted strain) compared with wild-type (WT) mice, though the viruses were finally eliminated in both groups. The levels of proinflammatory cytokines in the lungs were significantly higher, while the level of IL-10 in the lungs was significantly lower in IFNAR KO mice than in WT mice during the course of infection. Restoration of IL-10 during an ongoing virus infection significantly reduced the levels of proinflammatory cytokines and improved mortality of IFNAR KO mice. These results suggest that type I IFNs are responsible not only for direct resolution of viral load but also for suppression of immunopathology caused by influenza A virus through IL-10 production.