A role for NKT cells has been implicated in sepsis, but the mechanism by which NKT cells contribute to sepsis remains unclear. Here, we examined WT and NKT-cell-deficient mice of C57BL/6 background during cecal ligation and puncture-induced sepsis. The levels of C5a, IFN-γ, and IL-10 were higher in the serum and peritoneal fluid of WT mice than in those of CD1d −/− mice, while the mortality rate was lower in CD1d −/− mice than in WT mice. C5a blockade decreased mortality of WT mice during sepsis, whereas it did not alter that of CD1d −/− mice. As assessed by intracellular staining, NKT cells expressed IFN-γ, while neutrophils expressed IL-10. Upon coculture, IL-10-deficient NKT cells enhanced IL-10 production by WT, but not IFN-γR-deficient, neutrophils. Meanwhile, CD1d −/− mice exhibited high CD55 expression on neutrophils during sepsis, whereas those cells from WT mice expressed minimal levels of CD55. Recombinant IL-10 administration into CD1d −/− mice reduced CD55 expression on neutrophils. Furthermore, adoptive transfer of sorted WT, but not IFN-γ-deficient, NKT cells into CD1d −/− mice suppressed CD55 expression on neutrophils, but increased IL-10 and C5a levels. Taken together, IFN-γ-producing NKT cells enhance C5a generation via IL-10-mediated inhibition of CD55 expression on neutrophils, thereby exacerbating sepsis.Keywords: C5a r IFN-γ r Neutrophils r NKT cell r Sepsis Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionNKT cells are a distinct T-cell subset characterized by the expression of natural killer receptors and semi-invariant TCRs. These cells recognize glycolipids presented by CD1d, an MHC class I-like Correspondence: Dr. Doo Hyun Chung e-mail: doohyun@snu.ac.kr protein expressed by APCs [1]. During bacterial infection, TCRs on NKT cells directly recognize glycolipids derived from certain Gramnegative bacterial membranes [2,3] and can be activated by innate cytokines secreted by dendritic cells that have been activated by microorganisms [2,4]. Furthermore, LPS-mediated engagement of TLR4 directly activates NKT cells in terms of differential * These authors contributed equally to this work. Eur. J. Immunol. 2014Immunol. . 44: 2025Immunol. -2035 cytokine production, thereby regulating immune diseases [5]. These findings suggest that NKT cells, activated during immune responses against bacteria, regulate bacteria-mediated pathologic processes such as sepsis. Sepsis is a complex inflammatory dysregulation that causes multiple organ dysfunction and coagulopathy, often resulting in death [6,7]. Several studies have demonstrated that NKT cells promote LPS-or cecal ligation and puncture (CLP)-induced sepsis in mice through the production of . Consistent with these findings, two independent studies have demonstrated that treatment of C57BL/6 mice with anti-CD1d antibody enhances survival rates during CLP-induced sepsis [11,12], suggesting that NKT-cell-mediated promotion of sepsis depends on an interaction between CD1d and TCR...

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Invariant natural killer T cells are a distinct subset of T cells that exert Janus-like functions. Moreover, Notch signaling is known to have critical roles in the development and functions of T cells. However, it is not known whether Notch signaling contributes to the development or functions of invariant natural killer T cells. Here, we found that CD4-specific gene ablation of Notch 1 and Notch 2 (N1N2(-/-)) increased the number of invariant natural killer T cells in the thymus but decreased them in the liver. N1N2(-/-) mice showed impaired thymic maturation of invariant natural killer T cells from the NK1.1(-)CD44(+) to the NK1.1(+)CD44(+) stage, resulting in accumulation of NK1.1(-)CD44(+) invariant natural killer T cells in the thymus. Upon activation, hepatic invariant natural killer T cells from N1N2(-/-) mice produced lower cytokine levels and increased apoptosis versus wild-type invariant natural killer T cells. Furthermore, Notch 1/Notch 2-deficient, but not wild type, invariant natural killer T cells failed to promote antibody-induced arthritis in CD1d(-/-) mice. Unlike N1N2(-/-) mice, RBP-j(lox) (/) (lox) CD4-Cre mice showed similar percentages and numbers of thymic invariant natural killer T cells to wild-type mice but had defects in their homeostasis, maturation, and cytokine production in the liver. Taken together, our data indicate distinct effects of Notch signaling on invariant natural killer T cells in the thymus and liver, which are at least partly independent of RBP-j in the thymus.

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NKT cell is a distinct T cell subset that links innate and adaptive immune responses. IL-1β, produced by various immune cells, plays critical role in the regulation of innate immunity in vivo. However, it is unclear whether NKT cells regulate IL-1β production in vivo. Here, we demonstrate that NKT cells regulate production of IL-1β by macrophages via producing GM-CSF and IL-4. Among cytokines secreted from NKT cells, GM-CSF enhanced IL-1β production by macrophages through regulating pro-IL-1β expression and NLRP3-dependent inflammasome activation, whereas IL-4 enhanced M2-differentiation of macrophages, thereby decreasing IL-1β production. Furthermore, NKT cells aggravated IL-1β-mediated peritonitis by producing GM-CSF, but attenuated peritonitis via producing IL-4. Taken together, our findings suggest the NKT cells exert double-sided effects on IL-1β-mediated innate immune responses by producing IL-4 and IL-1β.

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