The type 2 cytokines interleukin (IL)-4, IL-5, IL-9 and IL-13 play critical roles in stimulating innate and adaptive immune responses required for resistance to helminth infection and promotion of allergic inflammation, metabolic homeostasis and tissue repair1–3. Group 2 innate lymphoid cells (ILC2s) are a potent source of type 2 cytokines and while significant advances have been made in understanding the cytokine milieu that promotes ILC2 responses4–9, there are fundamental gaps in knowledge regarding how ILC2 responses are regulated by other stimuli. In this report, we demonstrate that ILC2s in the gastrointestinal tract co-localize with cholinergic neurons that express the neuropeptide neuromedin U (NMU)10,11. In contrast to other hematopoietic cells, ILC2s selectively express the NMU receptor 1 (NMUR1). In vitro stimulation of ILC2s with NMU induced rapid cell activation, proliferation and secretion of type 2 cytokines IL-5, IL-9 and IL-13 that was dependent on cell-intrinsic expression of NMUR1 and Gαq protein. In vivo administration of NMU triggered potent type 2 cytokine responses characterized by ILC2 activation, proliferation and eosinophil recruitment that was associated with accelerated expulsion of the gastrointestinal nematode Nippostrongylus brasiliensis or induction of lung inflammation. Conversely, worm burden was higher in Nmur1−/− mice compared to control mice. Further, use of gene-deficient mice and adoptive cell transfer experiments revealed that ILC2s were necessary and sufficient to mount NMU-elicited type 2 cytokine responses. Together, these data indicate that the NMU-NMUR1 neuronal signaling circuit provides a selective and previously unrecognized mechanism through which the enteric nervous system and innate immune system integrate to promote rapid type 2 cytokine responses that can induce anti-microbial, inflammatory and tissue-protective type 2 responses at mucosal sites.

Innate lymphoid cells (ILCs) including lymphoid tissue-inducer (LTi) cells, IL-22-producing NKp46 + innate cells and IL-13-producing nuocytes play important roles in regulating intestinal microbiota, defence against pathogens and formation of lymphoid tissue [1][2][3][4] . Their development is dependent on Id2 and Rorγt or Rorα 5-7 . Lineage tracing experiments have shown that the common lymphoid precursor gives rise to nuocytes, LTi cells and NKp46 + ILCs 6,8,9 , but these studies have not deciphered the discrete steps and transcription factors that specify ILC subset development, activation and maintenance. Whether NKp46 + ILCs arise directly from LTi cells, or rather represent a separate lineage that diverges earlier in development, remains controversial [10][11][12] . We investigated the requirement for the transcriptional master regulator T-bet (encoded by Tbx21) which is critical for the development of both T cells and NK cells 13,14 , in driving differentiation of ILC populations. Here we report that T-bet played an essential role for the development of NKp46 + ILCs, but was dispensable for LTi cells or nuocytes. Tbx21 +/+ LTi cells adopted an NKp46 + phenotype in vitro and in vivo but not in the absence of Tbx21. Decrease of T-bet expression coordinately reduced Notch1 and Notch2 and we show Notch signaling is necessary for the transition of LTi cells into NKp46 + ILCs. In addition, Tbx21 −/− mice have an accumulation in CD4 − LTi cells and differentiation into NKp46 + ILCs came solely from this population. Our results pinpoint T-bet as the critical regulator of NKp46 + ILC differentiation by regulation of Notch2 signaling. NKp46 + cells are an important element of the protective intestinal mucosal cellular arsenal, and here, we uncover the distinct molecular pathways that guide the development of NKp46 + ILCs. Supplementary Information is linked to the online version of the paper at www.nature.com/nature. Author InformationThe authors declare no competing financial interests. Europe PMC Funders GroupAuthor Manuscript Nat Immunol. Author manuscript; available in PMC 2014 July 01. Supplementary Fig. 2).Analysis of T-bet expression in innate lymphocyte populations by intracellular staining and mRNA levels revealed high expression of T-bet in both NKp46 + ILCs and NK (lin − Rorγt − NKp46 + NK1.1 + ) cells isolated from the intestine, while T-bet was not expressed in LTi cells (Fig. 1c). The related T-box factor Eomes, that performs similar functions to Tbet in CD8 + T cells and NK cells, was not expressed in NKp46 + ILCs or LTi cells ( Supplementary Fig. 3a). Thus, T-bet appears to play a crucial role in the development of NKp46 + ILCs. Similar to T-bet, Blimp1 (encoded by Prdm1) was strongly differentially expressed between LTi and NKp46 + ILC populations ( Supplementary Fig. 3b). However, mice homozygously deficient for Blimp1 (Blimp1 gfp/gfp ) did not show any apparent defect in the development of ILC subsets ( Supplementary Fig. 3c). Thus, Blimp1 is dispensable for ILC differentiation while T-b...

The type 2 inflammatory response is induced by various environmental and infectious stimuli. Although recent studies identified group 2 innate lymphoid cells (ILC2s) as potent sources of type 2 cytokines, the molecular pathways controlling ILC2 responses are incompletely defined. Here we demonstrate that murine ILC2s express the β-adrenergic receptor (βAR) and colocalize with adrenergic neurons in the intestine. βAR deficiency resulted in exaggerated ILC2 responses and type 2 inflammation in intestinal and lung tissues. Conversely, βAR agonist treatment was associated with impaired ILC2 responses and reduced inflammation in vivo. Mechanistically, we demonstrate that the βAR pathway is a cell-intrinsic negative regulator of ILC2 responses through inhibition of cell proliferation and effector function. Collectively, these data provide the first evidence of a neuronal-derived regulatory circuit that limits ILC2-dependent type 2 inflammation.

Intestinal T cells and group 3 innate lymphoid cells (ILC3) control the composition of the microbiota and gut immune responses. Within the gut there coexists ILC3 subsets which either express or lack the Natural cytoxicity receptor (NCR) NKp46. We identify here the transcriptional signature associated with the T-bet-dependent differentiation of NCR− ILC3 into NCR+ ILC3. Contrary to the prevailing view, we show by conditional deletion of the key ILC3 genes Stat3, Il22, Tbx21 and Mcl1 that NCR+ ILC3 were redundant for the control of mouse colonic infections with Citrobacter rodentium in the presence of T cells. However, NCR+ ILC3 were essential for cecum homeostasis. Our data show that interplay between intestinal ILC3 and adaptive lymphocytes results in robust complementary fail-safe mechanisms ensuring gut homeostasis.

Loss of Nfil3 selectively reduces Peyer’s patch formation, impairing recruitment and distribution of lymphocytes and compromising immune responses to inflammatory and infectious agents.

The cytokine IL-15 is required for natural killer (NK) cell homeostasis; however, the intrinsic mechanism governing this requirement remains unexplored. Here we identify the absolute requirement for myeloid cell leukaemia sequence-1 (Mcl1) in the sustained survival of NK cells in vivo. Mcl1 is highly expressed in NK cells and regulated by IL-15 in a dose-dependent manner via STAT5 phosphorylation and subsequent binding to the 3 0 -UTR of Mcl1. Specific deletion of Mcl1 in NK cells results in the absolute loss of NK cells from all tissues owing to a failure to antagonize pro-apoptotic proteins in the outer mitochondrial membrane. This NK lymphopenia results in mice succumbing to multiorgan melanoma metastases, being permissive to allogeneic transplantation and being resistant to toxic shock following polymicrobial sepsis challenge. These results clearly demonstrate a non-redundant pathway linking IL-15 to Mcl1 in the maintenance of NK cells and innate immune responses in vivo.

Innate lymphocyte populations play a central role in conferring protective immunity at the mucosal frontier. In this study, we demonstrate that T cell factor 1 (TCF-1; encoded by Tcf7), a transcription factor also important for NK and T cell differentiation, is expressed by multiple innate lymphoid cell (ILC) subsets, including GATA3+ nuocytes (ILC2) and NKp46+ ILCs (ILC3), which confer protection against lung and intestinal inflammation. TCF-1 was intrinsically required for the differentiation of both ILC2 and NKp46+ ILC3. Loss of TCF-1 expression impaired the capacity of these ILC subsets to produce IL-5, IL-13, and IL-22 and resulted in crippled responses to intestinal infection with Citrobacter rodentium. Furthermore, a reduction in T-bet expression required for Notch-2–dependent development of NKp46+ ILC3 showed a dose-dependent reduction in TCF-1 expression. Collectively, our findings demonstrate an essential requirement for TCF-1 in ILC2 differentiation and reveal a link among Tcf7, Notch, and Tbx21 in NKp46+ ILC3 development.

The essential roles played by the immune system in the discrimination between self- versus non/altered-self and its integral role in promoting host defense against invading microbes and tumors have been extensively studied for many years. In these contexts, significant advances have been made in defining the molecular and cellular networks that orchestrate cell-cell communication to mediate host defense and pathogen expulsion. Notably, recent studies indicate that in addition to these classical immune functions, cells of the innate and adaptive immune system also sense complex tissue- and environment-derived signals, including those from the nervous system and the diet. In turn these responses regulate physiologic processes in multiple tissues throughout the body, including nervous system function, metabolic state, thermogenesis, and tissue repair. In this review we propose an integrated view of how the mammalian immune system senses and interacts with other complex organ systems to maintain tissue and whole-body homeostasis.