Alistair L. Chenery

The recent revolution in tissue-resident macrophage biology has resulted largely from murine studies performed in the C57BL/6 strain. Here, we provide a comprehensive analysis of immune cells in the pleural cavity using both C57BL/6 and BALB/c mice. Unlike C57BL/6 mice, naïve tissue-resident Large Cavity Macrophages (LCM) of BALB/c mice failed to fully implement the tissue residency program. Following infection with a pleural-dwelling nematode these pre-existing differences were accentuated with LCM expansion occurring in C57BL/6 but not BALB/c mice. While infection drove monocyte recruitment in both strains, only in C57BL/6 mice were monocytes able to efficiently integrate into the resident pool. Monocyte to macrophage conversion required both T cells and IL-4Rα signalling. Host genetics are therefore a key influence on tissue resident macrophage biology, and during nematode infection Th2 cells control the differentiation pathway of tissue resident macrophages. Graphical

IL-13 is implicated in effective repair after acute lung injury and the pathogenesis of chronic diseases such as allergic asthma. Both these processes involve matrix remodelling, but understanding the specific contribution of IL-13 has been challenging because IL-13 shares receptors and signalling pathways with IL-4. Here, we used Nippostrongylus brasiliensis infection as a model of acute lung damage comparing responses between WT and IL-13-deficient mice, in which IL-4 signalling is intact. We found that IL-13 played a critical role in limiting tissue injury and haemorrhaging in the lung, and through proteomic and transcriptomic profiling, identified IL-13-dependent changes in matrix and associated regulators. We further showed a requirement for IL-13 in the induction of epithelial-derived type 2 effector molecules such as RELM-α and surfactant protein D. Pathway analyses predicted that IL-13 induced cellular stress responses and regulated lung epithelial cell differentiation by suppression of Foxa2 pathways. Thus, in the context of acute lung damage, IL-13 has tissue-protective functions and regulates epithelial cell responses during type 2 immunity.

Alternatively activated macrophages are essential effector cells during type 2 immunity and tissue repair following helminth infections. We previously showed that Ym1, an alternative activation marker, can drive innate IL-1R–dependent neutrophil recruitment during infection with the lung-migrating nematode, Nippostrongylus brasiliensis, suggesting a potential role for the inflammasome in the IL-1–mediated innate response to infection. Although inflammasome proteins such as NLRP3 have important proinflammatory functions in macrophages, their role during type 2 responses and repair are less defined. We therefore infected Nlrp3^−/− mice with N. brasiliensis. Unexpectedly, compared with wild-type (WT) mice, infected Nlrp3^−/− mice had increased neutrophilia and eosinophilia, correlating with enhanced worm killing but at the expense of increased tissue damage and delayed lung repair. Transcriptional profiling showed that infected Nlrp3^−/− mice exhibited elevated type 2 gene expression compared with WT mice. Notably, inflammasome activation was not evident early postinfection with N. brasiliensis, and in contrast to Nlrp3^−/− mice, antihelminth responses were unaffected in caspase-1/11–deficient or WT mice treated with the NLRP3-specific inhibitor MCC950. Together these data suggest that NLRP3 has a role in constraining lung neutrophilia, helminth killing, and type 2 immune responses in an inflammasome-independent manner. Key Points Nlrp3^−/− mice have enhanced early antihelminth immunity in the lung. Type 2 immunity and repair responses are dysregulated in Nlrp3^−/− mice. NLRP3 plays an inflammasome-independent role during Nippostrongylus infection.

Nippostrongylus brasiliensis is a well-defined model of type-2 immunity but the early lung-migrating phase is dominated by innate IL-17A production and neutrophilia. Using N. brasiliensis infection we confirm previous observations that Il17a -KO mice exhibit an impaired type-2 immune response. Neutrophil depletion and reconstitution studies demonstrated that neutrophils contribute to the subsequent eosinophilia but are not responsible for the ability of IL-17A to promote type-2 cytokine responses. Transcriptional profiling of the lung on day 2 of N. brasiliensis infection revealed an increased Ifnγ signature in the Il17a -KO mice confirmed by enhanced IFNγ protein production. Depletion of early IFNγ rescued type-2 immune responses in the Il17a -KO mice demonstrating that IL-17A-mediated suppression of IFNγ promotes type-2 immunity. Notably, when IL-17A was blocked later in infection, the type-2 response increased. IL-17A regulation of type-2 immunity was lung-specific and infection with Trichuris muris, revealed that IL-17A promotes a type-2 immune response in the lung even when a parasite lifecycle is restricted to the intestine. Together our data reveal IL-17A as a major regulator of pulmonary type-2 immunity which supports the development of a protective type-2 immune response but subsequently limits the magnitude of that response.

Background and Purpose—: A major process contributing to cell death in the ischemic brain is inflammation. Inflammasomes are multimolecular protein complexes that drive inflammation through activation of proinflammatory cytokines, such as IL (interleukin)-1β. Preclinical evidence suggests that IL-1β contributes to a worsening of ischemic brain injury. Methods—: Using a mouse middle cerebral artery thrombosis model, we examined the inflammatory response after stroke and the contribution of the NLRP3 (NACHT, LRR and PYD domains-containing protein 3) inflammasome to ischemic injury. Results—: There was a marked inflammatory response after stroke characterized by increased expression of proinflammatory cytokines and NLRP3 and by recruitment of leukocytes to the injured tissue. Targeting NLRP3 with the inhibitor MCC950, or using mice in which NLRP3 was knocked out, had no effect on the extent of injury caused by stroke. Conclusions—: These data suggest that the NLRP3 pathway does not contribute to the inflammation exacerbating ischemic brain damage, contradicting several recent reports to the contrary.

Alternatively activated macrophages are essential effector cells during type 2 immunity and tissue repair following helminth infections. We previously showed that Ym1, an alternative activation marker, can drive innate IL-1R-dependent neutrophil recruitment during infection with the lung-migrating nematode, Nippostrongylus brasiliensis suggesting a potential role for the inflammasome in the IL-1-mediated innate response to infection. While inflammasome proteins such as NLRP3 have important pro-inflammatory functions in macrophages, their role during type 2 responses and repair are less defined. We therefore infected Nlrp3 ^−/− mice with N. brasiliensis . Unexpectedly, compared to WT mice, infected Nlrp3 ^−/− mice had increased neutrophilia and eosinophilia, correlating with enhanced worm killing but at the expense of increased tissue damage and delayed lung repair. Transcriptional profiling showed that infected Nlrp3 ^−/− mice exhibited elevated type 2 gene expression compared to WT mice. Notably, inflammasome activation was not evident early post-infection with N. brasiliensis and in contrast to Nlrp3 ^−/− mice, anti-helminth responses were unaffected in caspase-1/11 deficient or WT mice treated with the NLRP3-specific inhibitor MCC950. Together these data suggest that NLRP3 can constrain lung neutrophilia and helminth killing and negatively regulate type 2 immune responses in an inflammasome-independent manner.

The intestinal immune system must be able to respond to a wide variety of infectious organisms while maintaining tolerance to non-pathogenic microbes and food antigens. The Vitamin A metabolite all-trans-retinoic acid (atRA) has been implicated in the regulation of this balance, partially by regulating innate lymphoid cell (ILC) responses in the intestine. However, the molecular mechanisms of atRA-dependent intestinal immunity and homeostasis remain elusive. Here we define a role for the transcriptional repressor Hypermethylated in cancer 1 (HIC1, ZBTB29) in the regulation of ILC responses in the intestine. Intestinal ILCs express HIC1 in a vitamin A-dependent manner. In the absence of HIC1, group 3 ILCs (ILC3s) that produce IL-22 are lost, resulting in increased susceptibility to infection with the bacterial pathogen Citrobacter rodentium. Thus, atRA-dependent expression of HIC1 in ILC3s regulates intestinal homeostasis and protective immunity. Innate lymphoid cells (ILCs) are emerging as important regulators of immune responses at barrier sites such as the intestine. However, the molecular mechanisms that control this are not well described. In the intestine, the Vitamin A metabolite all-trans-retinoic acid (atRA) has been shown to be an important component of the homeostatic mechanisms. In this manuscript, we show that the atRA-dependent transcription factor Hypermethylated in cancer 1 (HIC1, ZBTB29) is required for ILC homeostasis and function in the steady state as well as following infection with the bacterial pathogen Citrobacter rodentium. Thus, HIC1 links RA signalling to intestinal immune responses. Further, our results identify HIC1 as a potential target to modulate ILC responses in vivo in health and disease.

The incidence of inflammatory bowel diseases (IBDs) has steadily increased in recent decades—a phenomenon that cannot be explained by genetic mutations alone. Other factors, including the composition of the intestinal microbiome, are potentially important contributors to the increased occurrence of this group of diseases. Previous reports have shown a correlation between early-life antibiotic (Abx) treatment and an increased incidence of IBD. In this report, we investigated the effects of early-life Abx treatments on the pathogenicity of CD4⁺ T cells using an experimental T cell transfer model of IBD. Our results show that CD4⁺ T cells isolated from adult mice that had been treated with Abx during gestation and in early life induced a faster onset of IBD in Rag1-deficient mice compared with CD4⁺ T cells of untreated mice. Ex vivo functional analyses of IBD-inducing CD4⁺ T cells did not show significant differences in their immunologic potential ex vivo, despite their in vivo phenotype. However, genome-wide gene-expression analysis revealed that these cells displayed dysregulated expression of genes associated with cell-cycle regulation, metabolism, and cellular stress. Analysis of Abx-treated CD4⁺ T cell donors showed systemically elevated levels of the stress hormone corticosterone throughout life compared with untreated donors. The cohousing of Abx-treated mice with untreated mice decreased serum corticosterone, and a consequent transfer of the cells from cohoused mice into Rag1-deficient mice restored the onset and severity of disease to that of untreated animals. Thus, our results suggest that early-life Abx treatment results in a stress response with high levels of corticosterone that influences CD4⁺ T cell function.