Loss of Elp3 blocks intestinal tuft cell differentiation via an mTORC1-Atf4 axis.

Intestinal tuft cells are critical for anti-helminth parasite immunity because they produce IL-25, which triggers IL-13 secretion by activated group 2 innate lymphoid cells (ILC2s) to expand both goblet and tuft cells. We show that epithelial Elp3, a tRNA-modifying enzyme, promotes tuft cell differentiation and is consequently critical for IL-25 production, ILC2 activation, goblet cell expansion and control of Nippostrongylus brasiliensis helminth infection in mice. Elp3 is essential for the generation of intestinal immature tuft cells and for the IL-13-dependent induction of glycolytic enzymes such as Hexokinase 1 and Aldolase A. Importantly, loss of epithelial Elp3 in the intestine blocks the codon-dependent translation of the Gator1 subunit Nprl2, an mTORC1 inhibitor, which consequently enhances mTORC1 activation and stabilizes Atf4 in progenitor cells. Likewise, Atf4 overexpression in mouse intestinal epithelium blocks tuft cell differentiation in response to intestinal helminth infection. Collectively, our data define Atf4 as a negative regulator of tuft cells and provide insights into promotion of intestinal type 2 immune response to parasites through tRNA modifications.

Retraction: Rolot, M.; O'Sullivan, T.E. Living with Yourself: Innate Lymphoid Cell Immunometabolism. Cells 2020, 9, 334.

The journal retracts the article, "Rolot, M. and O'Sullivan, T. E. Living with Yourself: Innate lymphoid Cell Immunometabolism. Cells 2020, 9, 334" [...].

CRISPR-Cas9 Ribonucleoprotein-Mediated Genomic Editing in Mature Primary Innate Immune Cells.

CRISPR genome engineering has become a powerful tool to functionally investigate the complex mechanisms of immune system regulation. While decades of work have aimed to genetically reprogram innate immunity, the utility of current approaches is restricted by poor knockout efficiencies or limited specificity for mature cell lineages in vivo. Here, we describe an optimized strategy for non-viral CRISPR-Cas9 ribonucleoprotein (cRNP) genomic editing of mature primary mouse innate lymphocyte cells (ILCs) and myeloid lineage cells that results in an almost complete loss of single or double target gene expression from a single electroporation. Furthermore, we describe in vivo adoptive transfer mouse models that can be utilized to screen for gene function during viral infection using cRNP-edited naive natural killer (NK) cells and bone-marrow-derived conventional dendritic cell precursors (cDCPs). This resource will enhance target gene discovery and offer a specific and simplified approach to gene editing in the mouse innate immune system.

Living with Yourself: Innate Lymphoid Cell Immunometabolism.

Innate lymphoid cells (ILCs) are tissue-resident sentinels of the immune system that function to protect local tissue microenvironments against pathogens and maintain homeostasis. However, because ILCs are sensitively tuned to perturbations within tissues, they can also contribute to host pathology when critical activating signals become dysregulated. Recent work has demonstrated that the crosstalk between ILCs and their environment has a significant impact on host metabolism in health and disease. In this review, we summarize studies that support evidence for the ability of ILCs to influence tissue and systemic metabolism, as well as how ILCs can be regulated by environmental changes in systemic host metabolism. We also highlight studies demonstrating how ILC- intrinsic metabolism influences their activation, proliferation, and homeostasis. Finally, this review discusses the challenges and open questions in the rapidly expanding field of ILCs and immunometabolism.

Pre-conception maternal helminth infection transfers via nursing long-lasting cellular immunity against helminths to offspring.

Maternal immune transfer is the most significant source of protection from early-life infection, but whether maternal transfer of immunity by nursing permanently alters offspring immunity is poorly understood. Here, we identify maternal immune imprinting of offspring nursed by mothers who had a pre-conception helminth infection. Nursing of pups by helminth-exposed mothers transferred protective cellular immunity to these offspring against helminth infection. Enhanced control of infection was not dependent on maternal antibody. Protection associated with systemic development of protective type 2 immunity in T helper 2 (TH2) impaired IL-4Rα-/- offspring. This maternally acquired immunity was maintained into maturity and required transfer (via nursing) to the offspring of maternally derived TH2-competent CD4 T cells. Our data therefore reveal that maternal exposure to a globally prevalent source of infection before pregnancy provides long-term nursing-acquired immune benefits to offspring mediated by maternally derived pathogen-experienced lymphocytes.

Recruitment of hepatic macrophages from monocytes is independent of IL-4Rα but is associated with ablation of resident macrophages in schistosomiasis.

Alternatively activated Mφs (AAMφ) accumulate in hepatic granulomas during schistosomiasis and have been suggested to originate in the bone marrow. What is less understood is how these Mφ responses are regulated after S. mansoni infection. Here, we investigated the role of IL-4 receptor α-chain (IL-4Rα)-signalling in the dynamics of liver Mφ responses. We observed that IL-4Rα signalling was dispensable for the recruitment of Ly6Chi monocytes and for their conversion into F4/80hi CD64hi CD11bhi Mφ. Moreover, while IL-4Rα provided an AAMφ phenotype to liver F4/80hi CD64hi CD11bhi Mφ that was associated with regulation of granuloma formation, it was dispensable for host survival. Resident F4/80hi CD64hi CD11blo Mφ did not upregulate the AAMφ signature gene Ym1. Rather, resident Mφ nearly disappeared by week 8 after infection and artificial ablation of resident Mφ in CD169DTR mice did not affect the response to S. mansoni infection. Interestingly, ablation of CD169+ cells in naive mice resulted in the accumulation of F4/80hi CD64hi CD11bhi Mφ, which was amplified when ablation occurred during schistosomiasis. Altogether, our results suggest the ablation of resident KCs after S. mansoni infection to be associated with the recruitment and accumulation of F4/80hi CD64hi CD11bhi Mφ with lyz2-dependent IL-4Rα contributing to the regulation of granuloma inflammation but being dispensable for host survival.

Helminth-induced IL-4 expands bystander memory CD8+ T cells for early control of viral infection.

Infection with parasitic helminths can imprint the immune system to modulate bystander inflammatory processes. Bystander or virtual memory CD8+ T cells (TVM) are non-conventional T cells displaying memory properties that can be generated through responsiveness to interleukin (IL)-4. However, it is not clear if helminth-induced type 2 immunity functionally affects the TVM compartment. Here, we show that helminths expand CD44hiCD62LhiCXCR3hiCD49dlo TVM cells through direct IL-4 signaling in CD8+ T cells. Importantly, helminth-mediated conditioning of TVM cells provided enhanced control of acute respiratory infection with the murid gammaherpesvirus 4 (MuHV-4). This enhanced control of MuHV-4 infection could further be explained by an increase in antigen-specific CD8+ T cell effector responses in the lung and was directly dependent on IL-4 signaling. These results demonstrate that IL-4 during helminth infection can non-specifically condition CD8+ T cells, leading to a subsequently raised antigen-specific CD8+ T cell activation that enhances control of viral infection.

Macrophage Activation and Functions during Helminth Infection: Recent Advances from the Laboratory Mouse.

Macrophages are highly plastic innate immune cells that adopt an important diversity of phenotypes in response to environmental cues. Helminth infections induce strong type 2 cell-mediated immune responses, characterized among other things by production of high levels of interleukin- (IL-) 4 and IL-13. Alternative activation of macrophages by IL-4 in vitro was described as an opposite phenotype of classically activated macrophages, but the in vivo reality is much more complex. Their exact activation state as well as the role of these cells and associated molecules in type 2 immune responses remains to be fully understood. We can take advantage of a variety of helminth models available, each of which have their own feature including life cycle, site of infection, or pathological mechanisms influencing macrophage biology. Here, we reviewed the recent advances from the laboratory mouse about macrophage origin, polarization, activation, and effector functions during parasitic helminth infection.