Migration and homing of immune cells are critical for immune surveillance. Trafficking is mediated by combinations of adhesion and chemokine receptors that guide immune cells, in response to chemokine signals, to specific locations within tissues and the lymphatic system to support tissue-localized immune reactions and systemic immunity1,2. Here we show that disruption of leukaemia inhibitory factor (LIF) production from group 2 innate lymphoid cells (ILC2s) prevents immune cells leaving the lungs to migrate to the lymph nodes (LNs). In the absence of LIF, viral infection leads to plasmacytoid dendritic cells (pDCs) becoming retained in the lungs where they improve tissue-localized, antiviral immunity, whereas chronic pulmonary allergen challenge leads to marked immune cell accumulation and the formation of tertiary lymphoid structures in the lung. In both cases immune cells fail to migrate to the lymphatics, leading to highly compromised LN reactions. Mechanistically, ILC2-derived LIF induces the production of the chemokine CCL21 from lymphatic endothelial cells lining the pulmonary lymphatic vessels, thus licensing the homing of CCR7+ immune cells (including dendritic cells) to LNs. Consequently, ILC2-derived LIF dictates the egress of immune cells from the lungs to regulate tissue-localized versus systemic immunity and the balance between allergen and viral responsiveness in the lungs.

Innate lymphoid cells (ILCs) are critical in maintaining tissue homeostasis, and during infection and inflammation. Here we identify, by using combinatorial reporter mice, a rare ILC progenitor (ILCP) population, resident to the small intestinal lamina propria (siLP) in adult mice. Transfer of siLP-ILCP into recipients generates group 1 ILCs (including ILC1 and NK cells), ILC2s and ILC3s within the intestinal microenvironment, but almost exclusively group 1 ILCs in the liver, lung and spleen. Single cell gene expression analysis and high dimensional spectral cytometry analysis of the siLP-ILCPs and ILC progeny indicate that the phenotype of the group 1 ILC progeny is also influenced by the tissue microenvironment. Thus, a local pool of siLP-ILCP can contribute to pan-ILC generation in the intestinal microenvironment but has more restricted potential in other tissues, with a greater propensity than bone marrow-derived ILCPs to favour ILC1 and ILC3 production. Therefore, ILCP potential is influenced by both tissue of origin and the microenvironment during development. This may provide additional flexibility during the tuning of immune reactions. The small intestinal lamina propria is rich in innate lymphoid cells, which are important contributors of mucosal immunity. Here authors identify a small progenitor cell population that can develop into all types of innate lymphoid cells in their intestinal microenvironment but their developmental potential becomes more restricted when placed into other tissues, such as liver, lung or spleen.

The development of innate lymphoid cell (ILC) transcription factor reporter mice has shown a previously unexpected complexity in ILC hematopoiesis. Using novel polychromic mice to achieve higher phenotypic resolution, we have characterized bone marrow progenitors that are committed to the group 1 ILC lineage. These common ILC1/NK cell progenitors (ILC1/NKP), which we call "aceNKPs", are defined as lineage – Id2 + IL-7Rα + CD25 – α4β7 – NKG2A/C/E + Bcl11b – . In vitro, aceNKPs differentiate into group 1 ILCs, including NK-like cells that express Eomes without the requirement for IL-15, and produce IFN-γ and perforin upon IL-15 stimulation. Following reconstitution of Rag2 –/– Il2rg –/– hosts, aceNKPs give rise to a spectrum of mature ILC1/NK cells (regardless of their tissue location) that cannot be clearly segregated into the traditional ILC1 and NK subsets, suggesting that group 1 ILCs constitute a dynamic continuum of ILCs that can develop from a common progenitor. In addition, aceNKP-derived ILC1/NK cells effectively ameliorate tumor burden in a model of lung metastasis, where they acquired a cytotoxic NK cell phenotype. Our results identify the primary ILC1/NK progenitor that lacks ILC2 or ILC3 potential and is strictly committed to ILC1/NK cell production irrespective of tissue homing.

Background Colorectal cancer (CRC) is the second leading cause of cancer-related death. The majority of CRC cases are caused by mutations in the adenomatous polyposis coli gene (APC), and are resistant to current cancer immunotherapies. Most immunotherapeutic strategies rely on utilising adaptive T cells, and their lack of efficacy in CRC suggests there may be immunosuppressive signals in the tumour microenvironment. Using a mouse model of APC-mutation-driven CRC, recent work by our lab has shown that interleukin 25 (IL-25)-activated group 2 innate lymphoid cells (ILC2s) promote intestinal tumourigenesis through activation of monocytic myeloid-derived suppressor cells (M-MDSCs) and the resulting suppression of CD8+ T cells.1 However, the impact of IL-25 and ILC2s on individual intestinal tumour morphology is not completely understood. In this study, we use histological techniques to investigate the impact of genetic ablation of IL-25 or ILC2s on the morphology of APC-mutation-driven mouse intestinal tumours. Materials and Methods The mouse strains used were Apc1322T, Il25tom, Il7raCre and Roraflox on a C57BL/6Ola genetic background.1Apc1322T/+Il25tom/tom and Apc1322T/+Roraflox/flox Il7raCre/+ mice were used to investigate the effect of IL-25 deficiency or ILC2 deficiency, respectively, on intestinal tumours. Small intestinal tissue was fixed in 4% formaldehyde for 24 h and dehydrated. Intestines were embedded in paraffin and sectioned at 4 μm for histology, or 7.5% gelatin + 10% sucrose in PBS, followed by cryosectioning at 20 μm for immunohistochemistry. Paraffin sections were stained with hematoxylin and eosin (H&E) or Ki67 according to standard methods. For immunohistochemistry, cryosections were stained overnight at 4°C with fluorescent antibodies. Results H&E images confirmed that transgenic Apc1322Tmice lacking IL-25 had smaller tumours and showed less dysplasia than Apc1322T mice with normal IL-25 expression. Ki67 staining showed that tumours express higher Ki67 levels than adjacent normal intestinal tissue. The tumour-associated tertiary lymphoid structures (TATLS) of Apc1322T mice lacking IL-25 appeared larger, indicating a more robust anti-tumour immune response. Likewise, Apc1322Tmice lacking ILC2s had smaller, less dysplastic tumours. TATLS in these mice were bigger than mice with ILC2s but smaller than Apc1322T mice lacking IL-25, indicating that IL-25 may act via additional protumourigenic cell types. Immunohistochemistry confirmed the presence of ILC2s, as well as MDSCs the tumours of Apc1322Tmice, suggesting that these cells create an immunosuppressive niche. Conclusions This pilot study confirms that genetic ablation of either IL-25 or ILC2s promotes anti-tumour immune reactions and decreases tumour size, correlating with reduced intestinal tumour proliferative capacity and dysplasia. Mice lacking IL-25 or ILC2s had larger TATLS, which are known to be associated with improved prognosis in patients. This study, along with previous data, highlights the potential therapeutic benefit of targeting the IL-25-ILC2 axis for colorectal cancer. Further studies are required to bring this from bench to bedside. Reference Jou E, et al. An innate IL-25-ILC2-MDSC axis creates a cancer-permissive microenvironment for Apc mutation-driven intestinal tumorigenesis. Sci Immunol 2022 Jun 3;7(72):eabn0175. Disclosure Information E. Jou: None. R.J. Hill: None. J.E. Murphy: None. N. Rodriguez-Rodriguez: None. M. Ko: None. A.N.J. McKenzie: None.

Methyl farnesoate (MF) is the crustacean homolog of the insect juvenile hormone and is believed to regulate growth and reproduction in crustaceans. Farnesoic acid O-methyltransferase (FAMeT) catalyzes the conversion of farnesoic acid (FA) to MF. Here we report the cloning and characterization of two forms of FAMeTs (i.e. LvFAMeT-S and LvFAMeT-L) from the shrimp Litopenaeus vannamei. LvFAMeT transcript has a wide tissue distribution pattern in L. vannamei and is also expressed in nauplius, zoea, mysis, post-larval stages and adults. Unlike FAMeTs reported in other decapods, transcripts of two different sizes were detected in L. vannamei. We postulate that the wide distribution of LvFAMeT expression may be related to its role in growth and regulation of molting. To study the functions of LvFAMeT in molting, the RNA interference (RNAi) technique was used. Injection of double stranded RNA (dsRNA) for LvFAMeT knocked down the expression of LvFAMeT in shrimp for at least 3 days and the shrimp did not advance to the final stage of molt cycle. Furthermore, the expression of the molt-related genes encoding cathepsin-L and the hemocyanin gene was disturbed. Subsequently, 100% mortality of the shrimp was observed in the LvFAMeT dsRNA-injected shrimp. In contrast, control shrimp completed their molt and proceeded to the next molt cycle. We postulate that, as an important enzyme for the conversion of FA to MF, RNAi injection knocked down the expression of LvFAMeT which could potentially result in a decrease in the production of MF and subsequently, could affect the molting process. The newly identified LvFAMeT may be involved in the control of molting in shrimp. The results of this study demonstrate the potential use of the RNA interference technique to study other putative genes identified in crustaceans.

Atherosclerotic cardiovascular disease causes heart attacks and strokes, which are the leading causes of mortality worldwide1. The formation of atherosclerotic plaques is initiated when low-density lipoproteins bind to heparan-sulfate proteoglycans (HSPGs)2 and become trapped in the subendothelial space of large and medium size arteries, which leads to chronic inflammation and remodelling of the artery wall2. A proliferation-inducing ligand (APRIL) is a cytokine that binds to HSPGs3, but the physiology of this interaction is largely unknown. Here we show that genetic ablation or antibody-mediated depletion of APRIL aggravates atherosclerosis in mice. Mechanistically, we demonstrate that APRIL confers atheroprotection by binding to heparan sulfate chains of heparan-sulfate proteoglycan 2 (HSPG2), which limits the retention of low-density lipoproteins, accumulation of macrophages and formation of necrotic cores. Indeed, antibody-mediated depletion of APRIL in mice expressing heparan sulfate-deficient HSPG2 had no effect on the development of atherosclerosis. Treatment with a specific anti-APRIL antibody that promotes the binding of APRIL to HSPGs reduced experimental atherosclerosis. Furthermore, the serum levels of a form of human APRIL protein that binds to HSPGs, which we termed non-canonical APRIL (nc-APRIL), are associated independently of traditional risk factors with long-term cardiovascular mortality in patients with atherosclerosis. Our data reveal properties of APRIL that have broad pathophysiological implications for vascular homeostasis.