The transcription factor HIF-1α mediates plasticity of NKp46+ innate lymphoid cells in the gut

Gut innate lymphoid cells (ILCs) show remarkable phenotypic diversity, yet microenvironmental factors that drive this plasticity are incompletely understood. The balance between NKp46+, IL-22–producing, group 3 ILCs (ILC3s) and interferon (IFN)-γ–producing group 1 ILCs (ILC1s) contributes to gut homeostasis. The gut mucosa is characterized by physiological hypoxia, and adaptation to low oxygen is mediated by hypoxia-inducible transcription factors (HIFs). However, the impact of HIFs on ILC phenotype and gut homeostasis is not well understood. Mice lacking the HIF-1α isoform in NKp46+ ILCs show a decrease in IFN-γ–expressing, T-bet+, NKp46+ ILC1s and a concomitant increase in IL-22–expressing, RORγt+, NKp46+ ILC3s in the gut mucosa. Single-cell RNA sequencing revealed HIF-1α as a driver of ILC phenotypes, where HIF-1α promotes the ILC1 phenotype by direct up-regulation of T-bet. Loss of HIF-1α in NKp46+ cells prevents ILC3-to-ILC1 conversion, increases the expression of IL-22–inducible genes, and confers protection against intestinal damage. Taken together, our results suggest that HIF-1α shapes the ILC phenotype in the gut.

Porcine intestinal innate lymphoid cells and lymphocyte spatial context revealed through single-cell RNA sequencing

Intestinal lymphocytes are crucial members of the mucosal immune system with impact over outcomes of intestinal health versus dysbiosis. Resolving intestinal lymphocyte complexity and function is a challenge, as the intestine provides cellular snapshots of a diverse spectrum of immune states. In pigs, intestinal lymphocytes are poorly described relative to humans or traditional model species. Enhanced understanding of porcine intestinal lymphocytes will promote food security and improve utility of pigs as a biomedical model for intestinal research. Single-cell RNA sequencing (scRNA-seq) was performed to provide transcriptomic profiles of lymphocytes in the porcine ileum, with 31,983 cells annotated into 26 cell types. Deeper interrogation revealed previously undescribed cells in porcine ileum, including SELLhi γδ T cells, group 1 and group 3 innate lymphoid cells (ILCs), and four subsets of B cells. Single-cell transcriptomes in ileum were compared to those in porcine blood, and subsets of activated lymphocytes were detected in ileum but not periphery. Comparison to scRNA-seq human and murine ileum data revealed a general consensus of ileal lymphocytes across species. Lymphocyte spatial context in porcine ileum was conferred through differential tissue dissection prior to scRNA-seq. Antibody-secreting cells, B cells, follicular αβ T cells, and cycling T/ILCs were enriched in ileum with Peyer's patches, while non-cycling γδ T, CD8 αβ T, and group 1 ILCs were enriched in ileum without Peyer's patches. scRNA-seq findings were leverages to develop advanced toolsets for further identification of ILCs in porcine ileum via flow cytometry and in situ staining. Porcine ileal ILCs identified via scRNA-seq did not transcriptionally mirror peripheral ILCs (corresponding to natural killer cells) but instead had gene signatures indicative of tissue- and activation-specific functions, indicating potentially similar roles to intestinal ILCs identified in humans. Overall, the data serve as a highly-resolved transcriptomic atlas of the porcine intestinal immune landscape and will be useful in further understanding intestinal immune cell function.

Increased blood group 2 innate lymphoid cells are involved in blood eosinophilia and itching in Kimura disease

Background: Kimura disease (KD) is a rare, chronic inflammatory disorder characterized by blood eosinophilia, general itching, and subcutaneous head and neck mass lesions; however, the etiology of this disease is unknown. We hypothesized that group 2 innate lymphoid cells (ILC2s) in peripheral blood may play an essential role in the pathogenesis of KD. Methods: The prevalence of blood ILC2s and their ability to produce interleukin (IL) -4, IL-5, IL-13, and IL-31 in patients with KD were compared with those in control subjects and in patients with house dust mite (HDM) -induced allergic rhinitis (AR). Changes in blood ILC2 prevalence, blood eosinophilia, and clinical symptoms after surgery and steroid therapy were evaluated. Results: Blood ILC2 prevalence in patients with KD were eight times and six times higher than those in control subjects and in patients with AR, respectively. There was a strong positive correlation between ILC2 prevalence and blood eosinophilia. Patients with KD showed increased serum IL-13 and decreased IL-31 levels. KD patient-derived blood ILC2s produced large amounts of IL-5 and IL-13 in response to prostaglandin (PG) D and leukotriene (LT) D , compared to ILC2s derived from control subjects and patients with AR. Surgery and systemic steroid therapy ameliorated general itching with a concomitant decrease in blood ILC2s and blood eosinophilia. Upon disease recurrence, blood ILC2 prevalence and blood eosinophilia increased concurrently with general itching. Conclusion: Increased blood ILC2s may be involved in blood eosinophilia and general itching through the production of IL-5 and IL-13 in patients with KD.

Innate Lymphoid Cells in Autoimmune Diseases

Innate lymphoid cells (ILC) are a heterogeneous group of immune cells characterized by lymphoid morphology and cytokine profile similar to T cells but which do not express clonally distributed diverse antigen receptors. These particular cells express transcription factors and cytokines reflecting their similarities to T helper (Th)1, Th2, and Th17 cells and are therefore referred to as ILC1, ILC2, and ILC3. Other members of the ILC subsets include lymphoid tissue inducer (LTi) and regulatory ILC (ILCreg). Natural killer (NK) cells share a common progenitor with ILC and also exhibit a lymphoid phenotype without antigen specificity. ILC are found in low numbers in peripheral blood but are much more abundant at barrier sites such as the skin, liver, airways, lymph nodes, and the gastrointestinal tract. They play an important role in innate immunity due to their capacity to respond rapidly to pathogens through the production of cytokines. Recent evidence has shown that ILC also play a key role in autoimmunity, as alterations in their number or function have been identified in systemic lupus erythematosus, systemic sclerosis, and rheumatoid arthritis. Here, we review recent advances in the understanding of the role of ILC in the pathogenesis of autoimmune diseases, with particular emphasis on their role as a potential diagnostic biomarker and as therapeutic targets.

Circulating Innate Lymphoid Cells Exhibit Distinctive Distribution During Normal Pregnancy

Over the past decades, the investigation of innate lymphoid cells (ILCs) has revealed their significance in successful pregnancy. Sex hormones, such as estradiol and progesterone, show specific changes during pregnancy and modulate both adaptive and innate immune systems. ILC subset distribution in peripheral blood of pregnant women and its potential association with sex hormone levels have not been well revealed. Peripheral blood was obtained from healthy non-pregnant, early-pregnant, and late-pregnant women. Radioimmunoassay was performed to measure plasma estradiol and progesterone levels. The levels of type 1 ILCs (ILC1s), type 2 ILCs (ILC2s), type 3 ILCs (ILC3s), and total ILCs as well as estrogen and progesterone receptors of ILC2s in peripheral blood were analyzed using flow cytometry. The proportion of total ILCs and distribution of ILC subsets in peripheral blood changed dynamically during pregnancy. Compared to non-pregnant women, late-pregnant women displayed significantly higher proportion of circulating ILCs, among which ILC2s accounted for the majority in late-pregnant women while a smaller part in others, and ILC3s displayed the opposite. Plasma estradiol and progesterone levels elevated while pregnancy proceeded and the expression of their receptors in ILC2s increased consisted with the proportion of circulating ILC2s. Our work first observed the existence of progesterone receptors in human circulating ILC2s and revealed the distribution pattern of circulating ILC subsets and their interrelation with plasma sex hormone levels during pregnancy. Our results suggested that the estradiol and progesterone levels might partly influence the distribution of circulating ILC subsets and implied the interplay between circulating ILCs and pregnancy.