Role of hepatocyte-derived IL-7 in maintenance of intrahepatic NKT cells and T cells and development of B cells in fetal liver

B Cells of Early-life Origin Defined by RAG2-based Lymphoid Cell Tracking under Native Hematopoietic Conditions

During the perinatal period, the immune system sets the threshold to select either response or tolerance to environmental Ags, which leads to the potential to provide a lifetime of protection and health. B-1a B cells have been demonstrated to develop during this perinatal time window, showing a unique and restricted BCR repertoire, and these cells play a major role in natural Ab secretion and immune regulation. In the current study, we developed a highly efficient temporally controllable RAG2-based lymphoid lineage cell labeling and tracking system and applied this system to understand the biological properties and contribution of B-1a cells generated at distinct developmental periods to the adult B-1a compartments. This approach revealed that B-1a cells with a history of RAG2 expression during the embryonic and neonatal periods dominate the adult B-1a compartment, including those in the bone marrow (BM), peritoneal cavity, and spleen. Moreover, the BCR repertoire of B-1a cells with a history of RAG2 expression during the embryonic period was restricted, becoming gradually more diverse during the neonatal period, and then heterogeneous at the adult stage. Furthermore, more than half of plasmablasts/plasma cells in the adult BM had embryonic and neonatal RAG2 expression histories. Moreover, BCR analysis revealed a high relatedness between BM plasmablasts/plasma cells and B-1a cells derived from embryonic and neonatal periods, suggesting that these cell types have a common origin. Taken together, these findings define, under native hematopoietic conditions, the importance in adulthood of B-1a cells generated during the perinatal period.

Interleukin-7-based identification of liver lymphatic endothelial cells reveals their unique structural features

Background & Aims

The lymphatic system plays crucial roles in maintaining fluid balance and immune regulation. Studying the liver lymphatics has been considered challenging, as common lymphatic endothelial cell (LyEC) markers are expressed by other liver cells. Additionally, isolation of sufficient numbers of LyECs has been challenging because of their extremely low abundance (<0.01% of entire liver cell population) in a normal liver.

Methods

Potential LyEC markers was identified using our published single-cell RNA sequencing (scRNA-seq) dataset (GSE147581) in mouse livers. Interleukin-7 (IL7) promoter-driven green fluorescent protein knock-in heterozygous mice were used for the validation of IL7 expression in LyECs in the liver, for the development of liver LyEC isolation protocol, and generating liver ischemia/reperfusion (I/R) injury. Scanning electron microscopy was used for the structural analysis of LyECs. Changes in LyEC phenotypes in livers of mice with I/R were determined by RNA-seq analysis.

Results

Through scRNA-seq analysis, we have identified IL7 as an exclusive marker for liver LyECs, with no overlap with other liver cell types. Based on IL7 expression in liver LyECs, we have established an LyEC isolation method and observed distinct cell surface structures of LyECs with fenestrae and cellular pores (ranging from 100 to 400 nm in diameter). Furthermore, we identified LyEC genes that undergo alterations during I/R liver injuries.

Conclusions

This study not only identified IL7 as an exclusively expressed gene in liver LyECs, but also enhanced our understanding of LyEC structures and demonstrated transcriptomic changes in injured livers.

Impact and implications

Understanding the lymphatic system in the liver is challenging because of the absence of specific markers for liver LyEC. This study has identified IL7 as a reliable marker for LyECs, enabling the development of an effective method for their isolation, elucidating their unique cell surface structure, and identifying LyEC genes that undergo changes during liver damage. The development of IL7 antibodies for detecting it in human liver specimens will further advance our understanding of the liver lymphatic system in the future.

Insights into the heterogeneity of iNKT cells: tissue-resident and circulating subsets shaped by local microenvironmental cues

Invariant natural killer T (iNKT) cells are a distinct subpopulation of innate-like T lymphocytes. They are characterized by semi-invariant T cell receptors (TCRs) that recognize both self and foreign lipid antigens presented by CD1d, a non-polymorphic MHC class I-like molecule. iNKT cells play a critical role in stimulating innate and adaptive immune responses, providing an effective defense against infections and cancers, while also contributing to chronic inflammation. The functions of iNKT cells are specific to their location, ranging from lymphoid to non-lymphoid tissues, such as the thymus, lung, liver, intestine, and adipose tissue. This review aims to provide insights into the heterogeneity of development and function in iNKT cells. First, we will review the expression of master transcription factors that define subsets of iNKT cells and their production of effector molecules such as cytokines and granzymes. In this article, we describe the gene expression profiles contributing to the kinetics, distribution, and cytotoxicity of iNKT cells across different tissue types. We also review the impact of cytokine production in distinct immune microenvironments on iNKT cell heterogeneity, highlighting a recently identified circulating iNKT cell subset. Additionally, we explore the potential of exploiting iNKT cell heterogeneity to create potent immunotherapies for human cancers in the future.

The role of natural killer T cells in liver transplantation

Natural killer T cells (NKTs) are innate-like lymphocytes that are abundant in the liver and participate in liver immunity. NKT cells express both NK cell and T cell markers, modulate innate and adaptive immune responses. Type I and Type II NKT cells are classified according to the TCR usage, while they recognize lipid antigen in a non-classical major histocompatibility (MHC) molecule CD1d-restricted manner. Once activated, NKT cells can quickly produce cytokines and chemokines to negatively or positively regulate the immune responses, depending on the different NKT subsets. In liver transplantation (LTx), the immune reactions in a series of processes determine the recipients' long-term survival, including ischemia-reperfusion injury, alloresponse, and post-transplant infection. This review provides insight into the research on NKT cells subpopulations in LTx immunity during different processes, and discusses the shortcomings of the current research on NKT cells. Additionally, the CD56-expressing T cells are recognized as a NK-like T cell population, they were also discussed during these processes.

Lung group 2 innate lymphoid cells differentially depend on local IL-7 for their distribution, activation, and maintenance in innate and adaptive immunity-mediated airway inflammation

Interleukin-7 (IL-7) is a cytokine critical for the development and maintenance of group 2 innate lymphoid cells (ILC2s). ILC2s are resident in peripheral tissues such as the intestine and lung. However, whether IL-7 produced in the lung plays a role in the maintenance and function of lung ILC2s during airway inflammation remains unknown. IL-7 was expressed in bronchoalveolar epithelial cells and lymphatic endothelial cells (LECs). To investigate the role of local IL-7 in lung ILC2s, we generated two types of IL-7 conditional knockout (IL-7cKO) mice: Sftpc-Cre (SPC-Cre) IL-7cKO mice specific for bronchial epithelial cells and type 2 alveolar epithelial cells and Lyve1-Cre IL-7cKO mice specific for LECs. In steady state, ILC2s were located near airway epithelia, although lung ILC2s were unchanged in the two lines of IL-7cKO mice. In papain-induced airway inflammation dependent on innate immunity, lung ILC2s localized near bronchia via CCR4 expression, and eosinophil infiltration and type 2 cytokine production were reduced in SPC-Cre IL-7cKO mice. In contrast, in house dust mite (HDM)-induced airway inflammation dependent on adaptive immunity, lung ILC2s localized near lymphatic vessels via their CCR2 expression 2 weeks after the last challenge. Furthermore, lung ILC2s were decreased in Lyve1-Cre IL-7cKO mice in the HDM-induced inflammation because of decreased cell survival and proliferation. Finally, administration of anti-IL-7 antibody attenuated papain-induced inflammation by suppressing the activation of ILC2s. Thus, this study demonstrates that IL-7 produced by bronchoalveolar epithelial cells and LECs differentially controls the activation and maintenance of lung ILC2s, where they are localized in airway inflammation.

Liver type 1 innate lymphoid cells lacking IL-7 receptor are a native killer cell subset fostered by parenchymal niches

Group 1 innate lymphoid cells (G1-ILCs), including circulating natural killer (NK) cells and tissue-resident type 1 ILCs (ILC1s), are innate immune sentinels critical for responses against infection and cancer. In contrast to relatively uniform NK cells through the body, diverse ILC1 subsets have been characterized across and within tissues in mice, but their developmental and functional heterogeneity remain unsolved. Here, using multimodal in vivo approaches including fate-mapping and targeting of the interleukin 15 (IL-15)-producing microenvironment, we demonstrate that liver parenchymal niches support the development of a cytotoxic ILC1 subset lacking IL-7 receptor (7 R^- ILC1s). During ontogeny, fetal liver (FL) G1-ILCs arise perivascularly and then differentiate into 7 R^- ILC1s within sinusoids. Hepatocyte-derived IL-15 supports parenchymal development of FL G1-ILCs to maintain adult pool of 7 R^- ILC1s. IL-7R⁺ (7R⁺) ILC1s in the liver, candidate precursors for 7 R^- ILC1s, are not essential for 7 R^- ILC1 development in physiological conditions. Functionally, 7 R^- ILC1s exhibit killing activity at steady state through granzyme B expression, which is underpinned by constitutive mTOR activity, unlike NK cells with exogenous stimulation-dependent cytotoxicity. Our study reveals the unique ontogeny and functions of liver-specific ILC1s, providing a detailed interpretation of ILC1 heterogeneity.

New insights into iNKT cells and their roles in liver diseases

Natural killer T cells (NKTs) are an important part of the immune system. Since their discovery in the 1990s, researchers have gained deeper insights into the physiology and functions of these cells in many liver diseases. NKT cells are divided into two subsets, type I and type II. Type I NKT cells are also named iNKT cells as they express a semi-invariant T cell-receptor (TCR) α chain. As part of the innate immune system, hepatic iNKT cells interact with hepatocytes, macrophages (Kupffer cells), T cells, and dendritic cells through direct cell-to-cell contact and cytokine secretion, bridging the innate and adaptive immune systems. A better understanding of hepatic iNKT cells is necessary for finding new methods of treating liver disease including autoimmune liver diseases, alcoholic liver diseases (ALDs), non-alcoholic fatty liver diseases (NAFLDs), and liver tumors. Here we summarize how iNKT cells are activated, how they interact with other cells, and how they function in the presence of liver disease.

Intestinal fibroblastic reticular cell niches control innate lymphoid cell homeostasis and function

Innate lymphoid cells (ILCs) govern immune cell homeostasis in the intestine and protect the host against microbial pathogens. Various cell-intrinsic pathways have been identified that determine ILC development and differentiation. However, the cellular components that regulate ILC sustenance and function in the intestinal lamina propria are less known. Using single-cell transcriptomic analysis of lamina propria fibroblasts, we identify fibroblastic reticular cells (FRCs) that underpin cryptopatches (CPs) and isolated lymphoid follicles (ILFs). Genetic ablation of lymphotoxin-β receptor expression in Ccl19-expressing FRCs blocks the maturation of CPs into mature ILFs. Interactome analysis shows the major niche factors and processes underlying FRC-ILC crosstalk. In vivo validation confirms that a sustained lymphotoxin-driven feedforward loop of FRC activation including IL-7 generation is critical for the maintenance of functional ILC populations. In sum, our study indicates critical fibroblastic niches within the intestinal lamina propria that control ILC homeostasis and functionality and thereby secure protective gut immunity.

Fibroblastic reticular cells (FRCs) support localisation of immune cells in secondary lymphoid tissues but less is known about the lamina propria. Here the authors use scRNA-seq and intestinal infection to characterise FRCs in the intestinal lamina propria and show specialised niches that foster innate lymphoid cells during homeostasis and infection.

In vivo availability of the cytokine IL-7 constrains the survival and homeostasis of peripheral iNKT cells

Understanding the homeostatic mechanism of invariant natural killer T (iNKT) cells is a critical issue in iNKT cell biology. Because interleukin (IL)-15 is required for the thymic generation of iNKT cells, IL-15 has also been considered necessary for the homeostasis of peripheral iNKT cells. Here, we delineated the in vivo cytokine requirement for iNKT cells, and we came to the surprising conclusion that IL-7, not IL-15, is the homeostatic cytokine for iNKT cells. Employing a series of experimental mouse models where the availability of IL-7 or IL-15 was manipulated in peripheral tissues, either by genetic tools or by adult thymectomy and cytokine pump installation, we demonstrate that the abundance of IL-7, and not IL-15, limits the size of the peripheral iNKT cell pool. These results redefine the cytokine requirement for iNKT cells and indicate competition for IL-7 between iNKT and conventional αβ T cells.

The Roles of IL-7 and IL-15 in Niches for Lymphocyte Progenitors and Immune Cells in Lymphoid Organs

Lymphoid organs consist of immune cells and stromal cells. The stromal cells produce various cytokines that support the development, maintenance, and response of the immune cells. IL-7 and IL-15 are the major cytokines produced by stromal cells and are essential for the development and maintenance of lymphocytes and innate lymphoid cells (ILCs). In addition, IL-7 is indispensable for the organogenesis of lymphoid organs. However, because the amount of these two cytokines is relatively low, it has been difficult to directly detect their expression. Recently, several groups succeeded in establishing IL-7 and IL-15 reporter mouse lines. As expected, IL-7 and IL-15 were detected in mesenchymal stromal cells in the bone marrow and lymph nodes and in epithelial cells in the thymus. Furthermore, IL-7 and IL-15 were differentially expressed in lymphatic endothelial cells and blood endothelial cells, respectively. In addition to their expression, many groups have analyzed the local functions of IL-7 and IL-15 by using cell-type-specific knockout mice. From these experiments, CXCL12-expressing mesenchymal stromal cells were identified as the major niche for early B cell precursors. Single-cell RNA sequencing (scRNA-seq) analysis has revealed different subpopulations of stromal cells in the lymphoid organs, including those that express both IL-7 and IL-15. Future research is still needed to elucidate which stromal cells serve as the niche for the early precursors of ILCs and NK cells in the bone marrow.

Identification of liver-specific CD24+ invariant NK T cells with low granzyme B production and high proliferative capacity

Invariant NK T (iNKT) cells are innate-like lymphocytes that can recognize the lipid Ag presented by MHC I like molecule CD1d. Distinct tissue distribution of iNKT cells subsets implies a contribution of these subsets to their related tissue regional immunity. iNKT cells are enriched in liver, an organ with unique immunological properties. Whether liver-specific iNKT cells exist and dedicate to the liver immunity remains elusive. Here, a liver-specific CD24⁺ iNKT subset is shown. Hepatic CD24⁺ iNKT cells show higher levels of proliferation, glucose metabolism, and mTOR activity comparing to CD24^- iNKT cells. Although CD24⁺ iNKT cells and CD24^- iNKT cells in the liver produce similar amounts of cytokines, the hepatic CD24⁺ iNKT cells exhibit lower granzyme B production. These liver-specific CD24⁺ iNKT cells are derived from thymus and differentiate into CD24⁺ iNKT in the liver microenvironment. Moreover, liver microenvironment induces the formation of CD24⁺ conventional T cells as well, and these cells exhibit higher proliferation ability but lower granzyme B production in comparison with CD24^- T cells. The results propose that liver microenvironment might induce the generation of liver-specific iNKT subset that might play an important role in maintaining liver homeostasis.

Genome-scale metabolic modelling of SARS-CoV-2 in cancer cells reveals an increased shift to glycolytic energy production

Cancer is considered a high‐risk condition for severe illness resulting from COVID‐19. The interaction between severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2) and human metabolism is key to elucidating the risk posed by COVID‐19 for cancer patients and identifying effective treatments, yet it is largely uncharacterised on a mechanistic level. We present a genome‐scale map of short‐term metabolic alterations triggered by SARS‐CoV‐2 infection of cancer cells. Through transcriptomic‐ and proteomic‐informed genome‐scale metabolic modelling, we characterise the role of RNA and fatty acid biosynthesis in conjunction with a rewiring in energy production pathways and enhanced cytokine secretion. These findings link together complementary aspects of viral invasion of cancer cells, while providing mechanistic insights that can inform the development of treatment strategies.

Single-cell analysis reveals the origins and intrahepatic development of liver-resident IFN-γ-producing γδ T cells

γδ T cells are heterogeneous lymphocytes located in various tissues. However, a systematic and comprehensive understanding of the origins of γδ T cell heterogeneity and the extrathymic developmental pathway associated with liver γδ T cells remain largely unsolved. In this study, we performed single-cell RNA sequencing (scRNA-seq) to comprehensively catalog the heterogeneity of γδ T cells derived from murine liver and thymus samples. We revealed the developmental trajectory of γδ T cells and found that the liver contains γδ T cell precursors (pre-γδ T cells). The developmental potential of hepatic γδ T precursor cells was confirmed through in vitro coculture experiments and in vivo adoptive transfer experiments. The adoptive transfer of hematopoietic progenitor Lin^-Sca-1⁺Mac-1⁺ (LSM) cells from fetal or adult liver samples to sublethally irradiated recipients resulted in the differentiation of liver LSM cells into pre-γδ T cells and interferon-gamma⁺ (IFN-γ⁺) but not interleukin-17a⁺ (IL-17a⁺) γδ T cells in the liver. Importantly, thymectomized mouse models showed that IFN-γ-producing γδ T cells could originate from liver LSM cells in a thymus-independent manner. These results suggested that liver hematopoietic progenitor LSM cells were able to differentiate into pre-γδ T cells and functionally mature γδ T cells, which implied that these cells are involved in a distinct developmental pathway independent of thymus-derived γδ T cells.

Invariant natural killer T cells: Not to be ignored in liver disease

The liver is an important immune organ. Hepatocellular injury can be caused by many factors, which further leads to chronic liver diseases by activating the immune system. Multiple immune cells, such as T lymphocytes, B lymphocytes, natural killer cells (NKs), natural killer T cells (NKTs), and γδT cells, accumulate and participate in the immune regulation of the liver. NKTs are an indispensable component of immune cells in the liver, and invariant natural killer T cells (iNKTs) are the main subpopulation of NKTs. iNKTs activated by glycolipid antigen presented on CD1d secrete a series of cytokines and also act on other immune cells through cell-to-cell contact. Studies on the relationship between iNKTs and liver immunity have provided clues to uncover the pathogenesis of liver diseases and develop a promising strategy for the diagnosis and treatment of liver diseases.

Immunopathobiology and therapeutic targets related to cytokines in liver diseases

Chronic liver injury with any etiology can progress to fibrosis and the end-stage diseases cirrhosis and hepatocellular carcinoma. The progression of liver disease is controlled by a variety of factors, including liver injury, inflammatory cells, inflammatory mediators, cytokines, and the gut microbiome. In the current review, we discuss recent data on a large number of cytokines that play important roles in regulating liver injury, inflammation, fibrosis, and regeneration, with a focus on interferons and T helper (Th) 1, Th2, Th9, Th17, interleukin (IL)-1 family, IL-6 family, and IL-20 family cytokines. Hepatocytes can also produce certain cytokines (such as IL-7, IL-11, and IL-33), and the functions of these cytokines in the liver are briefly summarized. Several cytokines have great therapeutic potential, and some are currently being tested as therapeutic targets in clinical trials for the treatment of liver diseases, which are also described.

Type 1 Innate Lymphoid Cells Protect Mice from Acute Liver Injury via Interferon-γ Secretion for Upregulating Bcl-xL Expression in Hepatocytes

Although type 1 innate lymphoid cells (ILC1s) have been originally found as liver-resident ILCs, their pathophysiological role in the liver remains poorly investigated. Here, we demonstrated that carbon tetrachloride (CCl₄) injection into mice activated ILC1s, but not natural killer (NK) cells, in the liver. Activated ILC1s produced interferon-γ (IFN-γ) and protected mice from CCl₄-induced acute liver injury. IFN-γ released from activated ILC1s promoted the survival of hepatocytes through upregulation of Bcl-xL. An activating NK receptor, DNAM-1, was required for the optimal activation and IFN-γ production of liver ILC1s. Extracellular adenosine triphosphate accelerated interleukin-12-driven IFN-γ production by liver ILC1s. These findings suggest that ILC1s are critical for tissue protection during acute liver injury.

Exploring the complex role of chemokines and chemoattractants in vivo on leukocyte dynamics

Chemotaxis is fundamental for leukocyte migration in immunity and inflammation and contributes to the pathogenesis of many human diseases. Although chemokines and various other chemoattractants were initially appreciated as important mediators of acute inflammation, in the past years they have emerged as critical mediators of cell migration during immune surveillance, organ development, and cancer progression. Such advances in our knowledge in chemokine biology have paved the way for the development of specific pharmacological targets with great therapeutic potential. Chemoattractants may belong to different classes, including a complex chemokine system of approximately 50 endogenous molecules that bind to G protein-coupled receptors, which are expressed by a wide variety of cell types. Also, an unknown number of other chemoattractants may be generated by pathogens and damaged/dead cells. Therefore, blocking chemotaxis without causing side effects is an extremely challenging task. In this review, we focus on recent advances in understanding how the chemokine system orchestrates immune cell migration and positioning at the whole organ level in homeostasis, inflammation, and infection.

Tissue-specific functions of invariant natural killer T cells

Invariant natural killer T cells (iNKT cells) are an innate-like T cell subset that expresses an invariant T cell receptor (TCR) α-chain and recognizes lipids presented on CD1d. They secrete diverse cytokines and can influence many types of immune responses. Despite having highly similar TCR specificities, iNKT cells differentiate in the thymus into distinct subsets that are analogous to T helper 1 (T_H1), T_H2 and T_H17 cell subsets. Additional iNKT cell subsets that may require peripheral activation have also been described, including one that produces IL-10. In general, iNKT cells are non-circulating, tissue-resident lymphocytes, but the prevalence of different iNKT cell subsets differs markedly between tissues. Here, we summarize the functions of iNKT cells in four tissues in which they are prevalent, namely, the liver, the lungs, adipose tissue and the intestine. Importantly, we explain how local iNKT cell responses at each site contribute to tissue homeostasis and protection from infection but can also contribute to tissue inflammation and damage.

Tissue-resident memory-like ILCs: innate counterparts of TRM cells

Innate lymphoid cells (ILCs) are defined as lymphocytes that lack RAG recombinase and do not express diverse antigen receptors; however, recent studies have revealed the adaptive features of ILCs. Mouse cytomegalovirus (MCMV)- and cytokine-induced memory natural killer (NK) cells circulate in the blood and are referred to as conventional memory NK cells. In contrast, virus- and hapten-induced memory NK cells, hapten-induced memory ILC1s, and cytokine-induced memory-like ILC2s exhibit long-term residency in the liver or lung, and are referred to as tissue-resident memory ILCs. Considering their similar migration patterns and memory potential, tissue-resident memory ILCs could be regarded as innate counterparts of resident memory T (T_RM) cells. Both tissue-resident memory ILCs and T_RM cells share common characteristics in terms of dynamics, phenotype, and molecular regulation. The emergence of ILC memory expands the basic biology of ILCs and prompts us to re-examine their functions in disease progression. This review discusses the evidence supporting tissue-resident memory NK cells and other memory ILC subsets, compares them with T_RM cells, and highlights key unsolved questions in this emerging field.

Innate lymphoid cell memory

Innate lymphoid cells (ILCs), including natural killer (NK) cells, ILC1s, ILC2s, ILC3s, and lymphoid tissue inducer (LTi) cells, comprise the first line of innate immune defense against pathogens and tumors. Over the past decade, accumulating evidence has demonstrated immunological memory in ILC subsets: for example, NK cells recall haptens, viruses, and cytokines; ILC1s recall haptens; and ILC2s recall cytokines. Although the development and functions of ILCs mirror those of T-cell subsets, ILC and T-cell memory exhibit both common characteristics and specific properties. Encouragingly, ILC memory has been found to confer benefits in long-term tumor control and vaccination, providing insight for novel memory ILC-based tumor immunotherapy and vaccine-development strategies. In this review, we discuss the evidence supporting ILC memory and present a comprehensive framework of the ILC memory system.

Memory formation and long-term maintenance of IL-7Rα+ ILC1s via a lymph node-liver axis

Natural killer (NK) cells are reported to have immunological memory, with CD49a⁺ liver-resident NK cells shown to confer hapten-specific memory responses, but how this memory is induced or maintained is unclear. Here we show that memory type I innate lymphoid cells (ILC1s), which express IL-7Rα, are generated in the lymph nodes (LNs) and require IL-7R signaling to maintain their longevity in the liver. Hapten sensitization initiates CXCR3-dependent recruitment of IL-7Rα⁺ ILC1s into skin-draining LNs, where they are primed and acquire hapten-specific memory potential. Memory IL-7Rα⁺ ILC1s then exit draining LNs and are preferentially recruited, via CXCR6, to reside in the liver. Moreover, long-term blockade of IL-7R signaling significantly reduces ILC1-mediated memory responses. Thus, our results identify a memory IL-7Rα⁺ ILC1 population and reveal a LN-liver axis that is essential for ILC1 memory generation and long-term maintenance.

Natural killer cells may respond better on second antigen encounters, but how this memory is induced or maintained in vivo is not clear. Here the authors show that memory NK cells expressing interleukin-7 (IL-7) receptor are induced in the lymph nodes but later recruited to liver for long term, IL-7 dependent survival and memory maintenance.

Role of Common γ-Chain Cytokines in Lung Interleukin-22 Regulation after Acute Exposure to Aspergillus fumigatus

Humans are constantly exposed to the opportunistic mold Aspergillus fumigatus, and disease caused by this pathogen is often determined by the magnitude of local and systemic immune responses. We have previously shown a protective role for interleukin-22 (IL-22) after acute A. fumigatus exposure. Here, employing IL-22^Cre R26R^eYFP reporter mice, we identified iNKT cells, γδ T cells, and type 3 innate lymphoid cells (ILC3s) as lung cell sources of IL-22 in response to acute A. fumigatus exposure. As these cells often utilize common γ-chain cytokines for their development or maintenance, we determined the role of IL-7, IL-21, and IL-15 in lung IL-22 induction and A. fumigatus lung clearance. We observed that IL-7, IL-21, and IL-15 were essential for, partially required for, or negatively regulated the production of IL-22, respectively. Deficiency in IL-7 and IL-21, but not IL-15R, resulted in impaired fungal clearance. Surprisingly, however, the absence of IL-7, IL-21, or IL-15R signaling had no effect on neutrophil recruitment. The levels of IL-1α, an essential anti-A. fumigatus proinflammatory cytokine, were increased in the absence of IL-7 and IL-15R but decreased in the absence of IL-21. IL-7 was responsible for maintaining lung iNKT cells and γδ T cells, whereas IL-21 was responsible for maintaining lung iNKT cells and ILC3s. In contrast, IL-15R deficiency had no effect on the absolute numbers of any IL-22 cell source, rather resulting in enhanced per cell production of IL-22 by iNKT cells and γδ T cells. Collectively, these results provide insight into how the IL-22 response in the lung is shaped after acute A. fumigatus exposure.

The common γ-chain cytokine IL-7 promotes immunopathogenesis during fungal asthma

Asthmatics sensitized to fungi are reported to have more severe asthma, yet the immunopathogenic pathways contributing to this severity have not been identified. In a pilot assessment of human asthmatics, those subjects sensitized to fungi demonstrated elevated levels of the common γ-chain cytokine IL-7 in lung lavage fluid, which negatively correlated with the lung function measurement PC20. Subsequently, we show that IL-7 administration during experimental fungal asthma worsened lung function and increased the levels of type 2 cytokines (IL-4, IL-5, IL-13), proallergic chemokines (CCL17, CCL22) and proinflammatory cytokines (IL-1α, IL-1β). Intriguingly, IL-7 administration also increased IL-22, which we have previously reported to drive immunopathogenic responses in experimental fungal asthma. Employing IL22CreR26ReYFP reporter mice, we identified γδ T cells, iNKT cells, CD4 T cells and ILC3s as sources of IL-22 during fungal asthma; however, only iNKT cells were significantly increased after IL-7 administration. IL-7-induced immunopathogenesis required both type 2 and IL-22 responses. Blockade of IL-7Rα in vivo resulted in attenuated IL-22 production, lower CCL22 levels, decreased iNKT cell, CD4 T-cell and eosinophil recruitment, yet paradoxically increased dynamic lung resistance. Collectively, these results suggest a complex role for IL-7 signaling in allergic fungal asthma.

Peripheral PDGFRα+gp38+ mesenchymal cells support the differentiation of fetal liver-derived ILC2

Group 2 innate lymphoid cells (ILC2s) are derived from common lymphoid progenitors (CLPs) via several specific precursors, and the transcription factors essential for ILC2 differentiation have been extensively studied. However, the external factors regulating commitment to the ILC lineage as well as the sites and stromal cells that constitute the optimal microenvironment for ILC2-specific differentiation are not fully defined. In this study, we demonstrate that three key external factors, the concentration of interleukin 7 (IL-7) and strength and duration of Notch signaling, coordinately determine the fate of CLP toward the T, B, or ILC lineage. Additionally, we identified three stages of ILC2 in the fetal mesentery that require STAT5 signals for maturation: ILC progenitors, CCR9⁺ ILC2 progenitors, and KLRG1^- immature ILC2. We further demonstrate that ILC2 development is supported by mesenteric platelet-derived growth factor receptor α (PDGFRα)⁺ glycoprotein 38 (gp38)⁺ mesenchymal cells. Collectively, our results suggest that early differentiation of ILC2 occurs in the fetal liver via IL-7 and Notch signaling, whereas final differentiation occurs in the periphery with the aid of PDGFRα⁺gp38⁺ cells.

Interleukin-7 Regulates T Follicular Helper Cell Function in Patients with Chronic Hepatitis C

Signaling through interleukin (IL)-7 is essential and required for development, differentiation, proliferation, and homeostasis of T cells. However, the role of IL-7 in regulation of CD4⁺ T cells in chronic viral infections was not fully elucidated. Thus, the aim of the current study was to investigate the immunomodulatory activity of IL-7 to T follicular helper (Tfh) cells and its contribution to pathogenesis of chronic HCV, hepatitis C virus (HCV) infection. A total of 47 patients with chronic hepatitis C and 19 normal controls were enrolled. Serum IL-7 and proportion of Tfh cells was measured. The regulatory function of IL-7 to Tfh cells was also investigated in CD4⁺ T cells and CD4⁺ T/HCVcc-infected Huh7.5 cell cocultured system. Serum IL-7 concentration was significantly downregulated in patients with chronic hepatitis C, and was negatively correlated with HCV RNA level. Tfh frequency and Tfh-associated cytokines (IL-21 and IL-6) were also reduced in chronic HCV-infected patients. Moreover, recombinant IL-7 stimulation elevated proportion of Tfh cells and IL-21/IL-6 secretion in both HCV-specific and nonspecific manners. Furthermore, IL-7-treated CD4⁺ T cells exhibited elevated antiviral activities without killing infected hepatocytes, which presented as inhibition of HCV RNA, induction of antiviral proteins, and promotion of cytokine production (especially IL-21) in cocultured system. This process might be dependent on IL-6 secretion. The current data revealed that IL-7 regulated HCV-specific and nonspecific activated Tfh cells, which might contribute to viral clearance. IL-7 could be a potential therapeutic agent for the treatment of chronic hepatitis C.

Critical Role for Very-Long Chain Sphingolipids in Invariant Natural Killer T Cell Development and Homeostasis

The role of sphingolipids (SLs) in the immune system has come under increasing scrutiny recently due to the emerging contributions that these important membrane components play in regulating a variety of immunological processes. The acyl chain length of SLs appears particularly critical in determining SL function. Here, we show a role for very-long acyl chain SLs (VLC-SLs) in invariant natural killer T (iNKT) cell maturation in the thymus and homeostasis in the liver. Ceramide synthase 2-null mice, which lack VLC-SLs, were susceptible to a hepatotropic strain of lymphocytic choriomeningitis virus, which is due to a reduction in the number of iNKT cells. Bone marrow chimera experiments indicated that hematopoietic-derived VLC-SLs are essential for maturation of iNKT cells in the thymus, whereas parenchymal-derived VLC-SLs are crucial for iNKT cell survival and maintenance in the liver. Our findings suggest a critical role for VLC-SL in iNKT cell physiology.

A novel deletion mutation in IL2RG gene results in X-linked severe combined immunodeficiency with an atypical phenotype

Severe combined immunodeficiency (SCID) is the most serious disorder among primary immunodeficiency diseases threatening children's life. Atypical SCID variant, presenting with mild reduced T cells subsets, is often associated with infection susceptibility but poor clinical diagnosis. The atypical X-SCID patient in the present study showed a mild clinical presentation with a T^lowNK⁺B⁺ immunophenotype. The patient has reduced T- cell subpopulations with a subdued thymic output measured by sjTRECs. Further analysis showed that T cells maintained a normal proliferation and a broad Vβ repertoire. NK cells, however, exhibited a skewed development toward immature CD3^-CD16⁺CD56^- cells. Genetic analysis revealed a novel deletion at nucleotide 52 in exon 1 of IL2RG gene. Sequence alignment predicted a truncated IL2RG protein missing signal peptide derived from a possible alternative reading frame. The novel mutation in IL2RG gene identified in our study may help the early diagnosis of atypical X-SCID.

Notch Signaling Regulates the Homeostasis of Tissue-Restricted Innate-like T Cells

Although Notch signaling plays important roles in lineage commitment and differentiation of multiple cell types including conventional T cells, nothing is currently known concerning Notch function in innate-like T cells. We have found that the homeostasis of several well-characterized populations of innate-like T cells including invariant NKT cells (iNKT), CD8ααTCRαβ small intestinal intraepithelial lymphocytes, and innate memory phenotype CD8 T cells is controlled by Notch. Notch selectively regulates hepatic iNKT cell survival via tissue-restricted control of B cell lymphoma 2 and IL-7Rα expression. More generally, Notch regulation of innate-like T cell homeostasis involves both cell-intrinsic and -extrinsic mechanisms and relies upon context-dependent interactions with Notch ligand-expressing fibroblastic stromal cells. Collectively, using conditional ablation of Notch receptors on peripheral T cells or Notch ligands on putative fibroblastic stromal cells, we show that Notch signaling is indispensable for the homeostasis of three tissue-restricted populations of innate-like T cells: hepatic iNKT, CD8ααTCRαβ small intestinal intraepithelial lymphocytes, and innate memory phenotype CD8 T cells, thus supporting a generalized role for Notch in innate T cell homeostasis.

Thy1+IL-7+ lymphatic endothelial cells in iBALT provide a survival niche for memory T-helper cells in allergic airway inflammation

Memory CD4(+) T helper (Th) cells are central to long-term protection against pathogens, but they can also be pathogenic and drive chronic inflammatory disorders. How these pathogenic memory Th cells are maintained, particularly at sites of local inflammation, remains unclear. We found that ectopic lymphoid-like structures called inducible bronchus-associated lymphoid tissue (iBALT) are formed during chronic allergic inflammation in the lung, and that memory-type pathogenic Th2 (Tpath2) cells capable of driving allergic inflammation are maintained within the iBALT structures. The maintenance of memory Th2 cells within iBALT is supported by Thy1(+)IL-7-producing lymphatic endothelial cells (LECs). The Thy1(+)IL-7-producing LECs express IL-33 and T-cell-attracting chemokines CCL21 and CCL19. Moreover, ectopic lymphoid structures consisting of memory CD4(+) T cells and IL-7(+)IL-33(+) LECs were found in nasal polyps of patients with eosinophilic chronic rhinosinusitis. Thus, Thy1(+)IL-7-producing LECs control chronic allergic airway inflammation by providing a survival niche for memory-type Tpath2 cells.

Hair follicle-derived IL-7 and IL-15 mediate skin-resident memory T cell homeostasis and lymphoma

The skin harbors a variety of resident leukocyte subsets that must be tightly regulated to maintain immune homeostasis. Hair follicles are unique structures in the skin that contribute to skin dendritic cell homeostasis via chemokine production. We demonstrate that CD4⁺ and CD8⁺ skin resident memory T cells (T_RM), responsible for long-term skin immunity, resided predominantly within the hair follicle epithelium of unperturbed epidermis. T_RM tropism for the epidermis and follicles was herein termed epidermotropism. Hair follicle-derived IL-15 was required for CD8⁺ T_RM, and IL-7 for CD8⁺ and CD4⁺ T_RM, to exert epidermotropism. The lack of either cytokine impaired hapten-induced contact hypersensitivity responses. In a model of cutaneous T cell lymphoma, epidermotropic CD4⁺ T_RM lymphoma cell localization depended on hair follicle-derived IL-7. These findings implicate hair follicle-derived cytokines as regulators of malignant and non-malignant T_RM cell tissue residence and suggest they may be targeted therapeutically in inflammatory skin disease and lymphoma.

STAT5 Orchestrates Local Epigenetic Changes for Chromatin Accessibility and Rearrangements by Direct Binding to the TCRγ Locus

The transcription factor STAT5, which is activated by IL-7R, controls chromatin accessibility and rearrangements of the TCRγ locus. Although STAT-binding motifs are conserved in Jγ promoters and Eγ enhancers, little is known about their precise roles in rearrangements of the TCRγ locus in vivo. To address this question, we established two lines of Jγ1 promoter mutant mice: one harboring a deletion in the Jγ1 promoter, including three STAT motifs (Jγ1P(Δ/Δ)), and the other carrying point mutations in the three STAT motifs in that promoter (Jγ1P(mS/mS)). Both Jγ1P(Δ/Δ) and Jγ1P(mS/mS) mice showed impaired recruitment of STAT5 and chromatin remodeling factor BRG1 at the Jγ1 gene segment. This resulted in severe and specific reduction in germline transcription, histone H3 acetylation, and histone H4 lysine 4 methylation of the Jγ1 gene segment in adult thymus. Rearrangement and DNA cleavage of the segment were severely diminished, and Jγ1 promoter mutant mice showed profoundly decreased numbers of γδ T cells of γ1 cluster origin. Finally, compared with controls, both mutant mice showed a severe reduction in rearrangements of the Jγ1 gene segment, perturbed development of γδ T cells of γ1 cluster origin in fetal thymus, and fewer Vγ3(+) dendritic epidermal T cells. Furthermore, interaction with the Jγ1 promoter and Eγ1, a TCRγ enhancer, was dependent on STAT motifs in the Jγ1 promoter. Overall, this study strongly suggests that direct binding of STAT5 to STAT motifs in the Jγ promoter is essential for local chromatin accessibility and Jγ/Eγ chromatin interaction, triggering rearrangements of the TCRγ locus.

Association between IL7R polymorphisms and severe liver disease in HIV/HCV coinfected patients: a cross-sectional study

BACKGROUND

Interleukin-7 (IL-7) is a critical factor for T cell development and for maintaining and restoring homeostasis of mature T cells. Polymorphisms at α-chain of the IL-7 receptor (IL7R or CD127) gene are related to evolution of HIV-infection, but there are no data concerning the evolution of hepatitis C virus (HCV) infection. The aim of this study was to analyze the association between IL7R polymorphisms and severe liver disease in HCV/HIV coinfected patients.

METHODS

We performed a cross-sectional study in 220 naïve patients who underwent a liver biopsy. IL7R polymorphisms (rs6897932, rs987106 and rs3194051) were genotyped using the GoldenGate(®) assay. The outcome variables were: (a) liver biopsy: advanced fibrosis (F ≥ 3), severe activity grade (A3); (b) non-invasive indexes: advanced fibrosis (APRI ≥1.5 and FIB-4 ≥3.25). Logistic regression analysis was used to investigate the association between IL7R polymorphisms and outcome variables. This test gives the differences between groups and the odds ratio (OR) for liver disease.

RESULTS

Patients with rs6897932 CC genotype had higher likelihood of having A3 than patients with rs6897932 CT/TT (adjusted odds ratio (aOR) = 4.16; p = 0.026). Patients with rs987106 TT genotype had higher odds of having F ≥ 3 (aOR = 3.09; p = 0.009) than rs987106 AA/AT carriers. Finally, patients with rs3194051 AA genotype had higher odds of having severe liver fibrosis (F ≥ 3; APRI ≥1.5, and FIB4 ≥3.25) than patients with rs3194051 AG/GG genotype [aOR = 2.73 (p = 0.010); aOR = 2.52 (p = 0.029); and aOR = 4.01 (p = 0.027); respectively]. The CTA haplotype (comprised of rs6897932, rs987106, and rs3194051) carriers had higher odds of having F ≥ 3 (aOR = 1.85; p = 0.012), APRI ≥1.5 (aOR = 1.94; p = 0.023), and FIB4 ≥3.25 (aOR = 2.47; p = 0.024). Conversely, the CAG haplotype carriers had lower odds of having F ≥ 3 (aOR = 0.48; p = 0.011), APRI ≥1.5 (aOR = 0.48; p = 0.029), and FIB4 ≥3.25 (aOR = 0.29; p = 0.010).

CONCLUSIONS

The presence of IL7R polymorphisms seems to be related to severe liver disease in HIV/HCV coinfected patients, because patients with unfavorable IL7R genotypes (rs6897932 CC, rs987106 TT, and rs3194051AA) had a worse prognosis of CHC.

Making Blood: The Haematopoietic Niche throughout Ontogeny

Approximately one-quarter of all cells in the adult human body are blood cells. The haematopoietic system is therefore massive in scale and requires exquisite regulation to be maintained under homeostatic conditions. It must also be able to respond when needed, such as during infection or following blood loss, to produce more blood cells. Supporting cells serve to maintain haematopoietic stem and progenitor cells during homeostatic and pathological conditions. This coalition of supportive cell types, organised in specific tissues, is termed the haematopoietic niche. Haematopoietic stem and progenitor cells are generated in a number of distinct locations during mammalian embryogenesis. These stem and progenitor cells migrate to a variety of anatomical locations through the conceptus until finally homing to the bone marrow shortly before birth. Under stress, extramedullary haematopoiesis can take place in regions that are typically lacking in blood-producing activity. Our aim in this review is to examine blood production throughout the embryo and adult, under normal and pathological conditions, to identify commonalities and distinctions between each niche. A clearer understanding of the mechanism underlying each haematopoietic niche can be applied to improving ex vivo cultures of haematopoietic stem cells and potentially lead to new directions for transplantation medicine.

The transcriptional programs of iNKT cells

Invariant natural killer T (iNKT) cells are innate T cells that express a semi-invariant T cell receptor (TCR) and recognize lipid antigens presented by CD1d molecules. As part of innate immunity, iNKT cells rapidly produce large amounts of cytokines after activation and regulate the function of innate and adaptive immune cells in antimicrobial immunity, tumor rejection and inflammatory diseases. Global transcriptional profiling has advanced our understanding of all aspects of iNKT cell biology. In this review, we discuss transcriptional analyses of iNKT cell development, functional subsets of iNKT cells, and global comparisons of iNKT cells to other innate and adaptive immune cells. Global transcriptional analysis revealed that iNKT cells have a transcriptional profile distinct from NK cells and MHC-restricted T cells, both during thymic development and in the periphery. The transcription factors EGR2 and PLZF (and microRNA like miR-150) are key regulators of the iNKT cell transcriptome during development. PLZF is one of several factors that control the homing and maintenance of organ-specific iNKT cell populations. As in MHC-restricted T cells, specific transcription factors are characteristic of functional subsets of iNKT cells, such as the transcription factor T-bet in the NKT1 subset. Exciting future directions for global transcriptional analyses include iNKT cells in disease models, diverse NKT cells and human studies.

Interleukin-7 is produced by afferent lymphatic vessels and supports lymphatic drainage

The cytokine interleukin (IL)-7 exerts essential roles in lymph node (LN) organogenesis and lymphocyte development and homeostasis. Recent studies have identified lymphatic endothelial cells (LECs) as a major source of IL-7 in LNs. Here, we report that LECs not only produce IL-7, but also express the IL-7 receptor chains IL-7Rα and CD132. Stimulation with recombinant IL-7 enhanced LEC in vitro activity and induced lymphangiogenesis in the cornea of wild-type (WT) mice. Whereas in IL-7Rα(-/-) mice, dermal lymphatic vessels (LVs) were abnormally organized and lymphatic drainage was compromised, transgenic overexpression of IL-7 in mice resulted in an expanded dermal LV network with increased drainage function. Moreover, systemic treatment with recombinant IL-7 enhanced lymphatic drainage in the skin of WT mice and of mice devoid of lymphocytes. Experiments in IL-7Rα(-/-) bone marrow chimeras demonstrated that the drainage-enhancing activity of IL-7 was exclusively dependent on IL-7Rα expression in stromal but not in hematopoietic cells. Finally, near-infrared in vivo imaging performed in IL-7Rα(-/-) mice revealed that the pumping activity of collecting vessels was normal but fluid uptake into lymphatic capillaries was defective. Overall, our data point toward an unexpected new role for IL-7 as a potential autocrine mediator of lymphatic drainage.

IL-7 produced by thymic epithelial cells plays a major role in the development of thymocytes and TCRγδ+ intraepithelial lymphocytes

IL-7 is a cytokine essential for T cell development and survival. However, the local function of IL-7 produced by thymic epithelial cells (TECs) is poorly understood. To address this question, we generated IL-7-floxed mice and crossed them with FoxN1 promoter-driven Cre (FoxN1-Cre) mice to establish knockout mice conditionally deficient for the expression of IL-7 by TECs. We found that αβ and γδ T cells were significantly reduced in the thymus of IL-7(f/f) FoxN1-Cre mice. Proportion of mature single-positive thymocytes was increased. In lymph nodes and the spleen, the numbers of T cells were partially restored in IL-7(f/f) FoxN1-Cre mice. In addition, γδ T cells were absent from the fetal thymus and epidermis of IL-7(f/f) FoxN1-Cre mice. Furthermore, TCRγδ(+) intraepithelial lymphocytes (IELs) were significantly decreased in the small intestines of IL-7(f/f) FoxN1-Cre mice. To evaluate the function of IL-7 produced in the intestine, we crossed the IL-7(f/f) mice with villin promoter-driven Cre (Vil-Cre) mice to obtain the mice deficient in IL-7 production from intestinal epithelial cells. We observed that αβ and γδ IELs of IL-7(f/f) Vil-Cre mice were comparable to control mice. Collectively, our results suggest that TEC-derived IL-7 plays a major role in proliferation, survival, and maturation of thymocytes and is indispensable for γδ T cell development. This study also demonstrates that IL-7 produced in the thymus is essential for the development of γδ IELs and indicates the thymic origin of γδ IELs.