Differential phenotypic and functional properties of liver-resident NK cells and mucosal ILC1s

High CD49a+ NK cell infiltrate is associated with poor clinical outcomes in Hepatocellular Carcinoma

NK cells infiltrating Hepatocellular Carcinoma (HCC) may express residency markers such as Integrin Subunit Alpha 1 (CD49a) that have been associated with nurturing functions in the decidua, and characterized by the production of angiogenic factors as well as loss of cytotoxicity. CIBERSORT, a computational analysis method for quantifying cell fractions from bulk tissue gene expression profiles, was used to estimate the infiltrating immune cell composition of the tumor microenvironment from gene expression profiles of a large cohort of 225 HCCs in the public GEO database. Decidual-like CD49a+ NK cells, in addition to another 22 immune cell populations, were characterized and thoroughly investigated so that HCC cell heterogeneity in a large cohort of 225 HCCs from the public GEO database could be studied. An inverse correlation of the expression of CD49a+ NK-cells and CD8+ T-cells suggested a negative association with clinical outcomes. This result was confirmed in a further validation cohort of 100 HCC patients from The Cancer Genome Atlas, Liver Hepatocellular Carcinoma (TCGA-LIHC). Cox regression analysis did not identify CD49a+ cells as a variable independently associated with survival. However, a more abundant infiltrate of this subset was present in patients at a more advanced pathological and clinical HCC stage. In conclusion, we found that NK cells, with a decidual-like gene expression profile, are enriched in HCC, and their abundance increases not only in tumor size but also at advanced stages of the disease suggesting that these cells play a role in tumor growth. For this reason, these NK cells may represent a possible new target for immunotherapeutic approaches in HCC.

Genetic distinction between functional tissue-resident and conventional natural killer cells

Tissue-residential natural killer (trNK) cells act as pioneering responders during infectious challenges. However, their discrimination with conventional NK (cNK) cells is still an issue. Through an integrative transcriptome comparison of the two NK subgroups from different tissues, we have defined two genesets capable of efficiently distinguishing them. Based on the two genesets, a fundamental difference between the activation of trNK and cNK is identified and further confirmed. Mechanistically, we have discovered a particular role of chromatin landscape in regulating the trNK activation. In addition, IL-21R and IL-18R are respectively highly expressed by trNK and cNK, indicating a role of cytokine milieu in determining their differential activation. Indeed, IL-21 is particularly critical in accessorily promoting trNK activation using a bunch of bifunctional transcription factors. Together, this study sheds light on the bona fide difference between trNK and cNK, which will further expand our knowledge about their distinct functionalities during immune responses.

ILC1: Development, maturation, and transcriptional regulation

Type 1 Innate Lymphoid cells (ILC1s) are tissue-resident cells that partake in the regulation of inflammation and homeostasis. A major feature of ILC1s is their ability to rapidly respond after infections. The effector repertoire of ILC1s includes the pro-inflammatory cytokines IFN-γ and TNF-α and cytotoxic mediators such as granzymes, which enable ILC1s to establish immune responses and to directly kill target cells. Recent advances in the characterization of ILC1s have considerably furthered our understanding of ILC1 development and maintenance in tissues. In particular, it has become clear how ILC1s operate independently from conventional natural killer cells, with which they share many characteristics. In this review, we discuss recent developments with regards to the differentiation, polarization, and effector maturation of ILC1s. These processes may underlie the observed heterogeneity in ILC1 populations within and between different tissues. Next, we highlight transcriptional programs that control each of the separate steps in the differentiation of ILC1s. These transcriptional programs are shared with other tissue-resident type-1 lymphocytes, such as tissue-resident memory T cells (T_RM ) and invariant natural killer T cells (iNKT), highlighting that ILC1s utilize networks of transcriptional regulation that are conserved between lymphocyte lineages to respond effectively to tissue-invading pathogens.

Innate immunity and early liver inflammation

The innate system constitutes a first-line defence mechanism against pathogens. 80% of the blood supply entering the human liver arrives from the splanchnic circulation through the portal vein, so it is constantly exposed to immunologically active substances and pathogens from the gastrointestinal tract. Rapid neutralization of pathogens and toxins is an essential function of the liver, but so too is avoidance of harmful and unnecessary immune reactions. This delicate balance of reactivity and tolerance is orchestrated by a diverse repertoire of hepatic immune cells. In particular, the human liver is enriched in many innate immune cell subsets, including Kupffer cells (KCs), innate lymphoid cells (ILCs) like Natural Killer (NK) cells and ILC-like unconventional T cells - namely Natural Killer T cells (NKT), γδ T cells and Mucosal-associated Invariant T cells (MAIT). These cells reside in the liver in a memory-effector state, so they respond quickly to trigger appropriate responses. The contribution of aberrant innate immunity to inflammatory liver diseases is now being better understood. In particular, we are beginning to understand how specific innate immune subsets trigger chronic liver inflammation, which ultimately results in hepatic fibrosis. In this review, we consider the roles of specific innate immune cell subsets in early inflammation in human liver disease.

Prospects for NK-based immunotherapy of chronic HBV infection

Effective and long-term treatment is required for controlling chronic Hepatitis B Virus (HBV) infection. Natural killer (NK) cells are antiviral innate lymphocytes and represent an essential arm of current immunotherapy. In chronic HBV (CHB), NK cells display altered changes in phenotypes and functions, but preserve antiviral activity, especially for cytolytic activity. On the other hand, NK cells might also cause liver injury in the disease. NK -based immunotherapy, including adoptive NK cell therapy and NK -based checkpoint inhibition, could potentially exploit the antiviral aspect of NK cells for controlling CHB infection while preventing liver tissue damage. Here, we review recent progress in NK cell biology under the context of CHB infection, and discuss potential NK -based immunotherapy strategies for the disease.

Immune-metabolic interactions in homeostasis and the progression to NASH

The incidence of non-alcoholic fatty liver disease (NAFLD) has increased significantly over the past two decades. NAFLD ranges from simple steatosis (NAFL) to nonalcoholic steatohepatitis (NASH) and predisposes to fibrosis and hepatocellular carcinoma (HCC). The importance of the immune system in hepatic physiology and in the progression of NAFLD is increasingly recognized. At homeostasis, the liver participates in immune defense against pathogens and in tolerance of gut-derived microbial compounds. Hepatic immune cells also respond to metabolic stimuli and have a role in NAFLD progression to NASH. In this review, we discuss how metabolic perturbations affect immune cell phenotype and function in NAFL and NASH, and then focus on the role of immune cells in liver homeostasis and in the development of NASH.

Type 1 Innate Lymphoid Cells Are Proinflammatory Effector Cells in Ischemia-Reperfusion Injury of Steatotic Livers

Innate lymphoid cells (ILCs), the most recently described family of lymphoid cells, play fundamental roles in tissue homeostasis through the production of key cytokine. Group 1 ILCs, comprised of conventional natural killer cells (cNKs) and type 1 ILCs (ILC1s), have been implicated in regulating immune-mediated inflammatory diseases. However, the role of ILC1s in nonalcoholic fatty liver disease (NAFLD) and ischemia-reperfusion injury (IRI) is unclear. Here, we investigated the role of ILC1 and cNK cells in a high-fat diet (HFD) murine model of partial warm IRI. We demonstrated that hepatic steatosis results in more severe IRI compared to non-steatotic livers. We further elicited that HFD-IRI mice show a significant increase in the ILC1 population, whereas the cNK population was unchanged. Since ILC1 and cNK are major sources of IFN-γ and TNF-α, we measured the level of ex vivo cytokine expression in normal diet (ND)-IRI and HFD-IRI conditions. We found that ILC1s in HFD-IRI mice produce significantly more IFN-γ and TNF-α when compared to ND-IRI. To further assess whether ILC1s are key proinflammatory effector cells in hepatic IRI of fatty livers, we studied both Rag1−/− mice, which possess cNK cells, and a substantial population of ILC1s versus the newly generated Rag1−/−Tbx21−/− double knockout (Rag1-Tbet DKO) mice, which lack type 1 ILCs, under HFD IRI conditions. Importantly, HFD Rag1-Tbet DKO mice showed significant protection from hepatic injury upon IRI when compared to Rag1−/− mice, suggesting that T-bet-expressing ILC1s play a role, at least in part, as proinflammatory effector cells in hepatic IRI under steatotic conditions.

The Functional Diversity of Tissue-Resident Natural Killer Cells Against Infection

For decades, studies of natural killer (NK) cells have focused on those found in peripheral blood (PBNK cells) as the prototype for NK cell biology. Only recently have researchers begun to explore the diversity of tissue-resident NK (tr-NK) cells. While tr-NK cells were initially identified from mice parabiosis and intravascular staining experiments, they can also be identified by tissue retention markers such as CD69, CD103, and others. More importantly, tr-NK cells have distinct functions compared to PBNK cells. Within the liver, there are diverse subsets of tr-NK cells expressing different combinations of tissue-retention markers and transcription factors, the clinical relevance of which are still unclear. Functionally, liver tr-NK are primed with immediate responsiveness to infection and equipped with regulatory mechanisms to prevent liver damage. When decidual NK (dNK) cells were first discovered, they were mainly characterized by their reduced cytotoxicity and functions related to placental development. Recent studies, however, revealed different mechanisms by which dNK cells prevent uterine infections. The lungs are one of the most highly exposed sites for infection due to their role in oxygen exchange. Upon influenza infection, lung tr-NK cells can degranulate and produce more inflammatory cytokines than PBNK cells. Less understood are gut tr-NK cells which were recently characterized in infants and adults for their functional differences. In this mini-review, we aim to provide a brief overview of the most recent discoveries on how several tr-NK cells are implicated in the immune response against infection. This article is protected by copyright. All rights reserved.

Crosstalk between NK cells and hepatic stellate cells in liver fibrosis (Review)

Liver fibrosis is a common pathological process of chronic liver diseases, including viral hepatitis and alcoholic liver disease, and ultimately progresses to irreversible cirrhosis and cancer. Hepatic stellate cells (HSCs) are activated to produce amounts of collagens in response to liver injury, thus triggering the initiation and progression of fibrogenesis. Natural killer (NK) cells serve as the essential component of hepatic innate immunity and are considered to alleviate fibrosis by killing activated HSCs. Current antifibrotic interventions have improved fibrosis, but fail to halt its progression in the advanced stage. Clarifying the interaction between NK cells and HSCs will provide clues to the pathogenesis and potential therapies for advanced liver fibrosis.

Requirement of RORα for maintenance and antitumor immunity of liver-resident natural killer cells/ILC1s

BACKGROUD AND AIMS

Liver type 1 innate lymphoid cells (ILC1s), also known as liver-resident natural killer (LrNK) cells, comprise a high proportion of total hepatic ILCs. However, factors regulating their maintenance and function remain unclear.

APPROACH AND RESULTS

In this study, we found high expression of retinoid-related orphan nuclear receptor alpha (RORα) in LrNK cells/ILC1s. Mice with conditional ablation of retinoid-related orphan nuclear receptor alpha (Rorα) in LrNK cells/ILC1s and conventional natural killer (cNK) cells had decreased LrNK cells/ILC1s but normal numbers of cNK cells. RORα-deficient LrNK cells/ILC1s displayed increased apoptosis and significantly altered transcriptional profile. Using a murine model of colorectal cancer liver metastasis, we found that RORα conditional deficiency resulted in more aggressive liver tumor progression and impaired effector molecule expression in LrNK cells/ILC1s. Consequently, treatment with the RORα agonist efficiently limited liver metastases and promoted effector molecule expression of LrNK cells/ILC1s.

CONCLUSIONS

This study reveals a role of RORα in LrNK cell/ILC1 maintenance and function, providing insights into the harnessing of LrNK cell/ILC1 activity in the treatment of liver cancer.

Ly49E separates liver ILC1s into embryo-derived and postnatal subsets with different functions

Type 1 innate lymphoid cells (ILC1s) represent the predominant population of liver ILCs and function as important effectors and regulators of immune responses, but the cellular heterogeneity of ILC1s is not fully understood. Here, single-cell RNA sequencing and flow cytometric analysis demonstrated that liver ILC1s could be dissected into Ly49E⁺ and Ly49E⁻ populations with unique transcriptional and phenotypic features. Genetic fate-mapping analysis revealed that liver Ly49E⁺ ILC1s with strong cytotoxicity originated from embryonic non–bone marrow hematopoietic progenitor cells (HPCs), persisted locally during postnatal life, and mediated protective immunity against cytomegalovirus infection in newborn mice. However, Ly49E⁻ ILC1s developed from BM and extramedullary HPCs after birth, gradually replaced Ly49E⁺ ILC1s in the livers with age, and contained the memory subset in recall response to hapten challenge. Thus, our study shows that Ly49E dissects liver ILC1s into two unique subpopulations, with distinct origins and a bias toward neonatal innate or adult immune memory responses.

Extracellular matrix proteins regulate NK cell function in peripheral tissues

Natural killer (NK) cells reject major histocompatibility complex class I (MHC-I)-deficient bone marrow through direct cytotoxicity but not solid organ transplants devoid of MHC-I. Here, we demonstrate an immediate switch in NK cell function upon exit from the circulation, characterized by a shift from direct cytotoxicity to chemokine/cytokine production. In the skin transplant paradigm, combining an NK cell-specific activating ligand, m157, with missing self MHC-I resulted in complete graft rejection, which was dependent on NK cells as potential helpers and T cells as effectors. Extracellular matrix proteins, collagen I, collagen III, and elastin, blocked NK cell cytotoxicity and promoted their chemokine/cytokine production. NK cell cytotoxicity against MHC-I-deficient melanoma in the skin was markedly increased by blocking tumor collagen deposition. MHC-I down-regulation occurred in solid human cancers but not leukemias, which could be directly targeted by circulating cytotoxic NK cells. Our findings uncover a fundamental mechanism that restricts direct NK cell cytotoxicity in peripheral tissues.

Natural killer cell‑based immunotherapy for lung cancer: Challenges and perspectives (Review)

Despite the marked success of molecular targeted therapy in lung cancer in this era of personalized medicine, its efficacy has been limited by the presence of resistance mechanisms. The prognosis of patients with lung cancer remains poor, and there is an unmet need to develop more effective therapies to improve clinical outcomes. The increasing insight into the human immune system has led to breakthroughs in immunotherapy and has prompted research interest in employing immunotherapy to treat lung cancer. Natural killer (NK) cells, which serve as the first line of defense against tumors, can induce the innate and adaptive immune responses. Therefore, the use of NK cells for the development of novel lung-cancer immunotherapy strategies is promising. A growing number of novel approaches that boost NK cell antitumor immunity and expand NK cell populations ex vivo now provide a platform for the development of antitumor immunotherapy. The present review outlined the biology of NK cells, summarized the role of NK cells in lung cancer and the effect of the tumor microenvironment on NK cells, highlighted the potential of NK cell-based immunotherapy as an effective therapeutic strategy for lung cancer and discussed future directions.

Natural Killer Cells and Type 1 Innate Lymphoid Cells in Hepatocellular Carcinoma: Current Knowledge and Future Perspectives

Natural killer (NK) cells and type 1 innate lymphoid cells (ILC1) are specific innate lymphoid cell subsets that are key for the detection and elimination of pathogens and cancer cells. In liver, while they share a number of characteristics, they differ in many features. These include their developmental pathways, tissue distribution, phenotype and functions. NK cells and ILC1 contribute to organ homeostasis through the production of key cytokines and chemokines and the elimination of potential harmful bacteria and viruses. In addition, they are equipped with a wide range of receptors, allowing them to detect “stressed cells’ such as cancer cells. Our understanding of the role of innate lymphoid cells in hepatocellular carcinoma (HCC) is growing owing to the development of mouse models, the progress in immunotherapeutic treatment and the recent use of scRNA sequencing analyses. In this review, we summarize the current understanding of NK cells and ILC1 in hepatocellular carcinoma and discuss future strategies to take advantage of these innate immune cells in anti-tumor immunity. Immunotherapies hold great promise in HCC, and a better understanding of the role and function of NK cells and ILC1 in liver cancer could pave the way for new NK cell and/or ILC1-targeted treatment.

Natural Killer-Dendritic Cell Interactions in Liver Cancer: Implications for Immunotherapy

Simple Summary

The reciprocal crosstalk between dendritic cells (DCs) and natural killer (NK) cells plays a pivotal role in regulating immune defense against viruses and tumors. The Th-cell polarizing ability, cytokine-producing capacity, chemokine expression, and migration of DCs are regulated by activated NK cells. Conversely, the effector functions including lysis and cytokine production, proliferation, and migration of NK cells are influenced by close interactions with activated DCs. In this review, we explore the impact of DC–NK cell crosstalk and its therapeutic potential in immune control of liver malignances.

Abstract

Natural killer (NK) and dendritic cells (DCs) are innate immune cells that play a crucial role in anti-tumor immunity. NK cells kill tumor cells through direct cytotoxicity and cytokine secretion. DCs are needed for the activation of adaptive immune responses against tumor cells. Both NK cells and DCs are subdivided in several subsets endowed with specialized effector functions. Crosstalk between NK cells and DCs leads to the reciprocal control of their activation and polarization of immune responses. In this review, we describe the role of NK cells and DCs in liver cancer, focusing on the mechanisms involved in their reciprocal control and activation. In this context, intrahepatic NK cells and DCs present unique immunological features, due to the constant exposure to non-self-circulating antigens. These interactions might play a fundamental role in the pathology of primary liver cancer, namely hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC). Additionally, the implications of these immune changes are relevant from the perspective of improving the cancer immunotherapy strategies in HCC and ICC patients.

Innate lymphocytes: pathogenesis and therapeutic targets of liver diseases and cancer

The liver is a lymphoid organ with unique immunological properties, particularly, its predominant innate immune system. The balance between immune tolerance and immune activity is critical to liver physiological functions and is responsible for the sensitivity of this organ to numerous diseases, including hepatotropic virus infection, alcoholic liver disease, nonalcoholic fatty liver disease, autoimmune liver disease, and liver cancer, which are major health problems globally. In the past decade, with the discovery of liver-resident natural killer cells, the importance of innate lymphocytes with tissue residency has gradually become the focus of research. In this review, we address the current knowledge regarding hepatic innate lymphocytes with unique characteristics, including NK cells, ILC1/2/3s, NKT cells, γδ T cells, and MAIT cells, and their potential roles in liver homeostasis maintenance and the progression of liver diseases and cancer. A better understanding of the immunopathogenesis of hepatic innate lymphocytes will be helpful for proposing effective treatments for liver diseases and cancer.

Tumor microenvironment in primary liver tumors: A challenging role of natural killer cells

In the last years, several studies have been focused on elucidate the role of tumor microenvironment (TME) in cancer development and progression. Within TME, cells from adaptive and innate immune system are one of the main abundant components. The dynamic interactions between immune and cancer cells lead to the activation of complex molecular mechanisms that sustain tumor growth. This important cross-talk has been elucidate for several kind of tumors and occurs also in patients with liver cancer, such as hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (iCCA). Liver is well-known to be an important immunological organ with unique microenvironment. Here, in normal conditions, the rich immune-infiltrating cells cooperate with non-parenchymal cells, such as liver sinusoidal endothelial cells and Kupffer cells, favoring self-tolerance against gut antigens. The presence of underling liver immunosuppressive microenvironment highlights the importance to dissect the interaction between HCC and iCCA cells with immune infiltrating cells, in order to understand how this cross-talk promotes tumor growth. Deeper attention is, in fact, focused on immune-based therapy for these tumors, as promising approach to counteract the intrinsic anti-tumor activity of this microenvironment. In this review, we will examine the key pathways underlying TME cell-cell communications, with deeper focus on the role of natural killer cells in primary liver tumors, such as HCC and iCCA, as new opportunities for immune-based therapeutic strategies.

The interplay between innate lymphoid cells and T cells

ILCs and T cells are closely related functionally but they significantly differ in their ability to circulate, expand, and renew. Cooperation and reciprocal functional regulation suggest that these cell types are more complementary than simply redundant during immune responses. How ILCs shape T-cell responses is strongly dependent on the tissue and inflammatory context. Likewise, indirect regulation of ILCs by adaptive immunity is induced by environmental cues such as the gut microbiota. Here, we review shared requirements for the development and function of both cell types and divergences in the orchestration of prototypic immune functions. We discuss the diversity of functional interactions between T cells and ILCs during homeostasis and immune responses. Identifying the location and the nature of the tissue microenvironment in which these interactions are taking place may uncover the remaining mysteries of their close encounters.

Recent Advances: The Imbalance of Immune Cells and Cytokines in the Pathogenesis of Hepatocellular Carcinoma

Recent advancement in the immunological understanding of genesis of hepatocellular carcinoma (HCC) has implicated a decline in anti-tumour immunity on the background of chronic inflammatory state of liver parenchyma. The development of HCC involves a network of immunological activity in the tumour microenvironment involving continuous interaction between tumour and stromal cells. The reduction in anti-tumour immunity is secondary to changes in various immune cells and cytokines, and the tumour microenvironment plays a critical role in modulating the process of liver fibrosis, hepatocarcinogenesis, epithelial-mesenchymal transition (EMT), tumor invasion and metastasis. Thus, it is considered as one of primary factor behind the despicable tumour behavior and observed poor survival; along with increased risk of recurrence following treatment in HCC. The primary intent of the present review is to facilitate the understanding of the complex network of immunological interactions of various immune cells, cytokines and tumour cells associated with the development and progression of HCC.

CD49a+CD49b+ NK cells induced by viral infection reflect an activated state of conventional NK cells

Natural killer (NK) cells are important innate effectors that play a pivotal role in the defense against tumors and infections and participate in regulating adaptive immunity. Recent studies have revealed phenotypic and functional heterogeneity of NK cells. Here, using murine models of acute and chronic lymphocytic choriomeningitis virus infection, we observed that a CD49a⁺ CD49b⁺ NK cell subset emerged in the liver and other tissues, and underwent vigorous expansion following viral infection, before progressively decreasing in cell number. These viral infection-induced CD49a⁺CD49b⁺ NK cells displayed an activated and mature phenotype. Moreover, compared with liver-resident NK cells and conventional NK (cNK) cells, CD49a⁺CD49b⁺ NK cells showed increased functional competence, as evidenced by higher amounts of IFN-γ production and stronger cytotoxic capabilities during viral infection. Generation of these CD49a⁺CD49b⁺ NK cells was shown to be independent of the T-bet transcription factor. Adoptive transfer experiments revealed that cNK cells could convert into CD49a⁺CD49b⁺ NK cells following viral infection. Collectively, these results suggest that viral infection-induced CD49a⁺CD49b⁺ NK cells represent a transiently activated state of cNK cells.

Transcriptional Regulation of Mouse Tissue-Resident Natural Killer Cell Development

Natural killer (NK) cells are cytotoxic innate lymphocytes that are well-known for their ability to kill infected or malignant cells. Beyond their roles in tumor surveillance and anti-pathogen defense, more recent studies have highlighted key roles for NK cells in a broad range of biological processes, including metabolic homeostasis, immunomodulation of T cells, contact hypersensitivity, and pregnancy. Consistent with the breadth and diversity of these functions, it is now appreciated that NK cells are a heterogeneous population, comprised of specialized and sometimes tissue-specific subsets with distinct phenotypes and effector functions. Indeed, in addition to the conventional NK cells (cNKs) that are abundant and have been well-studied in the blood and spleen, distinct subsets of tissue-resident NK cells (trNKs) and "helper" Group 1 innate lymphoid cells (ILC1s) have now been described in multiple organs and tissues, including the liver, uterus, thymus, adipose tissue, and skin, among others. The cNK, trNK, and/or helper ILC1 populations that co-exist in these various tissues exhibit both common and distinct developmental requirements, suggesting that a combination of lineage-, subset-, and tissue-specific differentiation processes may contribute to the unique functional properties of these various populations. Here, we provide an overview of the transcriptional regulatory pathways known to instruct the development and differentiation of cNK, trNK, and helper ILC1 populations in specific tissues in mice.

Mass Cytometry Studies of Patients With Autoimmune Endocrine Diseases Reveal Distinct Disease-Specific Alterations in Immune Cell Subsets

Although there is evidence that autoimmune diseases share similar immunogenetic mechanisms, studies comparing peripheral CD45⁺ cells from patients with autoimmune endocrine diseases in parallel are limited. In this study, we applied high-dimensional single-cell mass cytometry to phenotypically characterize PBMC from patients with new-onset (N-T1D) and long-standing type 1 diabetes, Hashimoto's thyroiditis (HT), Graves' disease and autoimmune Addison's disease (AD), as well as healthy controls. The frequency of CD20^loCD27^hiCD38^hiHLA-DR^int plasmablasts, CD86⁺CD14^loCD16⁺ non-classical monocytes and two subsets of CD56^dimHLA-DR⁺IFN-γ⁺ NK cells were increased in patients with HT. Subsets of CD56^dimCD69⁺HLA-DR^- NK cells and CD8⁺ TEMRA cells, both expressing IFN-γ, were expanded and reduced, respectively, in the N-T1D group. In addition, patients with AD were characterized by an increased percentage of central memory CD8⁺ T cells that expressed CCR4, GATA3, and IL-2. We demonstrate that patients with N-T1D, HT, and AD had altered frequencies of distinct subsets within antigen-presenting and cytotoxic cell lineages. Previously unreported alterations of specific cell subsets were identified in samples from patients with HT and AD. Our study might contribute to a better understanding of shared and diverging immunological features between autoimmune endocrine diseases.

Tumor Microenvironment-Associated Extracellular Matrix Components Regulate NK Cell Function

The tumor microenvironment (TME) is composed of multiple infiltrating host cells (e.g., endothelial cells, fibroblasts, lymphocytes, and myeloid cells), extracellular matrix, and various secreted or cell membrane-presented molecules. Group 1 innate lymphoid cells (ILCs), which includes natural killer (NK) cells and ILC1, contribute to protecting the host against cancer and infection. Both subsets are able to quickly produce cytokines such as interferon gamma (IFN-γ), chemokines, and other growth factors in response to activating signals. However, the TME provides many molecules that can prevent the potential effector function of these cells, thereby protecting the tumor. For example, TME-derived tumor growth factor (TGF)-β and associated members of the superfamily downregulate NK cell cytotoxicity, cytokine secretion, metabolism, proliferation, and induce effector NK cells to upregulate ILC1-like characteristics. In concert, a family of carbohydrate-binding proteins called galectins, which can be produced by different cells composing the TME, can downregulate NK cell function. Matrix metalloproteinase (MMP) and a disintegrin and metalloproteinase (ADAM) are also enzymes that can remodel the extracellular matrix and shred receptors from the tumor cell surface, impairing the activation of NK cells and leading to less effective effector functions. Gaining a better understanding of the characteristics of the TME and its associated factors, such as infiltrating cells and extracellular matrix, could lead to tailoring of new personalized immunotherapy approaches. This review provides an overview of our current knowledge on the impact of the TME and extracellular matrix-associated components on differentiation, impairment, and function of NK cells.

The Transcription Factor Promyelocytic Leukemia Zinc Finger Protein Is Associated With Expression of Liver-Homing Receptors on Human Blood CD56bright Natural Killer Cells

The transcription factor promyelocytic leukemia zinc finger protein (PLZF) is involved in the development of natural killer (NK) cells and innate lymphoid cells, including liver-resident NK cells in mice. In human NK cells, the role of PLZF in liver residency is still unknown. Expression of PLZF in matched human peripheral blood- and liver-derived NK cells and the association of PLZF expression with surface molecules and transcription factors relevant for tissue residency were investigated using multiparameter flow cytometry and assessing single-cell messenger RNA (mRNA) levels. Intrahepatic cluster of differentiation (CD)56^bright NK cells expressed significantly higher levels of PLZF than peripheral blood CD56^bright NK cells, which were predominantly PLZF^lo. Expression of PLZF was highest within C-X-C motif chemokine receptor 6 (CXCR6)⁺CD69⁺ liver-resident NK cells among intrahepatic CD56^bright NK cell populations. Association of PLZF with liver-residency markers was also reflected at mRNA levels. A small PLZF^hiCD56^bright NK cell population was identified in peripheral blood that also expressed the liver-residency markers CXCR6 and CD69 and shared functional characteristics with liver-resident NK cells. Conclusion: PLZF is implicated as part of a transcriptional network that promotes liver residency of human NK cells. Expression of liver-homing markers on peripheral blood PLZF^hiCD56^bright NK cells identifies an intermediate population potentially contributing to the maintenance of liver-resident NK cells.

NK cells induce hepatic ER stress to promote insulin resistance in obesity through osteopontin production

High-fat diet (HFD) induced hepatic endoplasmic reticulum (ER) stress drives insulin resistance (IR) and steatosis. NK cells in adipose tissue play an important role in the pathogenesis of IR in obesity. Whether NK cells in the liver can induce hepatic ER stress and thus promote IR in obesity is still unknown. We demonstrate that HFD-fed mice display elevated production of proinflammatory cytokine osteopontin (OPN) in hepatic NK cells, especially in CD49a⁺ DX5^- tissue-resident NK (trNK) cells. Obesity-induced ER stress, IR, and steatosis in the liver are ameliorated by ablating NK cells with neutralizing antibody in HFD-fed mice. OPN treatment enhances the expression of ER stress markers, including p-PERK, p-eIF2, ATF4, and CHOP in both murine liver tissues and HL-7702, a human liver cell line. Pretreatment of HL-7702 cells with OPN promotes hyperactivation of JNK and subsequent decrease of tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1), resulting in impaired insulin signaling, which can be reversed by inhibiting ER stress. Collectively, we demonstrate that hepatic NK cells induce obesity-induced hepatic ER stress, and IR through OPN production.

Tissue-resident NK cells and other innate lymphoid cells

Natural killer (NK) cells are important innate effectors for their defense against pathogens and tumors without the need of prior sensitization. Along with the growing understanding of basic NK cell biology, it has been widely accepted that NK cells are a heterogeneous population of innate lymphoid cell (ILC) family. Apart from the conventional NK cell (cNK) subset that circulates throughout the body, some non-lymphoid tissues contain tissue-resident NK (trNK) cell subsets, and the composition of NK cell subsets varies greatly with different locations. Except for cNK cells, other ILCs are known as tissue-resident cells. In this review, we summarize the unique properties of trNK cells, discuss their lineage relationship with other ILCs, and highlight recent advances in our understanding of the functions of trNK cells and other ILCs.

Context Dependent Role of Type 2 Innate Lymphoid Cells in Allergic Skin Inflammation

The discovery of innate lymphoid cells (ILC) has profoundly influenced the understanding of innate and adaptive immune crosstalk in health and disease. ILC and T cells share developmental and functional characteristics such as the lineage-specifying transcription factors and effector cytokines, but importantly ILC do not display rearranged antigen-specific receptors. Similar to T cells ILC are subdivided into 3 different helper-like subtypes, namely ILC1-3, and a killer-like subtype comprising natural killer (NK) cells. Increasing evidence supports the physiological relevance of ILC, e.g., in wound healing and defense against parasites, as well as their pathogenic role in allergy, inflammatory bowel diseases or psoriasis. Group 2 ILC have been attributed to the pathogenesis of allergic diseases like asthma and atopic dermatitis. Other inflammatory skin diseases such as allergic contact dermatitis are profoundly shaped by inflammatory NK cells. This article reviews the role of ILC in allergic skin diseases with a major focus on ILC2. While group 2 ILC are suggested to contribute to the pathogenesis of type 2 dominated inflammation as seen in atopic dermatitis, we have shown that lack of ILC2 in type 1 dominated contact hypersensitivity results in enhanced inflammation, suggesting a regulatory role of ILC2 in this context. We provide a concept of how ILC2 may influence context dependent the mutual counterbalance between type I and type II immune responses in allergic skin diseases.

Maturation of the Human Intestinal Immune System Occurs Early in Fetal Development

There are limited data on fetal and early life development of human intestinal immunity. Using mass cytometry (CyTOF) and next-generation sequencing of B and T cell receptor (BCR and TCR) repertoires, we demonstrate complex intestinal immunity from 16 weeks' gestational age (GA). Both BCR and TCR repertoires are diverse with CDRH and CDR3β length increasing with advancing GA. The difference-from-germline, CDR insertions and/or deletions, similarly occur in utero for TCR but not BCR, suggesting earlier mucosal T than B cell maturity. Innate immunity is dominated by macrophages, dendritic cells (DCs), innate lymphoid cells (ILCs), and natural killer (NK) cells. Follicular and transitional B cells are enriched in fetuses while CD69⁺IgM⁺ B cells are abundant in infants. Both CD4⁺ and CD8⁺ T cells are abundant, capable of secreting cytokines and are phenotypically of the tissue resident memory state in utero. Our data provide the foundation for a 2nd trimester and infant intestinal immune atlas and suggest that a complex innate and adaptive immune landscape exists significantly earlier than previously reported.

CD8+ T Cells Promote Maturation of Liver-Resident NK Cells Through the CD70-CD27 axis

Liver-resident natural killer (LrNK) cells are a unique subset of NK cells that are distinct from conventional NK cells. However, little is known about the mechanisms by which LrNK cells mature. In this study, we discovered that LrNK cells exhibit a relatively immature phenotype and impaired cytotoxic capacity in the absence of CD8⁺ T cells. The provision of CD8⁺ T cells to Cd8^-/- or Rag1^-/- mice led to the restoration of LrNK cell maturation. Furthermore, co-culture with CD8⁺ T cells induced immature CD27⁺ LrNK cells to convert into mature CD27^- LrNK cells, whereas blocking the interaction of CD70 and CD27 abrogated the ability of CD8⁺ T cells to promote the maturation of LrNK cells. Conclusion: Our findings indicate that CD8⁺ T cells promote the maturation of LrNK cells through the CD70-CD27 axis, and therefore highlight a previously unknown mechanism responsible for the mediation of LrNK cell maturation.

A novel spleen-resident immature NK cell subset and its maturation in a T-bet-dependent manner

NK cells are thought to develop primarily in the bone marrow during adult life. However, increasing evidence shows that NK cell developmental intermediates can be found in different peripheral tissues with unique characteristics. Here, we identified a unique NK cell subset with the CD49a^-CD49b^- phenotype in the spleen. These cells displayed an immature phenotype and weak abilities in cytotoxicity and cytokine production. Adoptive transfer experiments revealed that they could develop into mature conventional NK (cNK) cells. Transcriptome analysis further confirmed their immature features. Parabiosis experiments revealed that these cells maintained tissue-resident properties in the spleen. Moreover, T-bet deficiency intrinsically impaired the ability of these cells to develop into mature cNK cells. Thus, our study identified a spleen-resident immature NK cell subset that could undergo extramedullary maturation in a T-bet dependent manner.

The Roles of Liver-Resident Lymphocytes in Liver Diseases

Tissue-resident lymphocytes usually reside in barrier sites and are involved in innate and adaptive immunity. In recent years, many studies have shown that multiple types of lymphocytes are resident in the liver, including memory CD8⁺ T (T_RM) cells; "unconventional" T cells, such as invariant natural killer T (iNKT) cells, mucosal associated invariant T (MAIT) cells, and γδT cells; innate lymphoid cells (ILCs) such as natural killer (NK) cells and other ILCs. Although diverse types of tissue-resident lymphocytes share similar phenotypes, functional properties, and transcriptional regulation, the unique microenvironment of the liver can reshape their phenotypic and functional characteristics. Liver-resident lymphocytes serve as sentinels and perform immunosurveillance in response to infection and non-infectious insults, and are involved in the maintenance of liver homeostasis. Under the pathological conditions, distinct liver-resident lymphocytes exert protective or pathological effects in the process of various liver diseases. In this review, we highlight the unique properties of liver-resident lymphocytes, and discuss their functional characteristics in different liver diseases.

Accumulation of Tumor-Infiltrating CD49a+ NK Cells Correlates with Poor Prognosis for Human Hepatocellular Carcinoma

The discovery of CD49a⁺ liver-resident natural killer (NK) cells in mice alters our view of NK cells and provides another opportunity to study NK cells. Although evidence has suggested roles for NK cells in liver diseases, whether and how CD49a⁺ NK cells contribute to liver diseases remain unclear. In this study, we observed that accumulation of CD49a⁺ tissue-resident NK cells in human hepatocellular carcinoma (HCC) was higher than in peritumoral tissues. We studied the exhausted and regulatory phenotypes of CD49a⁺ tissue-resident NK cells by analysis of protein and mRNA. The proportion of CD49a⁺ NK cells was positively correlated to the proportion of NK cells expressing inhibitory receptors. In addition, CD49a⁺ NK cells expressed more of checkpoint molecules PD-1, CD96, and TIGIT. Transcriptomic analysis implicated CD49a⁺ tissue-resident NK cells in the negative regulation of immune responses. Comparison of murine and human CD49a⁺ NK cells revealed their distinct characteristics and functions. Finally, accumulation of tissue-resident CD49a⁺ NK cells in liver tumor was correlated to deteriorating disease condition and poor prognosis. Our findings show that CD49a⁺ NK cells accumulate in liver tumor and suggest a role for CD49a⁺ NK cells in the negative regulation of immune responses and the development of HCC.

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.

Natural Killer Cells and Type 1 Innate Lymphoid Cells Are New Actors in Non-alcoholic Fatty Liver Disease

Obesity and associated liver diseases (Non Alcoholic Fatty Liver Disease, NAFLD) are a major public health problem with increasing incidence in Western countries (25% of the affected population). These complications develop from a fatty liver (steatosis) to an inflammatory state (steatohepatitis) evolving toward fibrosis and hepatocellular carcinoma. Lipid accumulation in the liver contributes to hepatocyte cell death and promotes liver injury. Local immune cells are activated either by Danger Associated Molecular Patterns (DAMPS) released by dead hepatocytes or by bacterial products (PAMPS) reaching the liver due to increased intestinal permeability. The resulting low-grade inflammatory state promotes the progression of liver complications toward more severe grades. Innate lymphoid cells (ILC) are an heterogeneous family of five subsets including circulating Natural Killer (NK) cells, ILC1, ILC2, ILC3, and lymphocytes tissue-inducer cells (LTi). NK cells and tissue-resident ILCs, mainly located at epithelial surfaces, are prompt to rapidly react to environmental changes to mount appropriate immune responses. Recent works have demonstrated the interplay between ILCs subsets and the environment within metabolic active organs such as liver, adipose tissue and gut during diet-induced obesity leading or not to hepatic abnormalities. Here, we provide an overview of the newly roles of NK cells and ILC1 in metabolism focusing on their contribution to the development of NAFLD. We also discuss recent studies that demonstrate the ability of these two subsets to influence tissue-specific metabolism and how their function and homeostasis are affected during metabolic disorders.

Hepatic Natural Killer Cells: Organ-Specific Sentinels of Liver Immune Homeostasis and Physiopathology

The liver is considered a preferential tissue for NK cells residency. In humans, almost 50% of all intrahepatic lymphocytes are NK cells that are strongly imprinted in a liver-specific manner and show a broad spectrum of cellular heterogeneity. Hepatic NK (he-NK) cells play key roles in tuning liver immune response in both physiological and pathological conditions. Therefore, there is a pressing need to comprehensively characterize human he-NK cells to better understand the related mechanisms regulating their effector-functions within the dynamic balance between immune-tolerance and immune-surveillance. This is of particular relevance in the liver that is the only solid organ whose parenchyma is constantly challenged on daily basis by millions of foreign antigens drained from the gut. Therefore, the present review summarizes our current knowledge on he-NK cells in the light of the latest discoveries in the field of NK cell biology and clinical relevance.

γδT Cells Suppress Liver Fibrosis via Strong Cytolysis and Enhanced NK Cell-Mediated Cytotoxicity Against Hepatic Stellate Cells

Liver fibrosis is the excessive accumulation of extracellular matrix proteins, resulting from maladaptive wound healing responses to chronic liver injury. γδT cells are important in chronic liver injury pathogenesis and subsequent liver fibrosis; however, their role and underlying mechanisms are not fully understood. The present study aims to assess whether γδT cells contribute to liver fibrosis regression. Using a carbon tetrachloride (CCl₄)-induced murine model of liver fibrosis in wild-type (WT) and γδT cell deficient (TCRδ^−/−) mice, we demonstrated that γδT cells protected against liver fibrosis and exhibited strong cytotoxicity against activated hepatic stellate cells (HSCs). Further study show that chronic liver inflammation promoted hepatic γδT cells to express NKp46, which contribute to the direct killing of activated HSCs by γδT cells. Moreover, we identified that an IFNγ-producing γδT cell subset (γδT1) cells exhibited stronger cytotoxicity against activated HSCs than the IL-17-producing subset (γδT17) cells upon chronic liver injury. In addition, γδT cells promoted the anti-fibrotic ability of conventional natural killer (cNK) cells and liver-resident NK (lrNK) cells by enhancing their cytotoxicity against activated HSCs. The cell crosstalk between γδT and NK cells was shown to depend partly on co-stimulatory receptor 4-1BB (CD137) engagement. In conclusion, our data confirmed the protective effects of γδT cells, especially the γδT1 subset, by directly killing activated HSCs and increasing NK cell-mediated cytotoxicity against activated HSCs in CCl₄-induced liver fibrosis, which suggest valuable therapeutic targets to treat liver fibrosis.

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.

Generation of a common innate lymphoid cell progenitor requires interferon regulatory factor 2

Innate lymphoid cells (ILCs), composed of heterogeneous populations of lymphoid cells, contribute critically to immune surveillance at mucosal surfaces. ILC subsets develop from common lymphoid progenitors through stepwise lineage specification. However, the composition and temporal regulation of the transcription factor network governing such a process remain incompletely understood. Here, we report that deletion of the transcription factor interferon regulatory factor 2 (IRF-2), known also for its importance in the maturation of conventional NK cells, resulted in an impaired generation of ILC1, ILC2 and ILC3 subsets with lymphoid tissue inducer (LTi)-like cells hardly affected. In IRF-2-deficient mice, PD-1hi ILC precursors (ILCPs) that generate these three ILCs but not LTi-like cells were present at normal frequency, while their sub-population expressing high amounts of PLZF, another marker for ILCPs, was severely reduced. Notably, these IRF-2-deficient ILCPs contained normal quantities of PLZF-encoding Zbtb16 messages, and PLZF expression in developing invariant NKT cells within the thymus was unaffected in these mutant mice. These results point to a unique, cell-type selective role for IRF-2 in ILC development, acting at a discrete step critical for the generation of functionally competent ILCPs.

Multiple receptors converge on H2-Q10 to regulate NK and γδT-cell development

Class Ib major histocompatibility complex (MHC) is an extended family of molecules, which demonstrate tissue-specific expression and presentation of monomorphic antigens. These characteristics tend to imbue class Ib MHC with unique functions. H2-Q10 is potentially one such molecule that is overexpressed in the liver but its immunological function is not known. We have previously shown that H2-Q10 is a ligand for the natural killer cell receptor Ly49C and now, using H2-Q10-deficient mice, we demonstrate that H2-Q10 can also stabilize the expression of Qa-1b. In the absence of H2-Q10, the development and maturation of conventional hepatic natural killer cells is disrupted. We also provide evidence that H2-Q10 is a new high affinity ligand for CD8αα and controls the development of liver-resident CD8αα γδT cells. These data demonstrate that H2-Q10 has multiple roles in the development of immune subsets and identify an overlap of recognition within the class Ib MHC that is likely to be relevant to the regulation of immunity.

Tissue-resident lymphocytes: from adaptive to innate immunity

Efficient immune responses against invading pathogens often involve coordination between cells from both the innate and adaptive immune systems. For multiple decades, it has been believed that CD8⁺ memory T cells and natural killer (NK) cells constantly and uniformly recirculate. Only recently was the existence of noncirculating memory T and NK cells that remain resident in the peripheral tissues, termed tissue-resident memory T (T_RM) cells and tissue-resident NK (trNK) cells, observed in various organs owing to improved techniques. T_RM cells populate a wide range of peripheral organs, including the skin, sensory ganglia, gut, lungs, brain, salivary glands, female reproductive tract, and others. Recent findings have demonstrated the existence of T_RM in the secondary lymphoid organs (SLOs) as well, leading to revision of the classic theory that they exist only in peripheral organs. trNK cells have been identified in the uterus, skin, kidney, adipose tissue, and salivary glands. These tissue-resident lymphocytes do not recirculate in the blood or lymphatic system and often adopt a unique phenotype that is distinct from those of circulating immune cells. In this review, we will discuss the recent findings on the tissue residency of both innate and adaptive lymphocytes, with a particular focus on CD8⁺ memory T cells, and describe some advances regarding unconventional T cells (invariant NKT cells, mucosal-associated invariant T cells (MAIT), and γδ T cells) and the emerging family of trNK cells. Specifically, we will focus on the phenotypes and functions of these subsets and discuss their implications in anti-viral and anti-tumor immunity.

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.

Cytokine-Based Generation of CD49a+Eomes-/+ Natural Killer Cell Subsets

Recent studies have identified CD49a⁺Eomes⁻ and CD49a⁺Eomes⁺ subsets of tissue-resident NK (trNK) cells in different organs of the mouse. However, the characteristics of CD49a⁺Eomes^−/+ NK cell development and the regulation of Eomes expression in NK cells remain unclear. Here, we established an in vitro cytokine-based feeder-free system in which bone marrow progenitor cells differentiate into CD49a⁺ NK cells. IL-15 was identified as being the key cytokine in this system that supported the development and maintenance of CD49a⁺ NK cells. The CD49a⁺ NK cells generated were Eomes⁻CD49b⁻ and shared the same phenotype as hepatic trNK cells. IL-4 induced the expression of Eomes in generated NK cells and converted them into CD49a⁺Eomes⁺ cells, which were phenotypically and functionally similar to uterine trNK cells. Moreover, the IL-4/STAT6 axis was identified as being important in the generation of CD49a⁺Eomes⁺ induced NK cells. Collectively, these studies describe an approach to generate CD49a⁺Eomes^−/+ subsets of NK cells and demonstrate important roles for IL-15 and IL-4 in the differentiation of these cells. These findings have potential for developmental research underlying the generation of different subsets of NK cells and the application of adoptive NK cell transfer therapies.

Runx3 Mediates Resistance to Intracellular Bacterial Infection by Promoting IL12 Signaling in Group 1 ILC and NCR+ILC3

Innate lymphoid cells (ILCs) are the most recently identified family of the innate immune system and are hypothesized to modulate immune functions prior to the generation of adaptive immune responses. Subsets of ILCs reside in the mucosa and regulate immune responses to external pathogens; however, their role and the mechanism by which they protect against intracellular bacterial infection is not completely understood. In this report, using S. typhimurium and L. monocytogenes, we found that the levels of group 1 ILCs and NCR⁺ ILC3s were increased upon infection and that these increases were associated with Runt-related transcription factor 3 (Runx3) expression. Runx3 ^fl/fl PLZF-cre mice were much more sensitive to infection with the intracellular bacterial pathogens S. typhimurium and L. monocytogenes partially due to abnormal Group 1 ILC and NCR⁺ILC3 function. We also found that Runx3 directly binds to the Il12Rβ2 promoter and intron 8 to accelerate the expression of Il12Rβ2 and modulates IFNγ secretion triggered by the IL12/ STAT4 axis. Therefore, we demonstrate that Runx3 influences group 1 ILC- and NCR+ILC3-mediated immune protection against intracellular bacterial infections of both the gut and liver.

Natural Killer Cells in Liver Disease and Hepatocellular Carcinoma and the NK Cell-Based Immunotherapy

Nature killer (NK) cells play a critical role in host innate and adaptive immune defense against viral infections and tumors. NK cells are enriched in liver hematopoietic cells with unique NK repertories and functions to safeguard liver cells against hepatitis virus infection or malignancy transformation. However, accumulating evidences were found that the NK cells were modulated by liver diseases and liver cancers including hepatocellular carcinoma (HCC) and showed impaired functions failing to activate the elimination of the viral-infected cells or tumor cells and were further involved in the pathogenesis of liver injury and inflammation. The full characterization of circulation and intrahepatic NK cell phenotype and function in liver disease and liver cancer has not only provided new insight into the disease pathogenesis but has also discovered new targets for developing new NK cell-based therapeutic strategies. This review will discuss and summarize the NK cell phenotypic and functional changes in liver disease and HCC, and the NK cell-based immunotherapy approaches and progresses for cancers including HCC will also be reviewed.

Lack of Type 2 Innate Lymphoid Cells Promotes a Type I-Driven Enhanced Immune Response in Contact Hypersensitivity

Allergic contact dermatitis and its animal model, contact hypersensitivity, are T-cell-mediated inflammatory skin diseases that require activation of the innate immune system. Here we investigate the role of innate lymphoid cells (ILCs) during the elicitation phase of 2,4,6-trinitrochlorobenzene-induced contact hypersensitivity using EomesGfp/+ x Rorc(γt)-CreTg x Rosa26RYfp/+ reporter mice. Ear swelling responses, cutaneous ILC numbers, and cytokine production were determined at different time points. Functional analyses were performed in a CD90.1/.2 congenic adoptive transfer model that allowed selective antibody-mediated depletion of ILCs before hapten challenge, and in Rorasg/floxIl7rCre/+ mice, which lack ILC2. Hapten challenge induced early increases of natural killer cells in skin and ear draining lymph nodes corresponding to the peak ear swelling response. In contrast, ILC1, 2, and 3 showed a delayed increase in numbers corresponding to the contact hypersensitivity resolution phase. Hapten challenge induced increased marker cytokines in all ILC subtypes and an activated phenotype in ILC2. Depletion of all ILC resulted in a significantly enhanced ear swelling response. Similarly, ILC2-deficient mice (Rorasg/floxIl7rCre/+) displayed increased ear swelling responses on hapten challenge, suggesting that ILC2 act as negative regulators in the type 1-dominated immune response of contact hypersensitivity.

Hepatic irradiation persistently eliminates liver resident NK cells

Hepatic irradiation for the treatment of hepatobiliary malignancies often indirectly damages liver tissue and promotes the development of liver fibrosis. However, little is known concerning the effects of hepatic irradiation on the liver immune system, including natural killer (NK) cells. The aim of this study was therefore to investigate how hepatic irradiation influences the functions and characteristics of liver resident NK cells. An established murine hepatic irradiation model was used to examine the specific effects of hepatic irradiation on immune cell populations and metastasis. This analysis demonstrated that hepatic irradiation decreased the number of liver resident NK cells (DX5^–TRAIL⁺), but did not affect the total NK number or proportions of NK cells in the liver or spleen. This effect was correlated with the hepatic irradiation dose. Surprisingly, the liver resident NK population had not recovered by two months after hepatic irradiation. We also found that hepatic irradiation limited the cytotoxic effects of liver-derived lymphocytes against a mouse hepatoma cell line and promoted hepatic metastases in an in vivo model, although adoptive transfer of activated NK cells could alleviate metastatic growth. Finally, we demonstrated that hepatic irradiation disrupted the development of liver-resident NK cells, even after the adoptive transfer of precursor cells from the bone marrow, liver, and spleen, suggesting that irradiation had altered the developmental environment of the liver. In summary, our data demonstrated that hepatic irradiation abolished the DX5^–TRAIL⁺ liver-resident NK cell population and dampened antitumor activities in the liver for at least two months. Additionally, hepatic irradiation prevented differentiation of precursor cells into liver-resident NK cells.

Gene expression of the liver of vaccination-protected mice in response to early patent infections of Plasmodium chabaudi blood-stage malaria

BACKGROUND

The role of the liver for survival of blood-stage malaria is only poorly understood. In experimental blood-stage malaria with Plasmodium chabaudi, protective vaccination induces healing and, thus, survival of otherwise lethal infections. This model is appropriate to study the role of the liver in vaccination-induced survival of blood-stage malaria.

METHODS

Female Balb/c mice were vaccinated with a non-infectious vaccine consisting of plasma membranes isolated in the form of erythrocyte ghosts from P. chabaudi-infected erythrocytes at week 3 and week 1 before infection with P. chabaudi blood-stage malaria. Gene expression microarrays and quantitative real-time PCR were used to investigate the response of the liver, in terms of expression of mRNA and long intergenic non-coding (linc)RNA, to vaccination-induced healing infections and lethal P. chabaudi malaria at early patency on day 4 post infection, when parasitized erythrocytes begin to appear in peripheral blood.

RESULTS

In vaccination-induced healing infections, 23 genes were identified to be induced in the liver by > tenfold at p < 0.01. More than one-third were genes known to be involved in erythropoiesis, such as Kel, Rhag, Ahsp, Ermap, Slc4a1, Cldn13 Gata1, and Gfi1b. Another group of > tenfold expressed genes include genes involved in natural cytotoxicity, such as those encoding killer cell lectin-like receptors Klrb1a, Klrc3, Klrd1, the natural cytotoxicity-triggering receptor 1 Ncr1, as well as the granzyme B encoding Gzmb. Additionally, a series of genes involved in the control of cell cycle and mitosis were identified: Ccnb1, Cdc25c, Ckap2l were expressed > tenfold only in vaccination-protected mice, and the expression of 22 genes was at least 100% higher in vaccination-protected mice than in non-vaccinated mice. Furthermore, distinct lincRNA species were changed by > threefold in livers of vaccination-protected mice, whereas lethal malaria induced different lincRNAs.

CONCLUSION

The present data suggest that protective vaccination accelerates the malaria-induced occurrence of extramedullary erythropoiesis, generation of liver-resident cytotoxic cells, and regeneration from malaria-induced injury in the liver at early patency, which may be critical for final survival of otherwise lethal blood-stage malaria of P. chabaudi.