Groups Of Innate Lymphoid Cells Research Articles

The Roles of Various Immune Cell Populations in Immune Response against Helminths.

Helminths are multicellular parasites that are a substantial problem for both human and veterinary medicine. According to estimates, 1.5 billion people suffer from their infection, resulting in decreased life quality and burdens for healthcare systems. On the other hand, these infections may alleviate autoimmune diseases and allergy symptoms. The immune system is programmed to combat infections; nevertheless, its effector mechanisms may result in immunopathologies and exacerbate clinical symptoms. This review summarizes the role of the immune response against worms, with an emphasis on the Th2 response, which is a hallmark of helminth infections. We characterize non-immune cells (enteric tuft cells-ETCs) responsible for detecting parasites, as well as the role of hematopoietic-derived cells (macrophages, basophils, eosinophils, neutrophils, innate lymphoid cells group 2-ILC2s, mast cells, T cells, and B cells) in initiating and sustaining the immune response, as well as the functions they play in granulomas. The aim of this paper is to review the existing knowledge regarding the immune response against helminths, to attempt to decipher the interactions between cells engaged in the response, and to indicate the gaps in the current knowledge.

Comparison of innate lymphoid cells from tissue and blood in chronic tonsillitis and tonsillar hypertrophy.

Recurrent tonsillitis and tonsillar hypertrophy are two common diseases in children for which tonsillectomy is the definitive solution. The underlying causes of both diseases are not fully known. The aim of this study was to identify the predominant innate lymphoid cells in both diseases of the palatine tonsils, which are known to play an important role in the immune system. Children who underwent tonsillectomy were divided into two groups as recurrent tonsillitis and tonsillar hypertrophy according to the indication for surgery. The proportions of innate lymphoid cell (ILC) groups and IFN-gamma, IL-10 and IL-17 secreting T lymphocyte cells were determined in tonsil and blood samples obtained during surgery. Local and peripheral immune responses were evaluated. Innate immune responses and acquired immune responses were compared. The results of our study showed that the proportions of the innate lymphoid cell 1 group (ILC1) were similar in tonsil tissue in patients with recurrent tonsillitis and tonsil hypertrophy, with no statistically significant difference. It was observed that the innate lymphoid cell 2 group (ILC2) was the predominant group in tonsil hypertrophy, the innate lymphoid cell 3 group (ILC3) was the predominant innate lymphoid cell group in recurrent tonsillitis, and the proportion of IL-17 secreting T lymphocytes in blood and tonsillar mononuclear cells was higher in recurrent tonsillitis patients than in tonsil hypertrophy patients. With the results obtained, the predominant innate lymphoid cells in the pathogenesis of both diseases were identified and local and peripheral responses were compared. These findings may be a guide for possible medical treatments for both diseases in the future.

The enrichment of Arg1+ILC2s and ILCregs facilitates the progression of endometriosis: A preliminary study.

Innate lymphoid cells (ILCs) are a kind of lymphocytes that reside in the tissue and have an essential function in the immune microenvironment. However, the relationship between endometriosis (EMS) and ILCs is complex and not fully understood. This study examines several groups of ILCs in the peripheral blood (PB), peritoneal fluid (PF) and endometrium of patients with EMS via flow cytometry. The study observed an increase in PB ILCs, particularly ILC2s and ILCregs subsets and Arg1+ILC2s in the EMS patients were highly activated. EMS patients had significantly higher levels of serum interleukin (IL)-10/33/25 compared to controls. We also found an elevation of Arg1+ILC2s in the PF and higher levels of ILC2s and ILCregs in ectopic endometrium compared with eutopic. Importantly, a positive correlation was observed between the enrichment of Arg1+ILC2s and ILCregs in the PB of EMS patients. The findings indicate that the involvement of Arg1+ILC2s and ILCregs fosters potentially endometriosis progression.

Immunological and Molecular Evaluation of IL-5 in Asthma Patients

Asthma cause airway obstruction and are associated with chronic airway inflammation. Interleukin -5 is mainly produced by Th2 cells, innate lymphoid cells group 2 (ILC2), mast cells, natural killer T cells (NKT), and eosinophils themselves. Material and Method: A case-control study and the implementation steps are divided into 3 main parts, include: Patient selection and sampling, examining the intensity of gene expression. Result: The present study show that the expression of IL-5 gene has increased significantly in asthma. Regarding the intensity of IL-5 gene expression in the patient and control groups, a significant difference can be observed between the two groups in terms of gene expression intensity (PValue=0.0001). Conclusion: The results of the present study show that IL-5 gene expression has been significantly changed in asthma. In terms of the intensity of IL-5 gene expression in the patient and control groups, a significant difference is observed between the two groups (P-Value=0.0001), also the experiment and analysis of the obtained ROC curve shows that a significant change in IL-5 in Asthma.

Immunologic Role of Innate Lymphoid Cells against Mycobacterial tuberculosis Infection.

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M. tb), is one of the leading causes of mortality due to respiratory tract infections worldwide. Infection by M. tb involves activation of a type I immune response characteristic of T helper type 1 (Th1) lymphocytes, natural killer (NK) cells, Interleukin-12 (IL-12), and interferon (IFN)-γ, all of which stimulate the activation of macrophages and robust phagocytosis in order to prevent further infectious manifestations and systemic dissemination. Recent discoveries about innate lymphoid cells (ILCs) have provided further insight about how these cells participate within the protective immune response against M. tb infection and help boost the type I immune response. In order to clearly understand the mechanisms of M. tb infection and advance the efficacy of future treatment and prevention, we must first look at the individual functions each type of immune cell plays within this process, specifically ILCs. By review of the recent literature and current evidence, our group aims to summarize the characterization of the three major groups of ILCs, including NK cells, and analyze the role that each group of ILCs play in the infectious process against M. tb in order to provide a more comprehensive understanding of the host immune response. Equally, previous studies have also highlighted the effects of how administration of the Bacille Calmette-Guérin (BCG) vaccine influences the cells and cytokines of the immune response against M. tb. Our group also aims to highlight the effects that BCG vaccine has on ILCs and how these effects provide added protection against M. tb.

Uterine natural killer cells and successful pregnancy: from mouse experiments to human physiology

Uterine natural killer (uNK) cells, a specific type of natural killer (NK) cells, are important cells at the foeto-maternal interface in humans as well as in mice. uNK cells are part of the innate lymphoid cells group 1. Especially in the mouse, but also in the rat, many in vivo studies have been performed to evaluate the role of uNK cells in placental development. These studies have shown that uNK cells are not indispensable to pregnancy, but that they play an important role in optimal decidual angiogenesis in early pregnancy, trophoblast invasion and spiral artery remodelling in the mouse placenta. Based on the mouse studies, various in vitro studies, as well as immunohistological studies of the human placenta from elective abortions, have shown that uNK cells have similar functions in the human placenta. In the present narrative review, the role of the uNK cells in the development of the mouse and rat placenta will be discussed first. Thereafter, studies on the role of human uNK cells in the human placenta will be reviewed and these studies will be discussed in the light of the knowledge on mouse uNK cells.

Therapeutic Potential of Innate Lymphoid Cells for Multiple Myeloma Therapy.

Simple SummaryMultiple myeloma (MM) is the second most common haematological malignancy. Despite huge progress associated with the introduction of new antimyeloma drugs, MM remains an incurable disease. In this review, we discuss the role of the innate lymphoid system, its role in the pathogenesis of the disease, and the mechanisms by which innate lymphoid cells (ILC) can theoretically achieve therapeutic benefit in MM treatment.Innate lymphoid cells (ILCs) are a recently identified family of lymphocyte-like cells lacking a specific antigen receptor. They are part of the innate immune system. They play a key role in tissue homeostasis and also control inflammatory and neoplastic processes. In response to environmental stimuli, ILCs change their phenotype and functions, and influence the activity of other cells in the microenvironment. ILC dysfunction can lead to a wide variety of diseases, including cancer. ILC can be divided into three subgroups: ILC Group 1, comprising NK cells and ILC1; Group 2, including ILC2 alone; and Group 3, containing Lymphoid Tissue inducers (LTi) and ILC3 cells. While Group 1 ILCs mainly exert antitumour activity, Group 2 and Group 3 ILCs are protumorigenic in nature. A growing body of preclinical and clinical data support the role of ILCs in the pathogenesis of multiple myeloma (MM). Therefore, targeting ILCs may be of clinical benefit. In this manuscript, we review the available data on the role of ILCs in MM immunology and therapy.

Recent Insights into the Management of Inflammation in Asthma.

The present prevailing inflammatory paradigm in asthma is of T2-high inflammation orchestrated by key inflammatory cells like Type 2 helper lymphocytes, innate lymphoid cells group 2 and associated cytokines. Eosinophils are key components of this T2 inflammatory pathway and have become key therapeutic targets. Real-world evidence on the predominant T2-high nature of severe asthma is emerging. Various inflammatory biomarkers have been adopted in clinical practice to aid asthma characterization including airway measures such as bronchoscopic biopsy and lavage, induced sputum analysis, and fractional exhaled nitric oxide. Blood measures like eosinophil counts have also gained widespread usage and multicomponent algorithms combining different parameters are now appearing. There is also growing interest in potential future biomarkers including exhaled volatile organic compounds, micro RNAs and urinary biomarkers. Additionally, there is a growing realisation that asthma is a heterogeneous state with numerous phenotypes and associated treatable traits. These may show particular inflammatory patterns and merit-specific management approaches that could improve asthma patient outcomes. Inhaled corticosteroids (ICS) remain the mainstay of asthma management but their use earlier in the course of disease is being advocated. Recent evidence suggests potential roles for ICS in combination with long-acting beta-agonists (LABA) for as needed use in mild asthma whilst maintenance and reliever therapy regimes have gained widespread acceptance. Other anti-inflammatory strategies including ultra-fine particle ICS, leukotriene receptor antagonists and macrolide antibiotics may show efficacy in particular phenotypes too. Monoclonal antibody biologic therapies have recently entered clinical practice with significant impacts on asthma outcomes. Understanding of the efficacy and use of those agents is becoming clearer with a growing body of real-world evidence as is their potential applicability to other treatable comorbid traits. In conclusion, the evolving understanding of T2 driven inflammation alongside a treatable traits disease model is enhancing therapeutic approaches to address inflammation in asthma.

The role of airway remodeling in the pathogenesis and treatment of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is currently considered the third leading cause of death in the world. COPD represents an important public health challenge and a socio-economical problem that is preventable and treatable. The main cause of COPD is chronic inhalation of cigarette smoke, and other harmful constituents of air pollution, which cause epithelial injury, chronic inflammation and airway remodeling. Airway remodeling is most prominent in small airways. It is due to infiltration of the airways by inflammatory cells, such as neutrophils, eosinophils, macrophages, and immune cells, including CD8+ T-cells, Th1, Th17 lymphocytes, and innate lymphoid cells group 3. Fibroblasts, myofibroblasts, and airway smooth muscle (ASM) cells also contribute to airway remodeling by depositing extracellular matrix (ECM) proteins, which increase the thickness of the airway wall. Activated inflammatory cells, and structural cells secrete cytokines, chemokines, growth factors, and enzymes which propagate airway remodeling. Airway remodeling is an active process which leads to thickness of the reticular basement membrane, subepithelial fibrosis, peribronchiolar fibrosis, and ASM cells hyperplasia and hypertrophy. It is also accompanied by submucosal glands and goblet cells hypertrophy and mucus hypersecretion, and angiogenesis. Epithelial mesenchymal transmission (EMT) plays a key role in airway remodeling. In patients with COPD and smokers, cellular reprograming in epithelial cells leads to EMT, whereby epithelial cells assume a mesencymal phenotype. Additionally, COPD is associated with increased parasympathetic cholinergic activity, which leads to ASM cells hypercontractility, increased mucus secretion, and vasodilatation. Treatment of COPD is intricate because of the heterogeneous nature of the disease, which requires specific treatment of the pathophysiological pathways, such as airway inflammation, ASM cell hypercontractility, and parasympathetic cholinergic hyperreactivity. The Global Initiative for Chronic Obstructive Lung Disease (GOLD) 2020 strategy report recommends personalized approach for the treatment of COPD. However, some patients with COPD are unresponsive to the standards of care. They may require a triple combination of LABA/LAMA/ICS. Single-inhaler triple therapy (SITT), such as fluticasone fuorate/vilanterol/umeclidinium has been shown to significantly improve symptoms and asthma control, reduce moderate and severe exacerbations, and to improve lung function.

Innate Lymphoid Cells as Regulators of Epithelial Integrity: Therapeutic Implications for Inflammatory Bowel Diseases.

The occurrence of epithelial defects in the gut relevantly contributes to the pathogenesis of inflammatory bowel diseases (IBD), whereby the impairment of intestinal epithelial barrier integrity seems to represent a primary trigger as well as a disease amplifying consequence of the chronic inflammatory process. Besides epithelial cell intrinsic factors, accumulated and overwhelmingly activated immune cells and their secretome have been identified as critical modulators of the pathologically altered intestinal epithelial cell (IEC) function in IBD. In this context, over the last 10 years increasing levels of attention have been paid to the group of innate lymphoid cells (ILCs). This is in particular due to a preferential location of these rather newly described innate immune cells in close proximity to mucosal barriers, their profound capacity to secrete effector cytokines and their numerical and functional alteration under chronic inflammatory conditions. Aiming on a comprehensive and updated summary of our current understanding of the bidirectional mucosal crosstalk between ILCs and IECs, this review article will in particular focus on the potential capacity of gut infiltrating type-1, type-2, and type-3 helper ILCs (ILC1s, ILC2s, and ILC3s, respectively) to impact on the survival, differentiation, and barrier function of IECs. Based on data acquired in IBD patients or in experimental models of colitis, we will discuss whether the different ILC subgroups could serve as potential therapeutic targets for maintenance of epithelial integrity and/or mucosal healing in IBD.

Ontogeny and heterogeneity of innate lymphoid cells and the noncoding genome.

Since their discovery a decade ago, it has become evident that innate lymphoid cells (ILCs) play critical roles in protective immune responses against intracellular and extracellular pathogens but are also central regulators of epithelial barrier integrity and tissue homeostasis. ILCs populate almost every tissue in mammalian organisms; therefore, not surprisingly, dysregulation of their functions contributes to the development and progression of multiple inflammatory and metabolic diseases. Our knowledge of the transcriptional programs governing the development, differentiation, and functions of the different groups of ILCs has increased dramatically in the last ten years. However, with the advent of new technologies, an unprecedented level of heterogeneity, plasticity, and developmental complexity has started to be revealed. In this review, we highlight recent advances in our understanding of ILC development and their biological functions. In particular, we aim to emphasize how our increasing knowledge of the chromatin landscape and the noncoding genome of these innate lymphocytes is allowing us to better understand their development and functions in different contexts during homeostasis and inflammation. Moreover, we propose that the design of more refined genetic tools to study tissue-specific ILCs and their functions can be accomplished by leveraging our understanding of how specific noncoding elements of the genome regulate gene expression in ILCs.

The impact of fungal allergic sensitization on asthma.

Fungal sensitization may contribute to the development of asthma as well as asthma severity. The purpose of this review is to summarize existing knowledge about the pathophysiology, diagnosis, and management of fungal sensitization in asthma and highlight unmet needs and target areas for future investigation. Fungal sensitization may occur by a normal or aberrant immune response. Allergic sensitization to fungi is mediated by the adaptive immune response driven by TH2 cells and the innate immune response driven by the innate lymphoid cells group 2. Diagnosis of fungal sensitization can be made by either skin prick testing or measurement of fungal-specific serum IgE. Fungal sensitization in asthma has been associated with worse disease severity, including reduced lung function, increased risk of hospitalizations, and life-threatening asthma. A spectrum of disease related to fungal sensitization has been described in asthma including allergic bronchopulmonary mycosis and severe asthma with fungal sensitization (SAFS). The role of antifungals and targeted biologic therapy in asthma with fungal sensitization need further investigation. There is increasing awareness of the contribution of fungal sensitization to asthma severity. However, there are no therapies with proven efficacy. Randomized clinical trials are needed to further investigate the role of biologics.

Abstract 3310: Resolving the heterogeneity of human circulating innate lymphoid cells via simultaneous, high-dimensional analysis of protein and gene expression

Abstract Cancer treatment has been revolutionized with the development of immunomodulatory therapies. These therapies have primarily focused on enhancing T-cell responses: whether it is unleashing T cells through blockade of regulatory checkpoint inhibitors or generation of chimeric antigen receptor (CAR) T cells. However, there has been recent interest in harnessing the immunotherapeutic potential of other cytotoxic cells such as Natural Killer (NK) cells. Similar to NK cells, innate lymphoid cells (ILCs) may offer another target of these immunotherapy approaches. Before the potential of these cells can be realized, there is a need for better understanding of these recently described cell populations. ILCs act as the immune system's first responders and have been shown to play a key role in tissue homeostasis, chronic inflammation and cancer. Three main groups of non-cytotoxic ILCs (ILC1, ILC2 and ILC3) have been broadly defined based on developmental trajectories and function, driven by expression of specific transcription factors. Deeper characterization of these cells through either high parameter protein analysis or single-cell RNA sequencing has revealed a more complex and heterogeneous nature of ILCs across different tissues and donors. Therefore, the identity of ILCs is still elusive and controversial. In this study, we developed a comprehensive approach to further refine the signatures of human circulating ILC subsets. Total ILCs (Lineage- CD127+ cells) were enriched from 4 normal donors by flow sorting using the BD FACSAria™ Fusion cell sorter and processed for downstream single-cell multiomic characterization. BD® AbSeq reagents and a targeted BD Rhapsody™ Immune Response Panel were used to enable simultaneous detection of 42 proteins and 399 genes using the BD Rhapsody™ Single-Cell Analysis System. Differential protein and gene expression analysis in addition to combinatorial expression of CD294 and CD117 confirmed 3 conventional ILC populations as well as the signatures of three distinct subsets within ILC1. This discovery approach provided information about relative expression of a small selection of proteins or surface marker-coding genes that enable the discrimination of these ILC subsets. These data were used to design high-parameter flow cytometry panels for high-throughput analysis of different healthy donors. ILC subsets differentially distributed across donors were detected and defined using unsupervised computational analysis confirming the result of multiomic analysis, while the functional and biological relevance of the identified subsets remains to be assessed. For Research Use Only. Not for use in diagnostic or therapeutic procedures. Class 1 laser product. BD, the BD Logo, FACSymphony and Rhapsody are trademarks of Becton, Dickinson and Company or its affiliates. © 2019 BD. All rights reserved. Citation Format: Aaron J. Tyznik, Mirko Corselli, Gisle V. Baracho, Chip Lomas, Silin Sa, Stephanie Widmann, Suraj Saksena, Smita Ghanekar. Resolving the heterogeneity of human circulating innate lymphoid cells via simultaneous, high-dimensional analysis of protein and gene expression [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3310.

Cobalt exposure via skin alters lung immune cells and enhances pulmonary responses to cobalt in mice.

Cobalt has been associated with allergic contact dermatitis and occupational asthma. However, the link between skin exposure and lung responses to cobalt is currently unknown. We investigated the effect of prior dermal sensitization to cobalt on pulmonary physiological and immunological responses after subsequent challenge with cobalt via the airways. BALB/c mice received epicutaneous applications (25 μL/ear) with 5% CoCl2*6H2O (Co) or the vehicle (Veh) dimethyl sulfoxide (DMSO) twice; they then received oropharyngeal challenges with 0.05% CoCl2*6H2O or saline five times, thereby obtaining four groups: Veh/Veh, Co/Veh, Veh/Co, and Co/Co. To detect early respiratory responses noninvasively, we performed sequential in vivo microcomputed tomography (µCT). One day after the last challenge, we assessed airway hyperreactivity (AHR) to methacholine, inflammation in bronchoalveolar lavage (BAL), innate lymphoid cells (ILCs) and dendritic cells (DCs) in the lungs, and serum IgE. Compared with the Veh/Veh group, the Co/Co group showed increased µCT-derived lung response, increased AHR to methacholine, mixed neutrophilic and eosinophilic inflammation, elevated monocyte chemoattractant protein-1 (MCP-1), and elevated keratinocyte chemoattractant (KC) in BAL. Flow cytometry in the Co/Co group demonstrated increased DC, type 1 and type 2 conventional DC (cDC1/cDC2), monocyte-derived DC, increased ILC group 2, and natural cytotoxicity receptor-ILC group 3. The Veh/Co group showed only increased AHR to methacholine and elevated MCP-1 in BAL, whereas the Co/Veh group showed increased cDC1 and ILC2 in lung. We conclude that dermal sensitization to cobalt may increase the susceptibility of the lungs to inhaling cobalt. Mechanistically, this enhanced susceptibility involves changes in pulmonary DCs and ILCs.

IL-22 promotes tumor growth of breast cancer cells in mice.

Increased interleukin-22 (IL-22) level was reported to associate with progression of breast cancer. Regulation of IL-22 in breast cancer still needs to be elucidated. We assessed the effect of giving IL-22 in tumor growth of mice inoculated with 4T1, MCF7 and MDA-MB-231 breast cancer cells. IL-22-producing cells were analyzed in tumor tissues. We also analyzed the impact of giving IL-1β and IL-23 on IL-22 levels in tumor tissues. Giving exogenous IL-22 increased tumor size and intra-tumor Ki-67-positive cells in vivo. IL-22 increased phosphorylated STAT3 level and proliferation of breast cancer cells in vitro, an effect blocked by a STAT3-inhibitor stattic. Endogenous IL-22 mRNA level was up-regulated in tumor tissue, compared with normal mammary tissue. Innate lymphoid cell group 3 (ILC3) is a major producer of IL-22 in 4T1 tumor. Giving IL-1β and/or IL-23 increased cell proliferation in 4T1 tumor, which was reversed by concurrent use of an IL-22 neutralization antibody. IL-1β and IL-23 increased levels of IL-22 mRNA and IL-22-producing ILC3 in 4T1 tumor. Our findings suggest a mechanism for how IL-22 regulates tumor growth in breast cancer, and indicate blocking IL-22 function might reduce IL-1β- and IL-23-induced tumor progression of breast cancer.

Targeted deletion of NFAT-Interacting-Protein-(NIP) 45 resolves experimental asthma by inhibiting Innate Lymphoid Cells group 2 (ILC2)

Here we investigated the role of NFAT-interacting protein (NIP)-45, an Interleukin (IL)-4 inducing Transcription Factor, and its impact on the differentiation of Group 2 Innate -Lymphoid -Cells (ILC2s) in the pathogenesis of asthma. NIP45, a transcription factor regulating NFATc1 activity, mRNA was found to be induced in the Peripheral Blood mononuclear cells (PMBCs) of asthmatic pre-school children with allergies and in the peripheral blood CD4+ T cells from adult asthmatic patients. In PBMCs of asthmatic and control children, NIP45 mRNA directly correlated with NFATc1 but not with T-bet. Targeted deletion of NIP45 in mice resulted in a protective phenotype in experimental asthma with reduced airway mucus production, airway hyperresponsiveness and eosinophils. This phenotype was reversed by intranasal delivery of recombinant r-IL-33. Consistently, ILC2s and not GATA3+ CD4+ T-cells were decreased in the lungs of asthmatic NIP45−/− mice. Reduced cell number spleen ILC2s could be differentiated from NIP45−/− as compared to wild-type mice after in vivo injection of a microcircle-DNA vector expressing IL-25 and decreased cytokines and ILC2 markers in ILC2 differentiated from the bone marrow of NIP45−/− mice. NIP45 thus emerges as a new therapeutic target for the resolution of the airway pathology, down-regulation of ILC2s and mucus production in asthma.

Filming the airways

Innate Lymphoid Cells Group 2 innate lymphoid cells (ILC2s) are key drivers of immune responses in the lung. Puttur et al. used an interleukin-13 (IL-13) reporter mouse strain to visualize migration of ILC2s in allergic airway inflammation. ILC2s exhibited dynamic ameboid-like movement in response to IL-33. IL-3 induced up-regulation of chemokine receptor 8 on ILC2s, which promoted their homing to deposits of chemokine ligand 8 within the airways. Collagen-I, a component of the extracellular matrix (ECM), played a role in directly regulating ILC2 cell migration. Thus, structural cues from the ECM work in conjunction with immune mediators to influence immune cell functions in tissues. Sci. Immunol. 4 , eaav7638 (2019).

The balance of power: innate lymphoid cells in tissue inflammation and repair.

Over the last ten years, immunologists have recognized the central importance of an emerging group of innate lymphoid cells (ILCs) in health and disease. Characterization of these cells has provided a molecular definition of ILCs and their tissue-specific functions. Although the lineage-defining transcription factors, cytokine production, and nomenclature parallel those of T helper cells, ILCs do not require adaptive immune programming. Both environmental and host-derived signals shape the function of these evolutionarily ancient cells, which provide pathogen protection and promote tissue restoration. As such, ILCs function as a double-edged sword, balancing the inflammatory and reparative responses that arise during injury and disease. This Review highlights our recent understanding of tissue-resident ILCs and the signals that regulate their contribution to inflammation and tissue repair in health and disease.

Heterogeneity of NK Cells and Other Innate Lymphoid Cells in Human and Murine Decidua.

Innate lymphoid cells (ILCs) represent a heterogeneous group of cells lacking genetically rearranged antigen receptors that derive from common lymphoid progenitors. Five major groups of ILCs have been defined based on their cytokine production pattern and developmental transcription factor requirements: namely, natural killer (NK) cells, ILC1s, ILC2s, ILC3s, and lymphoid tissue-inducer (LTi) cells. ILC1s, ILC2s, and ILC3s mirror the corresponding T helper subsets (Th1, Th2, and Th17, respectively) and produce cytokines involved in defense against pathogens, lymphoid organogenesis, and tissue remodeling. During the first trimester of pregnancy, decidual tissues contain high proportion of decidual NK (dNK) cells, representing up to 50% of decidual lymphocytes, and ILC3s. They release peculiar cytokines and chemokines that contribute to successful pregnancy. Recent studies revealed that ILCs display a high degree of plasticity allowing their prompt adaptation to environmental changes. Decidual NK cells may derive from peripheral blood NK cells migrated when pregnancy establishes or from in situ differentiation of hematopoietic precursors. Previous studies showed that human and murine decidua contain dNK cells, tissue resident NK cells, and ILC3s, all characterized by unique phenotypic and functional properties, most likely induced by decidual microenvironment to favor the establishment and the maintenance of pregnancy. Thus, during the early phase of pregnancy, the simultaneous presence of different ILC subsets further underscores the complexity of the cellular components of decidual tissues as well as the role of decidual microenvironment in shaping the plasticity and the function of ILCs.

DIFFERENTIATION OF NK CELLS. A LOOK THROUGH THE PRISM OF TRANSCRIPTION FACTORS AND INTRACELLULAR MESSENGERS

All lymphoid cells are referred to as an innate or adaptive immunity unit in terms of the mechanisms of performing immune reactions. The functional activity of natural killer (NK) cells is not associated with pre-activation processes resulting from contact with antigen, rearrangement of antigen-recognition receptor genes, and clonal proliferation. In this regard, NK cells are traditionally referred to as cells of innate immunity. Previously, it was believed that NK cells represent the only population of innate immunity lymphoid cells, but, more recently, there has been increasing evidence in the literature concerning existence of different populations of these cells, thus serving a basis for isolating a common cluster called Innate Lymphoid Cells (ILC). According to the ILC classification, NK cells are classified as the first group of innate lymphoid cells according to their overall functional characteristics, as well as contribution of the T-bet transcription factor to their differentiation. Complexity, multistage and partially nonlinear character of NK cell differentiation are associated with influence of the cellular microenvironment, consistent expression of transcription factors and activation of various intracellular signaling pathways in NK cells. The review considers positioning of NK cells in the ILC classification, the main transcription factors involved in NK cell differentiation. The authors are seeking for generalization of the major routes of intracellular signal transmission in NK cells depending on their activation by cytokines located in the cellular microenvironment and affecting NK cells. The decidual NK cells during pregnancy represent a special object of NK cell differentiation. Stromal cells, trophoblast cells and macrophages are present in the decidua, in addition to NK cells. The review concerns a special case of microenvironmental effects upon expression of transcription factors and activation of NK intracellular messengers, while considering trophoblast cells an example of such influences. The recently discovered variety of NK cells, induced by the microenvironment in the course of their differentiation, requires further study.