Cytokine-Mediated Regulation of Innate Lymphoid Cell Plasticity in Gut Mucosal Immunity

Lung type 3 innate lymphoid cells respond early following Mycobacterium tuberculosis infection

Tuberculosis is the leading cause of death due to an infectious disease worldwide. Innate lymphoid type 3 cells (ILC3s) mediate early protection during Mycobacterium tuberculosis (Mtb) infection. However, the early signaling mechanisms that govern ILC3 activation or recruitment within the lung during Mtb infection are unclear. scRNA-seq analysis of Mtb-infected mouse lung innate lymphoid cells (ILCs) has revealed the presence of different clusters of ILC populations, suggesting heterogeneity. Using mouse models, we show that during Mtb infection, interleukin-1 receptor (IL-1R) signaling on epithelial cells drives ILC3 expansion and regulates ILC3 accumulation in the lung. Furthermore, our data revealed that C-X-C motif chemokine receptor 5 (CXCR5) signaling plays a crucial role in ILC3 recruitment from periphery during Mtb infection. Our study thus establishes the early responses that drive ILC3 accumulation during Mtb infection and points to ILC3s as a potential vaccine target.

IMPORTANCE

Tuberculosis is a leading cause of death due to a single infectious agent accounting for 1.6 million deaths each year. In our study, we determined the role of type 3 innate lymphoid cells in early immune events necessary for achieving protection during Mtb infection. Our study reveals distinct clusters of ILC2, ILC3, and ILC3/ILC1-like cells in Mtb infection. Moreover, our study reveal that IL-1R signaling on lung type 2 epithelial cells plays a key role in lung ILC3 accumulation during Mtb infection. CXCR5 on ILC3s is involved in ILC3 homing from periphery during Mtb infection. Thus, our study provides novel insights into the early immune mechanisms governed by innate lymphoid cells that can be targeted for potential vaccine-induced protection.

PEDV promotes the differentiation of CD4+T cells towards Th1, Tfh, and Treg cells via CD103+DCs

Porcine epidemic diarrhea virus (PEDV) can infect all ages of pigs, particularly newborn piglets with a mortality almost reaching to 80-100%, causing significant economic losses to the global pig industry. The mucosal immune response is crucial for PEDV prevention, in which specific dendritic cells (DCs) and differentiated T cells play vital roles. In this study, CD103+DCs were differentiated successfully with retinoic acid (RA) treatment in vitro. PEDV could not replicate efficiently in differentiated CD103+DCs but could promote maturation of CD103+DCs by up-regulating the expression of SLA-DR, CD1a, CD86, and cytokines of IL-1β and IL-10. In addition, PEDV-infected CD103+DCs and CD4+T cells were co-cultured, and the results showed that the differentiation of CD4+T cells toward Th1, Tfh, and Treg, but not Th2. These results demonstrate that PEDV-infected CD103+DCs could promote the differentiation of CD4+T cells, which provided the basis for further study of mucosal response induced by PEDV via CD103+DCs.

Pathological mechanism and targeted drugs of ulcerative colitis: A review

Ulcerative colitis (UC) is a chronic inflammatory disease of the colon with abdominal pain, diarrhea, and mucopurulent stools as the main symptoms. Its incidence is increasing worldwide, and traditional treatments have problems such as immunosuppression and metabolic disorders. In this article, the etiology and pathogenesis of ulcerative colitis are reviewed to clarify the targeted drugs of UC in the latest research. Our aim is to provide more ideas for the clinical treatment and new drug development of UC, mainly by analyzing and sorting out the relevant literature on PubMed, summarizing and finding that it is related to the main genetic, environmental, immune and other factors, and explaining its pathogenesis from the NF-κB pathway, PI3K/Akt signaling pathway, and JAK/STAT signaling pathway, and obtaining anti-TNF-α monoclonal antibodies, integrin antagonists, IL-12/IL-23 antagonists, novel UC-targeted drugs such as JAK inhibitors and SIP receptor agonists. We believe that rational selection of targeted drugs and formulation of the best dosing strategy under the comprehensive consideration of clinical evaluation is the best way to treat UC.

The immunity modulation of transforming growth factor-β in malaria and other pathological process

The main causative agent of malaria in humans is Plasmodium falciparum, which is spread through biting Anopheles mosquitoes. Immunoregulation in the host involving the pleiotropic cytokine transforming growth factor-β (TGF-β) has a vital role in controlling the immune response to P. falciparum infection. Based on a search of the published literature, this study investigated the correlation between malaria and immune cells, specifically the role of TGF-β in the immune response. The studies analyzed showed that, when present in low amounts, TGF-β promotes inflammation, but inhibits inflammation when present in high concentrations; thus, it is an essential regulator of inflammation. It has also been shown that the quantity of TGF-β produced by the host can influence how badly the parasite affects the host. Low levels of TGF-β in the host prevent the host from being able to manage the inflammation that Plasmodium causes, which results in a pathological situation that leaves the host vulnerable to fatal infection. Additionally, the amount of TGF-β fluctuates throughout the host's Plasmodium infection. At the beginning of a Plasmodium infection, TGF-β levels are noticeably increased, and as Plasmodium multiplies quickly, they start to decline, hindering further growth. In addition, it is also involved in the growth, proliferation, and operation of various types of immune cell and correlated with levels of cytokines associated with the immune response to malaria. TGF-β levels were positively connected with the anti-inflammatory cytokine interleukin-10 (IL-10), but negatively correlated with the proinflammatory cytokines interferon-γ (IFN-γ) and IL-6 in individuals with severe malaria. Thus, TGF-β might balance immune-mediated pathological damage and the regulation and clearance of infectious pathogens. Numerous domestic and international studies have demonstrated that TGF-β maintains a dynamic balance between anti-inflammation and pro-inflammation in malaria immunity by acting as an anti-inflammatory factor when inflammation levels are too high and as a pro-inflammatory factor when inflammation levels are deficient. Such information could be of relevance to the design of urgently needed vaccines and medications to meet the emerging risks associated with the increasing spread of malaria and the development of drug resistance.

Parallel origins and functions of T cells and ILCs

Innate lymphoid cells (ILCs) are tissue resident cells that are triggered through a relatively broad spectrum of alarmins, inflammatory cues, neuropeptides, and hormones. Functionally, ILCs are akin to subsets of helper T cells and are characterized by a similar effector cytokine profile. They also share a dependency on many of the same essential transcription factors identified for the maintenance and survival of T cells. The key distinguishing factor between the ILC family and T cells is the lack of antigen-specific T cell receptor (TCR) on ILCs and, thus, they can be considered the "ultimate invariant T cells". ILCs, like T cells, orchestrate downstream effector inflammatory responses by adjusting the cytokine microenvironment in a fashion that promotes protection, health, and homeostasis at mucosal barrier sites. But also, like T cells, ILCs have recently been implicated in several pathological inflammatory disease states. This review focuses on the selective role of ILCs in the development of allergic airway inflammation (AAI) and fibrosis in the gut where a complex ILC interplay has been shown to either attenuate or worsen disease. Finally, we discuss new data on TCR gene rearrangements in subsets of ILCs that challenge the current dogma linking their origin to committed bone marrow progenitors and instead propose a thymic origin for at least some ILCs. In addition, we highlight how naturally occurring TCR rearrangements and the expression of major histocompatibility (MHC) molecules in ILCs provide a useful natural barcode for these cells and may prove instrumental in studying their origins and plasticity.

CD226 deficiency exacerbated intestinal immune dysregulation in mice with dinitrochlorobenzene-induced atopic dermatitis

Intestinal mucosal immunity plays a pivotal role in host defence. In this study, we found that cluster of differentiation 226 (CD226) gene knockout (KO) led to more severe atopic dermatitis (AD)-related skin pathologies and bowel abnormalities in a 2,4-dinitrochlorobenzene (DNCB)-induced AD-like mouse model. Following DNCB administration, the expression of CD226 was elevated in intestinal mucosal tissues, including group 3 innate lymphoid cells (ILC3s) and CD4⁺ T cells of Peyer's patches (PPs). CD226 deficiency led to an overactive intestinal immune response in the AD-like mice, as evidenced by increased inflammation and Th1/Th2-related cytokine levels as well as increased Paneth cell numbers and antimicrobial peptide (AMP) expression, which was likely due to the higher interleukin (IL)-22 production in the lamina propria. Additionally, CD226 deficiency increased the production of IL-4 and IL-17 in mesenteric lymph nodes as well as the number of PPs and expression of immunoglobulin (Ig) A in B cells. Moreover, insufficient expression of CD226 affected the characterization of intraepithelial and lamina propria lymphocytes in the intestinal mucosa. Finally, the number of PPs was increased in CD4⁺ T cell-specific CD226 KO and regulatory T (Treg) cell-specific CD226 KO mice; thus, loss of CD226 in Treg cells resulted in impaired Treg cell-suppressive function. Therefore, our findings indicate that CD226 deficiency alters intestinal immune functionality in inflammatory diseases.

Innate Lymphoid Cell Plasticity in Mucosal Infections

Mucosal tissue homeostasis is a dynamic process that involves multiple mechanisms including regulation of innate lymphoid cells (ILCs). ILCs are mostly tissue-resident cells which are critical for tissue homeostasis and immune response against pathogens. ILCs can sense environmental changes and rapidly respond by producing effector cytokines to limit pathogen spread and initiate tissue recovery. However, dysregulation of ILCs can also lead to immunopathology. Accumulating evidence suggests that ILCs are dynamic population that can change their phenotype and functions under rapidly changing tissue microenvironment. However, the significance of ILC plasticity in response to pathogens remains poorly understood. Therefore, in this review, we discuss recent advances in understanding the mechanisms regulating ILC plasticity in response to intestinal, respiratory and genital tract pathogens. Key transcription factors and lineage-guiding cytokines regulate this plasticity. Additionally, we discuss the emerging data on the role of tissue microenvironment, gut microbiota, and hypoxia in ILC plasticity in response to mucosal pathogens. The identification of new pathways and molecular mechanisms that control functions and plasticity of ILCs could uncover more specific and effective therapeutic targets for infectious and autoimmune diseases where ILCs become dysregulated.

Repetitive Exposure to Bacteriophage Cocktails against Pseudomonas aeruginosa or Escherichia coli Provokes Marginal Humoral Immunity in Naïve Mice

Phage therapy of ventilator-associated pneumonia (VAP) is of great interest due to the rising incidence of multidrug-resistant bacterial pathogens. However, natural or therapy-induced immunity against therapeutic phages remains a potential concern. In this study, we investigated the innate and adaptive immune responses to two different phage cocktails targeting either Pseudomonas aeruginosa or Escherichia coli-two VAP-associated pathogens-in naïve mice without the confounding effects of a bacterial infection. Active or UV-inactivated phage cocktails or buffers were injected intraperitoneally daily for 7 days in C57BL/6J wild-type mice. Blood cell analysis, flow cytometry analysis, assessment of phage distribution and histopathological analysis of spleens were performed at 6 h, 10 days and 21 days after treatment start. Phages reached the lungs and although the phage cocktails were slightly immunogenic, phage injections were well tolerated without obvious adverse effects. No signs of activation of innate or adaptive immune cells were observed; however, both active phage cocktails elicited a minimal humoral response with secretion of phage-specific antibodies. Our findings show that even repetitive injections lead only to a minimal innate and adaptive immune response in naïve mice and suggest that systemic phage treatment is thus potentially suitable for treating bacterial lung infections.

Distinct subsets of innate lymphoid cells in nasal polyp

BACKGROUND

Group 2 innate lymphoid cells (ILC2s) contribute to the pathogenesis of eosinophilic chronic rhinosinusitis with nasal polyps (CRSwNPs). However, the role of other subsets of ILCs and the differentiation of ILCs in CRSwNPs is not well understood. This study aimed to characterize the ILC subsets and evaluate the differentiation of ILCs from ILC precursors (ILCPs) in NP tissue.

METHODS

ILC subsets and ILCPs were evaluated by flow cytometry in fresh sinonasal mucosa from patients with CRSwNPs and control subjects. Subsets were compared based on clinical variables and immunological features of the patients. Sorted ILCPs (Lin^-CD127⁺CD117⁺CD45RA⁺IL1R1⁺) were cultured with cytokines.

RESULTS

The frequency of ILC1s and IFN-γ-producing ILC1s increased in non-eosinophilic NPs, whereas that of ILC2s and IL-5-producing ILC2s increased in eosinophilic NPs, particularly in patients with comorbid asthma. The frequency of ILC1s and IFN-γ-producing ILC1s, and frequency of ILC2s and IL-5-producing ILC2s positively correlated with that of neutrophils and eosinophils, respectively. The proportion of IFN-γ-producing ILC1s positively correlated with clinical severity and levels of IFN-γ and IL-8. The proportion of IL-5-producing ILC2s positively correlated with levels of IL-5, CCL24, and total IgE. ILCPs were identified in NP tissue and differentiated into IFN-γ-producing or IL-5-producing ILCs in response to increased IL-12 and IL-18 or IL-25 and IL-33 in non-eosinophilic NPs and eosinophilic NPs, respectively.

CONCLUSIONS

ILC1s and ILC2s may be associated with neutrophilic and eosinophilic inflammation in CRSwNPs, respectively. In addition, ILCPs located in the sinus mucosa could differentiate into IFN-γ- or IL-5-producing cells in response to local cytokine stimuli.

The soldiers needed to be awakened: Tumor-infiltrating immune cells

In the tumor microenvironment, tumor-infiltrating immune cells (TIICs) are a key component. Different types of TIICs play distinct roles. CD8+ T cells and natural killer (NK) cells could secrete soluble factors to hinder tumor cell growth, whereas regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) release inhibitory factors to promote tumor growth and progression. In the meantime, a growing body of evidence illustrates that the balance between pro- and anti-tumor responses of TIICs is associated with the prognosis in the tumor microenvironment. Therefore, in order to boost anti-tumor response and improve the clinical outcome of tumor patients, a variety of anti-tumor strategies for targeting TIICs based on their respective functions have been developed and obtained good treatment benefits, including mainly immune checkpoint blockade (ICB), adoptive cell therapies (ACT), chimeric antigen receptor (CAR) T cells, and various monoclonal antibodies. In recent years, the tumor-specific features of immune cells are further investigated by various methods, such as using single-cell RNA sequencing (scRNA-seq), and the results indicate that these cells have diverse phenotypes in different types of tumors and emerge inconsistent therapeutic responses. Hence, we concluded the recent advances in tumor-infiltrating immune cells, including functions, prognostic values, and various immunotherapy strategies for each immune cell in different tumors.

Genomic and Transcriptional Mechanisms Governing Innate-like T Lymphocyte Development

Innate-like lymphocytes are a subset of lymphoid cells that function as a first line of defense against microbial infection. These cells are activated by proinflammatory cytokines or broadly expressed receptors and are able to rapidly perform their effector functions owing to a uniquely primed chromatin state that is acquired as a part of their developmental program. These cells function in many organs to protect against disease, but they release cytokines and cytotoxic mediators that can also lead to severe tissue pathologies. Therefore, harnessing the capabilities of these cells for therapeutic interventions will require a deep understanding of how these cells develop and regulate their effector functions. In this review we discuss recent advances in the identification of the transcription factors and the genomic regions that guide the development and function of invariant NKT cells and we highlight related mechanisms in other innate-like lymphocytes.

Heterogeneity of ILC2s in the Intestine; Homeostasis and Pathology

Group 2 innate lymphoid cells (ILC2s) were identified in 2010 as a novel lymphocyte subset lacking antigen receptors, such as T-cell or B-cell receptors. ILC2s induce local immune responses characterized by producing type 2 cytokines and play essential roles for maintaining tissue homeostasis. ILC2s are distributed across various organs, including the intestine where immune cells are continuously exposed to external antigens. Followed by luminal antigen stimulation, intestinal epithelial cells produce alarmins, such as IL-25, IL-33, and thymic stromal lymphopoietin, and activate ILC2s to expand and produce cytokines. In the context of parasite infection, the tuft cell lining in the epithelium has been revealed as a dominant source of intestinal IL-25 and possesses the capability to regulate ILC2 homeostasis. Neuronal systems also regulate ILC2s through neuropeptides and neurotransmitters, and interact with ILC2s bidirectionally, a process termed “neuro-immune crosstalk”. Activated ILC2s produce type 2 cytokines, which contribute to epithelial barrier function, clearance of luminal antigens and tissue repair, while ILC2s are also involved in chronic inflammation and tissue fibrosis. Recent studies have shed light on the contribution of ILC2s to inflammatory bowel diseases, mainly comprising ulcerative colitis and Crohn’s disease, as defined by chronic immune activation and inflammation. Modern single-cell analysis techniques provide a tissue-specific picture of ILC2s and their roles in regulating homeostasis in each organ. Particularly, single-cell analysis helps our understanding of the uniqueness and commonness of ILC2s across tissues and opens the novel research area of ILC2 heterogeneity. ILC2s are classified into different phenotypes depending on tissue and phase of inflammation, mainly inflammatory and natural ILC2 cells. ILC2s can also switch phenotype to ILC1- or ILC3-like subsets. Hence, recent studies have revealed the heterogeneity and plasticity of ILC2, which indicate dynamicity of inflammation and the immune system. In this review, we describe the regulatory mechanisms, function, and pathological roles of ILC2s in the intestine.

Innate Lymphoid Cells in Intestinal Homeostasis and Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a heterogeneous state of chronic intestinal inflammation of unknown cause encompassing Crohn’s disease (CD) and ulcerative colitis (UC). IBD has been linked to genetic and environmental factors, microbiota dysbiosis, exacerbated innate and adaptive immunity and epithelial intestinal barrier dysfunction. IBD is classically associated with gut accumulation of proinflammatory Th1 and Th17 cells accompanied by insufficient Treg numbers and Tr1 immune suppression. Inflammatory T cells guide innate cells to perpetuate a constant hypersensitivity to microbial antigens, tissue injury and chronic intestinal inflammation. Recent studies of intestinal mucosal homeostasis and IBD suggest involvement of innate lymphoid cells (ILCs). These lymphoid-origin cells are innate counterparts of T cells but lack the antigen receptors expressed on B and T cells. ILCs play important roles in the first line of antimicrobial defense and contribute to organ development, tissue protection and regeneration, and mucosal homeostasis by maintaining the balance between antipathogen immunity and commensal tolerance. Intestinal homeostasis requires strict regulation of the quantity and activity of local ILC subpopulations. Recent studies demonstrated that changes to ILCs during IBD contribute to disease development. A better understanding of ILC behavior in gastrointestinal homeostasis and inflammation will provide valuable insights into new approaches to IBD treatment. This review summarizes recent research into ILCs in intestinal homeostasis and the latest advances in the understanding of the role of ILCs in IBD, with particular emphasis on the interaction between microbiota and ILC populations and functions.

A crosstalk between type 2 innate lymphoid cells and alternative macrophages in lung development and lung diseases (Review)

Type 2 innate lymphoid cells (ILC2s) are important innate immune cells that are involved in type 2 inflammation, in both mice and humans. ILC2s are stimulated by factors, including interleukin (IL)-33 and IL-25, and activated ILC2s secrete several cytokines that mediate type 2 immunity by inducing profound changes in physiology, including activation of alternative (M2) macrophages. M2 macrophages possess immune modulatory, phagocytic, tissue repair and remodeling properties, and can regulate ILC2s under infection. The present review summarizes the role of ILC2s as innate cells and M2 macrophages as anti-inflammatory cells, and discusses current literature on their important biological significance. The present review also highlights how the crosstalk between ILC2s and M2 macrophages contributes to lung development, induces pulmonary parasitic expulsion, exacerbates pulmonary viral and fungal infections and allergic airway diseases, and promotes the development of lung diseases, such as pulmonary fibrosis, chronic obstructive pulmonary disease and carcinoma of the lungs.