LAIR-1 Limits Neutrophilic Airway Inflammation

Mechanistic role of FN1 in LAIR-1 mediated downregulation of ovarian cancer cell proliferation

OBJECTIVE

RNA-seq was used to explore the potential mechanism underlying human leukocyte-associated immunoglobulin-like receptor 1 (LAIR-1) inhibition of the proliferation and migration of ovarian cancer cells.

METHOD

A LAIR-1-overexpression cell model was established using a LAIR-1-lentivirus. After confirming and identifying the LAIR-1 expression cell clones by flow cytometry and RT-qPCR, the proliferation and migration of the cells were examined by CCK8 and scratch assays, and the differentially expressed genes (DEGs) were searched by RNA-seq and analyzed by GO and KEGG enrichment. String was used for protein interaction network analysis, and Cytoscape was used to identify key proteins.

RESULTS

LAIR-1 inhibited the proliferation and migration of ovarian cancer cells. LAIR-1 expression caused the upregulation of 83 genes and the downregulation of 80 genes. Among the DEGs, fibronectin 1 (FN1) was a key protein affecting the downstream FAK-MEK-ERK axis. KEGG enrichment analysis identified the MAPK pathway as the most obvious enrichment pathway, followed by PI3K-AKT pathway.

CONCLUSION

LAIR-1 downregulates FN1 to inhibit the FAK-MEK-ERK axis, as well as the proliferation and migration of ovarian cancer cells.

Identification of Protein Networks and Biological Pathways Driving the Progression of Atherosclerosis in Human Carotid Arteries Through Mass Spectrometry-Based Proteomics

Vulnerable atherosclerotic plaques, especially hemorrhaged lesions, are the major cause of mortalities related to vascular pathologies. The early identification of vulnerable plaques helps to stratify patients at risk of developing acute vascular events. In this study, proteomics analyses of human carotid artery samples collected from patients with atheromatous plaques and complicated lesions, respectively, as well as from healthy controls were performed. The proteins isolated from the carotid artery samples were analyzed by a bottom-up shotgun approach that relied on nanoflow liquid chromatography-tandem mass spectrometry analyses (LC-MS/MS) using both data-dependent (DDA) and data-independent (DIA) acquisitions. The data obtained by high-resolution DIA analyses displayed a stronger distinction among groups compared to DDA analyses. Differentially expressed proteins were further examined using Ingenuity Pathway Analysis® with focus on pathological and molecular processes driving atherosclerosis. From the more than 150 significantly regulated canonical pathways, atherosclerosis signaling and neutrophil extracellular trap signaling were verified by protein-targeted data extraction. The results of our study are expected to facilitate a better understanding of the disease progression's molecular drivers and provide inspiration for further multiomics and hypothesis-driven studies.

DUSP6 protein action and related hub genes prevention of sepsis-induced lung injury were screened by WGCNA and Venn

During a sepsis infection, the lung is extremely susceptible to damage. A condition known as acute respiratory distress syndrome (ARDS) may develop in extreme circumstances. The primary objective of this research is to identify important genes that are related with both sepsis and lung injury. These genes have the potential to act as novel biomarkers in the investigation of sepsis-induced lung injury prevention strategies. It was possible to download from GEO data both the sepsis-related dataset (GSE64457) and the lung injury-related dataset (GSE40839). In the GSE64457 dataset, using the "limma" package in R revealed 429 differentially expressed genes (DEGs) with logFC values more than or equal to -1 and p values <0.05. There were 266 genes that were up-regulated and 163 genes that were down-regulated. Through the use of Gene Ontology (GO), it was discovered that the majority of the DEGs were associated with the inflammatory response (BP terms), a particular granule lumen (CC terms), and protein binding (MF terms). By doing a pathway enrichment analysis using the Kyoto Encyclopedia of Genes and Genomes (KEGG), researchers were able to identify DEGs that were mostly associated with the NOD-like receptor signalling pathway, the TNF signalling pathway, and Epstein-Barr virus infection. Within the GSE40839 dataset, Weighted Gene Co-Expression Network Analysis (WGCNA) yielded a total of 7 modules, from which it was possible to screen out 2 critical modules and 693 key genes. The important genes and DEGs were both subjected to a Venn analysis. Finally, 14 genes that overlapped (ARL4A, LAIR1, MTHFD2, TSPAN13, DUSP6, PECR, CBS, TES, ASNS, SYNE1, FGF13, LCN2, KLF10, BCAT1) were closely associated to the incidence and development of sepsis-induced lung injury. This indicates that these genes are the essential genes to avoid the occurrence of sepsis-induced lung injury. This study provides novel strategies for preventing lung harm brought on by sepsis.

CD305 participates in abnormal activation of memory CD4+ T cells in patients with RA and attenuates collagen-induced arthritis

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease that mainly affects the joints. Studies have shown that memory CD4+ T cells play an important role in the pathogenesis of RA. This study investigated the expression and function of CD305 on human memory CD4+ T cells and the effects of CD305 activating antibody on collagen-induced arthritis. The results showed that CD305 expression was significantly decreased on circulating memory CD4+ T cells from patients with RA and its mean fluorescence intensity (MFI) was negatively correlated with DAS28. Moreover, CD305 inhibited the activation of memory CD4+ T cells by down-regulating CD69 and CD25 and the production of IFN-γ, IL-4, and IL-17A induced by anti-CD3/CD28 antibodies. In addition, activation of CD305 inhibited the severity of disease in collagen-induced arthritis. In summary, CD305 reduction may mediate the excessive activation of memory CD4+ T cells and participate in the development of RA. It can be used as a predictive marker of disease activity and has potential medicinal value in the treatment of RA.

LAIR1 prevents excess inflammatory tissue damage in S. aureus skin infection and Cutaneous T-cell Lymphoma

Patients with cutaneous T cell lymphoma (CTCL) experience high morbidity and mortality due to S. aureus skin infections and sepsis, but the causative immune defect is unclear. We previously identified high levels of LAIR2, a decoy protein for the inhibitory receptor LAIR1, in advanced CTCL. Mice do not have a LAIR2 homolog, so we used Lair1 knock-out (KO) mice to model LAIR2 overexpression. In a model of subcutaneous S. aureus skin infection, Lair1 KO mice had significantly larger abscesses and areas of dermonecrosis compared to WT. Lair1 KO exhibited a pattern of increased inflammatory responses in infection and sterile immune stimulation, including increased production of proinflammatory cytokines and myeloid chemokines, neutrophil ROS, and collagen/ECM remodeling pathways. Notably, Lair1 KO infected skin had a similar bacterial burden and neutrophils and monocytes had equivalent S. aureus phagocytosis compared to WT. These findings support a model in which lack of LAIR1 signaling causes an excessive inflammatory response that does not improve infection control. CTCL skin lesions harbored similar patterns of increased expression in cytokine and collagen/ECM remodeling pathways, suggesting that high levels of LAIR2 in CTCL recapitulates Lair1 KO, causing inflammatory tissue damage and compromising host defense against S. aureus infection.

An inflammation resolution-promoting intervention prevents atrial fibrillation caused by left ventricular dysfunction

AIMS

Recent studies suggest that bioactive mediators called resolvins promote an active resolution of inflammation. Inflammatory signalling is involved in the development of the substrate for atrial fibrillation (AF). The aim of this study is to evaluate the effects of resolvin-D1 on atrial arrhythmogenic remodelling resulting from left ventricular (LV) dysfunction induced by myocardial infarction (MI) in rats.

METHODS AND RESULTS

MI was produced by left anterior descending coronary artery ligation. Intervention groups received daily intraperitoneal resolvin-D1, beginning before MI surgery (early-RvD1) or Day 7 post-MI (late-RvD1) and continued until Day 21 post-MI. AF vulnerability was evaluated by performing an electrophysiological study. Atrial conduction was analysed by using optical mapping. Fibrosis was quantified by Masson's trichrome staining and gene expression by quantitative polymerase chain reaction and RNA sequencing. Investigators were blinded to group identity. Early-RvD1 significantly reduced MI size (17 ± 6%, vs. 39 ± 6% in vehicle-MI) and preserved LV ejection fraction; these were unaffected by late-RvD1. Transoesophageal pacing induced atrial tachyarrhythmia in 2/18 (11%) sham-operated rats, vs. 18/18 (100%) MI-only rats, in 5/18 (28%, P < 0.001 vs. MI) early-RvD1 MI rats, and in 7/12 (58%, P < 0.01) late-RvD1 MI rats. Atrial conduction velocity significantly decreased post-MI, an effect suppressed by RvD1 treatment. Both early-RvD1 and late-RvD1 limited MI-induced atrial fibrosis and prevented MI-induced increases in the atrial expression of inflammation-related and fibrosis-related biomarkers and pathways.

CONCLUSIONS

RvD1 suppressed MI-related atrial arrhythmogenic remodelling. Early-RvD1 had MI sparing and atrial remodelling suppressant effects, whereas late-RvD1 attenuated atrial remodelling and AF promotion without ventricular protection, revealing atrial-protective actions unrelated to ventricular function changes. These results point to inflammation resolution-promoting compounds as novel cardio-protective interventions with a particular interest in attenuating AF substrate development.

Leukocyte-associated immunoglobulin-like receptor-1 blockade in combination with programmed death-ligand 1 targeting therapy mediates increased tumour control in mice

Collagen expression and structure in the tumour microenvironment are associated with tumour development and therapy response. Leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1) is a widely expressed inhibitory collagen receptor. LAIR-2 is a soluble homologue of LAIR-1 that competes for collagen binding. Multiple studies in mice implicate blockade of LAIR-1:collagen interaction in cancer as a promising therapeutic strategy. Here, we investigated the role of LAIR-1 in anti-tumour responses. We show that although LAIR-1 inhibits activation, proliferation, and cytokine production of mouse T cells in vitro, tumour outgrowth in LAIR-1-deficient mice did not differ from wild type mice in several in vivo tumour models. Furthermore, treatment with NC410, a LAIR-2-Fc fusion protein, did not result in increased tumour clearance in tested immunocompetent mice, which contrasts with previous data in humanized mouse models. This discrepancy may be explained by our finding that NC410 blocks human LAIR-1:collagen interaction more effectively than mouse LAIR-1:collagen interaction. Despite the lack of therapeutic impact of NC410 monotherapy, mice treated with a combination of NC410 and anti-programmed death-ligand 1 did show reduced tumour burden and increased survival. Using LAIR-1-deficient mice, we showed that this effect seemed to be dependent on the presence of LAIR-1. Taken together, our data demonstrate that the absence of LAIR-1 signalling alone is not sufficient to control tumour growth in multiple immunocompetent mouse models. However, combined targeting of LAIR-1 and PD-L1 results in increased tumour control. Thus, additional targeting of the LAIR-1:collagen pathway with NC410 is a promising approach to treating tumours where conventional immunotherapy is ineffective.

Virus-Host Protein Interaction Network of the Hepatitis E Virus ORF2-4 by Mammalian Two-Hybrid Assays

Throughout their life cycle, viruses interact with cellular host factors, thereby influencing propagation, host range, cell tropism and pathogenesis. The hepatitis E virus (HEV) is an underestimated RNA virus in which knowledge of the virus-host interaction network to date is limited. Here, two related high-throughput mammalian two-hybrid approaches (MAPPIT and KISS) were used to screen for HEV-interacting host proteins. Promising hits were examined on protein function, involved pathway(s), and their relation to other viruses. We identified 37 ORF2 hits, 187 for ORF3 and 91 for ORF4. Several hits had functions in the life cycle of distinct viruses. We focused on SHARPIN and RNF5 as candidate hits for ORF3, as they are involved in the RLR-MAVS pathway and interferon (IFN) induction during viral infections. Knocking out (KO) SHARPIN and RNF5 resulted in a different IFN response upon ORF3 transfection, compared to wild-type cells. Moreover, infection was increased in SHARPIN KO cells and decreased in RNF5 KO cells. In conclusion, MAPPIT and KISS are valuable tools to study virus-host interactions, providing insights into the poorly understood HEV life cycle. We further provide evidence for two identified hits as new host factors in the HEV life cycle.

LAIR-1 limits macrophage activation in acute inflammatory lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are serious health problems that manifest as acute respiratory failure in response to different conditions, including viral respiratory infections. Recently, the inhibitory properties of leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1) were demonstrated in allergic and viral airway inflammation. In this study, we investigate the implication of LAIR-1 in ALI/ARDS and explore the underlying mechanisms. Polyinosinic:polycytidylic acid, a synthetic analog of double-stranded RNA, was used to mimic acute inflammation in viral infections. We demonstrate that LAIR-1 is predominantly expressed on macrophages and regulates their recruitment to the lungs as well as their activation in response to polyinosinic:polycytidylic acid. Interestingly, LAIR-1 deficiency increases neutrophil recruitment as well as lung resistance and permeability. In particular, we highlight the capacity of LAIR-1 to regulate the secretion of CXCL10, considered a key marker of macrophage overactivation in acute lung inflammation. We also reveal in COVID-19-induced lung inflammation that LAIR1 is upregulated on lung macrophages in correlation with relevant immune regulatory genes. Altogether, our findings demonstrate the implication of LAIR-1 in the pathogenesis of ALI/ARDS by means of the regulation of macrophages, thereby providing the basis of a novel therapeutic target.

Inhibitory innate receptors and their potential role in transplantation

The regulatory arm of the immune system plays a crucial role in maintaining immune tolerance and preventing excessive immune responses. Immune regulation comprises various regulatory cells and molecules that work together to suppress or regulate immune responses. The programmed cell death protein 1 (PD-1) and cytotoxic T lymphocyte-associated protein 4 (CTLA-4) are examples of inhibitory receptors that counteract activating signals and fine-tune immune responses. While most of the discoveries of immune regulation have been related to T cells and the adaptive immune system, the innate arm of the immune system also has a range of inhibitory receptors that can counteract activating signals and suppress the effector immune responses. Targeting these innate inhibitory receptors may provide a complementary therapeutic approach in several immune-related conditions, including transplantation. In this review, we will explore the potential role of innate inhibitory receptors in controlling alloimmunity during solid organ transplantation.

A novel mechanism of cannabidiol in suppressing ovarian cancer through LAIR-1 mediated mitochondrial dysfunction and apoptosis

Cannabidiol (CBD) is a nonpsychoactive cannabinoid compound. It has been shown that CBD can inhibit the proliferation of ovarian cancer cells, but the underlying specific mechanism is unclear. We previously presented the first evidence for the expression of leukocyte-associated immunoglobulin-like receptor 1 (LAIR-1), a member of the immunosuppressive receptor family, in ovarian cancer cells. In the present study, we investigated the mechanism by which CBD inhibits the growth of SKOV3 and CAOV3 ovarian cancer cells, and we sought to understand the concurrent role of LAIR-1. In addition to inducing ovarian cancer cell cycle arrest and promoting cell apoptosis, CBD treatment significantly affected the expression of LAIR-1 and inhibited the PI3K/AKT/mTOR signaling axis and mitochondrial respiration in ovarian cancer cells. These changes were accompanied by an increase in ROS, loss of mitochondrial membrane potential, and suppression of mitochondrial respiration and aerobic glycolysis, thereby inducing abnormal or disturbed metabolism and reducing ATP production. A combined treatment with N-acetyl-l-cysteine and CBD indicated that a reduction in ROS production would restore PI3K/AKT/mTOR pathway signaling and ovarian cancer cell proliferation. We subsequently confirmed that the inhibitory effect of CBD on the PI3K/AKT/mTOR signal axis and mitochondrial bioenergy metabolism was attenuated by knockdown of LAIR-1. Our animal studies further support the in vivo anti-tumor activity of CBD and suggest its mechanism of action. In summary, the present findings confirm that CBD inhibits ovarian cancer cell growth by disrupting the LAIR-1-mediated interference with mitochondrial bioenergy metabolism and the PI3K/AKT/mTOR pathway. These results provide a new experimental basis for research into ovarian cancer treatment based on targeting LAIR-1 with CBD.

LAIR1, an ITIM-Containing Receptor Involved in Immune Disorders and in Hematological Neoplasms

Leukocyte-associated immunoglobulin (Ig)-like receptor 1 (LAIR1, CD305) belongs to the family of immune-inhibitory receptors and is widely expressed on hematopoietic mature cells, particularly on immune cells. Four different types of ligands of LAIR1 have been described, including collagens, suggesting a potential immune-regulatory function on the extracellular matrix. By modulating cytokine secretion and cellular functions, LAIR1 displays distinct patterns of expression among NK cell and T/B lymphocyte subsets during their differentiation and cellular activation and plays a major negative immunoregulatory role. Beyond its implications in physiology, the activity of LAIR1 can be inappropriately involved in various autoimmune or inflammatory disorders and has been implicated in cancer physiopathology, including hematological neoplasms. Its action as an inhibitory receptor can result in the dysregulation of immune cellular responses and in immune escape within the tumor microenvironment. Furthermore, when expressed by tumor cells, LAIR1 can modulate their proliferation or invasion properties, with contradictory pro- or anti-tumoral effects depending on tumor type. In this review, we will focus on its role in normal physiological conditions, as well as during pathological situations, including hematological malignancies. We will also discuss potential therapeutic strategies targeting LAIR1 for the treatment of various autoimmune diseases and cancer settings.

Differential isoform expression of Allergin-1 during acute and chronic inflammation

INTRODUCTION

Neutrophils are crucial to antimicrobial defense, but excessive neutrophilic inflammation elicits immune pathology. Currently, no effective treatment exists to curb neutrophil activation. However, neutrophils express a variety of inhibitory receptors which may represent potential therapeutic targets to limit neutrophilic inflammation. Indeed, we previously showed that the inhibitory collagen receptor leukocyte-associated immunoglobulin-like receptor 1 (LAIR-1) regulates neutrophilic airway inflammation and inhibits neutrophil extracellular trap formation. The inhibitory receptor Allergin-1 is expressed by myeloid cells and B cells. Allergin-1 suppresses mast cell and basophil activation, but a potential regulatory role on neutrophils remains unexplored. We aimed to demonstrate the regulation of neutrophils by Allergin-1.

METHODS

We examine Allergin-1 isoform expression on human neutrophils during homeostatic (healthy donors) and chronic inflammatory (systemic lupus erythematosus patients) conditions in comparison to other circulating leukocytes by flow cytometry. To reveal a potential role for Allergin-1 in regulating neutrophilic inflammation, we experimentally infect wild-type (WT) and Allergin-1-deficient mice with a respiratory syncytial virus (RSV) and monitor disease severity and examine cellular airway infiltrate. Flow cytometry was used to confirm Allergin-1 expression by airway-infiltrated neutrophils in RSV infection-induced bronchiolitis patients.

RESULTS

Only the short 1 (S1) isoform, but not the long (L) or S2 isoform could be detected on blood leukocytes, with the exception of nonclassical monocytes, which exclusively express the S2 isoform. Allergin-1 expression levels did not vary significantly between healthy individuals and patients with the systemic inflammatory disease on any interrogated cell type. Airway-infiltrated neutrophils of pediatric RSV bronchiolitis patients were found to express Allergin-1S1. However, Allergin-1-deficient mice experimentally infected with RSV did not show exacerbated disease or increased neutrophil airway infiltration compared to WT littermates.

CONCLUSION

Allergin-1 isoform expression is unaffected by chronic inflammatory conditions. In stark contrast to fellow inhibitory receptor LAIR-1, Allergin-1 does not regulate neutrophilic inflammation in a mouse model of RSV bronchiolitis.

Understanding inhibitory receptor function in neutrophils through the lens of CLEC12A

Neutrophils are the first leukocytes recruited from the circulation in response to invading pathogens or injured cells. To eradicate pathogens and contribute to tissue repair, recruited neutrophils generate and release a host of toxic chemicals that can also damage normal cells. To avoid collateral damage leading to tissue injury and organ dysfunction, molecular mechanisms evolved that tightly control neutrophil response threshold to activating signals, the strength and location of the response, and the timing of response termination. One mechanism of response control is interruption of activating intracellular signaling pathways by the 20 inhibitory receptors expressed by neutrophils. The two inhibitory C-type lectin receptors expressed by neutrophils, CLEC12A and DCIR, exhibit both common and distinct molecular and functional mechanisms, and they are associated with different diseases. In this review, we use studies on CLEC12A as a model of inhibitory receptor regulation of neutrophil function and participation in disease. Understanding the molecular mechanisms leading to inhibitory receptor specificity offers the possibility of using physiologic control of neutrophil functions as a pharmacologic tool to control inflammatory diseases.

Deficiency of C-reactive protein or human C-reactive protein transgenic treatment aggravates influenza A infection in mice

C-reactive protein (CRP) has been shown to be a potential candidate target in the immunotherapy of severe influenza A infection. However, it is unclear on the pathogenesis associated with CRP in influenza infections. Here, we used influenza A H1N1 CA04 to infect human CRP transgenic mice (KI), CRP knockout mice (KO), and wild-type mice (WT), respectively, and compared the viral pathogenicity and associated immune response in those mice. The results showed that CA04 infection resulted in 100%, 80%, and 60% death in KO, KI, and WT mice, respectively. Compared to WT mice, CA04 infection resulted in higher TCID50 in lungs on day 3 after infection but lowered HI antibody titers in sera of survivors on day 21 after infection in KI mice. ELISA assay showed that IFN-γ concentration was significantly increased in sera of WT, KI, or KO mice on day 7 after infection, and IL-17 was remarkably increased in sera of WT mice but decreased in sera of KI mice while no significant change in sera of KO mice on day 3 or 7 after infection. Quantitative RT-PCR showed that the relative expression levels of immune checkpoint CTLA-4, LAIR-1, GITR, BTLA, TIM-3, or PD-1 mRNA in the lung presented decreased levels on day 3 or 7 after infection in KI or KO mice. The correlation analysis showed that mRNA expression levels of the 6 molecules positively correlated with viral TICD50 in WT mice but negatively correlated with viral TCID50 in KI or KO mice. However, only LAIR-1 presented a significant correlation in each lung tissue of WT, KI, or KO mice with CA07 infection statistically. IHC results showed that LAIR-1 positive cells could be found in WT, KO, or KI mice lung tissues with CA04 infection, and the positive cells were mainly distributed in an inflammatory dense area. Our results suggested that deficiency of CRP or human CRP transgenic treatment aggravates influenza A virus infection in mice. CRP is a double sword in immune regulation of influenza infection in which IL-17 and immune checkpoint may be involved.

Extracellular matrix-natural killer cell interactome: an uncharted territory in health and disease

Extracellular matrix (ECM) constantly undergoes remodeling to maintain the tissue homeostasis and an impaired ECM remodeling is a hallmark of many diseases, including cancer, infections, and inflammatory disorders. ECM has recently become recognized to regulate the immune response in peripheral tissues. Most immune cells express a diverse array of ECM receptors that, upon engagement by their cognate ECM ligands, can regulate their movement and effector functions. Natural killer (NK) cells are innate lymphocytes capable of mounting a swift cytotoxic immunity against cancer and virally infected cells using germline-encoded activating and inhibitory receptors. Regulation of NK cell effector function by ECM proteins in peripheral tissues is an emerging field with major implications for maintaining tolerance in normal tissues and controlling solid cancers, viral infections, and inflammatory diseases. The development of novel therapeutics targeting ECM-NK cell interplay represents a promising strategy to promote health and combat many diseases affecting solid organs.

Anti-inflammatory effects of curcumin-loaded niosomes on respiratory syncytial virus infection in a mice model

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract infection in paediatrics. While antivirals are apparent candidates to treat RSV-induced diseases, they have not yet met expectations and have remained in infancy. There is growing evidence to suggest that modulating the exacerbated inflammation during RSV infection can improve disease outcome. Curcumin-loaded niosomes have anti-inflammatory effects against RSV-induced respiratory disease by reducing immune cells' infiltration and inflammatory cytokines' production. This study evaluated the effects of curcumin-loaded niosomes on RSV-induced immunopathology in a mice model. Curcumin-loaded niosomes were prepared using the thin-film hydration method and characterized in vitro. Female Balb/c mice were infected by RSV-A2 and treated daily with curcumin-loaded niosomes. The potential anti-inflammatory effects of curcumin-loaded niosomes were evaluated on day 5 after infection. Using curcumin-loaded niosomes decreased immune cell influx and the inflammatory mediators (MIP-1α, TNF-α and IFN-γ) production in the lung, resulting in alleviated lung pathology following RSV infection. These findings indicate that curcumin-loaded niosomes have anti-inflammatory potential and could be a promising candidate to alleviate RSV-associated immunopathology.

Inhibitory pattern recognition receptors

Pathogen- and damage-associated molecular patterns are sensed by the immune system's pattern recognition receptors (PRRs) upon contact with a microbe or damaged tissue. In situations such as contact with commensals or during physiological cell death, the immune system should not respond to these patterns. Hence, immune responses need to be context dependent, but it is not clear how context for molecular pattern recognition is provided. We discuss inhibitory receptors as potential counterparts to activating pattern recognition receptors. We propose a group of inhibitory pattern recognition receptors (iPRRs) that recognize endogenous and microbial patterns associated with danger, homeostasis, or both. We propose that recognition of molecular patterns by iPRRs provides context, helps mediate tolerance to microbes, and helps balance responses to danger signals.

LAIR-1 acts as an immune checkpoint on activated ILC2s and regulates the induction of airway hyperreactivity

BACKGROUND

Type 2 innate lymphoid cells (ILC2s) are relevant players in type 2 asthma. They initiate eosinophil infiltration and airway hyperreactivity (AHR) through cytokine secretion. Leukocyte-associated immunoglobulin-like receptor 1 (LAIR-1) is an inhibitory receptor considered to be an immune checkpoint in different inflammatory diseases.

OBJECTIVE

Our aim here was to investigate the expression of LAIR-1 and assess its role in human and murine ILC2s.

METHODS

Wild-type and LAIR-1 knockout mice were intranasally challenged with IL-33, and pulmonary ILC2s were sorted to perform an ex vivo comparative study based on RNA sequencing and flow cytometry. We next studied the impact of LAIR-1 deficiency on AHR and lung inflammation by using knockout mice and adoptive transfer experiments in Rag2-/-Il2rg-/- mice. Knockdown antisense strategies and humanized mice were used to assess the role of LAIR-1 in human ILC2s.

RESULTS

We have demonstrated that LAIR-1 is inducible on activated ILC2s and downregulates cytokine secretion and effector function. LAIR-1 signaling in ILC2s was mediated via inhibitory pathways, including SHP1/PI3K/AKT, and LAIR-1 deficiency led to exacerbated ILC2-dependent AHR in IL-33 and Alternaria alternata models. In adoptive transfer experiments, we confirmed the LAIR-1-mediated regulation of ILC2s in vivo. Interestingly, LAIR-1 was expressed and inducible in human ILC2s, and knockdown approaches of Lair1 resulted in higher cytokine production. Finally, engagement of LAIR-1 by physiologic ligand C1q significantly reduced ILC2-dependent AHR in a humanized ILC2 murine model.

CONCLUSION

Our results unravel a novel regulatory axis in ILC2s with the capacity to reduce allergic AHR and lung inflammation.

Neuroinflammatory gene expression in chronic prostatitis/chronic pelvic pain syndrome patients: insights into etiology and phenotype biology

Background

Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) has diverse clinical phenotypes and its etiology is multifactorial. Studies to date of gene expression in humans have been limited to small numbers of target genes. NanoString can simultaneously measure hundreds of genes. We wished to study gene expression in blood and urine of CP/CPPS patients compared to controls for neuroinflammatory genes and characterize the results by patient phenotype.

Methods

Blood and urine were collected from 10 men with CP/CPPS and 7 asymptomatic controls. RNA was isolated from urine pellets using Qiagen RNeasy kits. Whole blood was collected and RNA isolated. 100 ng of RNA was used for gene expression analysis with the 770-gene NanoString Human Neuroinflammation gene panel. Data was imported into Rosalind (OnRamp Bioinformatics) for normalization, calculation of fold-changes and P values, and identification of enriched pathways. Gene expression was considered significantly different if there was a greater than 1.5× change compared to controls and corrected P was <0.05.

Results

Mean patient age was 42.2 years, median symptom duration was 15.5 months, median UPOINT domains was 3 and mean total National Institute of Health-Chronic Prostatitis Symptom Index Score was 28.8. In blood, there were 5 genes with significantly different expression to controls, the largest differences found in FOS1 (neuropathic pain control), PROS1 (blood clotting) and DDX58 (antiviral innate immunity). Gene set analysis showed differences in inflammation, angiogenesis and cytokine signaling. In urine there were 48 genes with significantly different expression including SLAMF8 (lymphocyte activation) and LAIR1 (inhibits B and T cell function). Gene set analysis showed differences in carbohydrate metabolism, neurons and neurotransmission, adaptive immunity and inflammatory signaling. Subgroup analysis by UPOINT domain showed unique gene expression in the Organ Specific and Neurologic/Systemic domains in both blood and urine for neurogenic pain and cytokine signaling associated genes

Conclusions

Men with CP/CPPS have a diverse set of neuroinflammatory genes with differential expression compared to controls. Clinical phenotypes have distinct patterns of gene expression. These findings could lead to novel biomarker development, emphasize the importance of multimodal therapy targeting diverse pathways and further validate the biologic basic of clinical phenotyping.

Blood neutrophils from children with COVID-19 exhibit both inflammatory and anti-inflammatory markers

Background

Perhaps reflecting that children with COVID-19 rarely exhibit severe respiratory symptoms and often remain asymptomatic, little attention has been paid to explore the immune response in pediatric COVID-19. Here, we analyzed the phenotype and function of circulating neutrophils from children with COVID-19.

Methods

An observational study including 182 children with COVID-19, 21 children with multisystem inflammatory syndrome (MIS-C), and 40 healthy children was performed in Buenos Aires, Argentina. Neutrophil phenotype was analyzed by flow cytometry in blood samples. Cytokine production, plasma levels of IgG antibodies directed to the spike protein of SARS-CoV-2 and citrullinated histone H3 were measured by ELISA. Cell-free DNA was quantified by fluorometry.

Findings

Compared with healthy controls, neutrophils from children with COVID-19 showed a lower expression of CD11b, CD66b, and L-selectin but a higher expression of the activation markers HLA-DR, CD64 and PECAM-1 and the inhibitory receptors LAIR-1 and PD-L1. No differences in the production of cytokines and NETs were observed. Interestingly, the expression of CD64 in neutrophils and the serum concentration of IgG antibodies directed to the spike protein of SARS-CoV-2 distinguished asymptomatic from mild and moderate COVID-19.

Interpretation

Acute lung injury is a prominent feature of severe COVID-19 in adults. A low expression of adhesion molecules together with a high expression of inhibitory receptors in neutrophils from children with COVID-19 might prevent tissue infiltration by neutrophils preserving lung function.

SUL-151 Decreases Airway Neutrophilia as a Prophylactic and Therapeutic Treatment in Mice after Cigarette Smoke Exposure

Chronic obstructive pulmonary disease (COPD) caused by cigarette smoke (CS) is featured by oxidative stress and chronic inflammation. Due to the poor efficacy of standard glucocorticoid therapy, new treatments are required. Here, we investigated whether the novel compound SUL-151 with mitoprotective properties can be used as a prophylactic and therapeutic treatment in a murine CS-induced inflammation model. SUL-151 (4 mg/kg), budesonide (500 μg/kg), or vehicle were administered via oropharyngeal instillation in this prophylactic and therapeutic treatment setting. The number of immune cells was determined in the bronchoalveolar lavage fluid (BALF). Oxidative stress response, mitochondrial adenosine triphosphate (ATP) production, and mitophagy-related proteins were measured in lung homogenates. SUL-151 significantly decreased more than 70% and 50% of CS-induced neutrophils in BALF after prophylactic and therapeutic administration, while budesonide showed no significant reduction in neutrophils. Moreover, SUL-151 prevented the CS-induced decrease in ATP and mitochondrial mtDNA and an increase in putative protein kinase 1 expression in the lung homogenates. The concentration of SUL-151 was significantly correlated with malondialdehyde level and radical scavenging activity in the lungs. SUL-151 inhibited the increased pulmonary inflammation and mitochondrial dysfunction in this CS-induced inflammation model, which implied that SUL-151 might be a promising candidate for COPD treatment.

Nutritional immunity: the impact of metals on lung immune cells and the airway microbiome during chronic respiratory disease

Nutritional immunity is the sequestration of bioavailable trace metals such as iron, zinc and copper by the host to limit pathogenicity by invading microorganisms. As one of the most conserved activities of the innate immune system, limiting the availability of free trace metals by cells of the immune system serves not only to conceal these vital nutrients from invading bacteria but also operates to tightly regulate host immune cell responses and function. In the setting of chronic lung disease, the regulation of trace metals by the host is often disrupted, leading to the altered availability of these nutrients to commensal and invading opportunistic pathogenic microbes. Similarly, alterations in the uptake, secretion, turnover and redox activity of these vitally important metals has significant repercussions for immune cell function including the response to and resolution of infection. This review will discuss the intricate role of nutritional immunity in host immune cells of the lung and how changes in this fundamental process as a result of chronic lung disease may alter the airway microbiome, disease progression and the response to infection.

Neutrophils in respiratory syncytial virus infection: From harmful effects to therapeutic opportunities

Respiratory syncytial virus (RSV) is an important infectious agent in infants and young children. In most cases, RSV infection only causes mild disease, but in some, it requires invasive ventilation. Although antiviral drugs are obvious candidates to treat viral illness, and some have shown antiviral effects in humans, antivirals such as GS-5806, ALX-0171 and ALS-8176 have not yet met their expectations. Since the inappropriate or dysregulated immune response against RSV leads to harmful immune pathology, a robust immune cascade is probably underway by the time patients reach the hospital. RSV infection is associated with a strong neutrophil influx into the airway. It not clear if these cells contribute to antiviral defence or to lung pathology. This article discusses the protective and harmful roles of neutrophils during RSV infection and provides an overview of mechanisms by which neutrophil function could be targeted to prevent tissue injury and preserve homeostasis.

Immunoregulatory complement receptor-1 and leukocyte-associated Ig-like receptor-1 expression on leukocytes in Psoriasis vulgaris

Psoriasis vulgaris (PsV) is an immune-mediated inflammatory disorder with devastating psychosocial consequences. Expression of immunoregulator molecules on leukocytes in PsV remains unclear. Leukocyte-associated Ig-like receptor-1 (LAIR-1) and complement receptor-1 (CR-1) are immunoregulator receptors reported to bind complement component 1q involved in phagocytosis. We aimed to explore if altered leukocyte expression of LAIR-1 and CR-1 is associated with PsV. This case-control study included 36 PsV patients and 36 healthy controls. Neutrophils, monocytes and B and T cells were examined by flow cytometry for LAIR-1 and CR-1 mean fluorescence intensity (MFI) and positive cell percentage. Comparison between both groups revealed a significant decrease in LAIR-1 MFI on neutrophils and T cells (P < 0.001 and P = 0.003, respectively). CR-1 MFI on neutrophils, monocytes and T cells also showed a significant decrease in patients (P = 0.033, P = 0.001 and P = 0.040, respectively). There was a significant positive correlation of LAIR-1 MFI on neutrophils with CR-1 MFI on neutrophils (r = 0.503; P = 0.002) and LAIR-1 MFI on monocytes with CR-1 MFI on monocytes (r = 0.371; P = 0.026). Receiver operating characteristic curves revealed that CR-1 MFI on monocytes had the highest discrimination power to differentiate patients from controls, with 86.1% specificity and 75% sensitivity (P = 0.001). In conclusion, altered leukocytes expression of LAIR-1 and CR-1 is associated with PsV. Down-regulated CR-1 MFI on monocytes is a promising diagnostic biomarker for PsV.

Transcriptome of airway neutrophils reveals an interferon response in life-threatening respiratory syncytial virus infection

BACKGROUND

Neutrophils are the most abundant cell type infiltrating the airways during severe respiratory syncytial virus (RSV) infection. Their exact role in disease pathophysiology remains enigmatic. Therefore, we determined genome-wide RNA expression profiles of local and systemic neutrophils in RSV bronchiolitis to provide further insight into local neutrophil biology.

METHODS

We performed a single-center analysis, in 16 infants, admitted to the pediatric intensive care unit with severe RSV bronchiolitis. Neutrophils were isolated from blood and tracheobronchial aspirates (sputum). After low input RNA sequencing, differential expression of genes was determined followed by gene set analysis.

RESULTS

Paired transcriptomic analysis of airway versus blood neutrophils showed an inflammatory phenotype, characterized by NF-kB signaling and upregulated expression of IL-6 and interferon pathways. We observed distinct expression of neutrophil activation genes (TNFSF13B, FCER1G).

DISCUSSION

Our data indicate that airway neutrophils regulate their function at the transcriptional level in response to viral infection. It also suggests that local interferon drives the neutrophil response of severe RSV bronchiolitis.

Leukocyte Associated Immunoglobulin Like Receptor 1 Regulation and Function on Monocytes and Dendritic Cells During Inflammation

Inhibitory receptors are crucial immune regulators and are essential to prevent exacerbated responses, thus contributing to immune homeostasis. Leukocyte associated immunoglobulin like receptor 1 (LAIR-1) is an immune inhibitory receptor which has collagen and collagen domain containing proteins as ligands. LAIR-1 is broadly expressed on immune cells and has a large availability of ligands in both circulation and tissues, implicating a need for tight regulation of this interaction. In the current study, we sought to examine the regulation and function of LAIR-1 on monocyte, dendritic cell (DC) and macrophage subtypes, using different in vitro models. We found that LAIR-1 is highly expressed on intermediate monocytes as well as on plasmacytoid DCs. LAIR-1 is also expressed on skin immune cells, mainly on tissue CD14⁺ cells, macrophages and CD1c⁺ DCs. In vitro, monocyte and type-2 conventional DC stimulation leads to LAIR-1 upregulation, which may reflect the importance of LAIR-1 as negative regulator under inflammatory conditions. Indeed, we demonstrate that LAIR-1 ligation on monocytes inhibits toll like receptor (TLR)4 and Interferon (IFN)-α- induced signals. Furthermore, LAIR-1 is downregulated on GM-CSF and IFN-γ monocyte-derived macrophages and monocyte-derived DCs. In addition, LAIR-1 triggering during monocyte derived-DC differentiation results in significant phenotypic changes, as well as a different response to TLR4 and IFN-α stimulation. This indicates a role for LAIR-1 in skewing DC function, which impacts the cytokine expression profile of these cells. In conclusion, we demonstrate that LAIR-1 is consistently upregulated on monocytes and DC during the inflammatory phase of the immune response and tends to restore its expression during the resolution phase. Under inflammatory conditions, LAIR-1 has an inhibitory function, pointing toward to a potential intervention opportunity targeting LAIR-1 in inflammatory conditions.

Cellular uptake of collagens and implications for immune cell regulation in disease

As the dominant constituent of the extracellular matrix (ECM), collagens of different types are critical for the structural properties of tissues and make up scaffolds for cellular adhesion and migration. Importantly, collagens also directly modulate the phenotypic state of cells by transmitting signals that influence proliferation, differentiation, polarization, survival, and more, to cells of mesenchymal, epithelial, or endothelial origin. Recently, the potential of collagens to provide immune regulatory signals has also been demonstrated, and it is believed that pathological changes in the ECM shape immune cell phenotype. Collagens are themselves heavily regulated by a multitude of structural modulations or by catabolic pathways. One of these pathways involves a cellular uptake of collagens or soluble collagen-like defense collagens of the innate immune system mediated by endocytic collagen receptors. This cellular uptake is followed by the degradation of collagens in lysosomes. The potential of this pathway to regulate collagens in pathological conditions is evident from the increased extracellular accumulation of both collagens and collagen-like defense collagens following endocytic collagen receptor ablation. Here, we review how endocytic collagen receptors regulate collagen turnover during physiological conditions and in pathological conditions, such as fibrosis and cancer. Furthermore, we highlight the potential of collagens to regulate immune cells and discuss how endocytic collagen receptors can directly regulate immune cell activity in pathological conditions or do it indirectly by altering the extracellular milieu. Finally, we discuss the potential collagen receptors utilized by immune cells to directly detect ECM-related changes in the tissues which they encounter.

The Contribution of Neutrophils to the Pathogenesis of RSV Bronchiolitis

Acute viral bronchiolitis causes significant mortality in the developing world, is the number one cause of infant hospitalisation in the developed world, and is associated with the later development of chronic lung diseases such as asthma. A vaccine against respiratory syncytial virus (RSV), the leading cause of viral bronchiolitis in infancy, remains elusive, and hence new therapeutic modalities are needed to limit disease severity. However, much remains unknown about the underlying pathogenic mechanisms. Neutrophilic inflammation is the predominant phenotype observed in infants with both mild and severe disease, however, a clear understanding of the beneficial and deleterious effects of neutrophils is lacking. In this review, we describe the multifaceted roles of neutrophils in host defence and antiviral immunity, consider their contribution to bronchiolitis pathogenesis, and discuss whether new approaches that target neutrophil effector functions will be suitable for treating severe RSV bronchiolitis.

Cancer immunotherapy based on blocking immune suppression mediated by an immune modulator LAIR-1

The leukocyte-associated immunoglobulin-like receptor 1 (LAIR-1) is an inhibitory receptor expressed on the majority of peripheral blood mononuclear cells and is important for the regulation of immune responses. The binding of LAIR-1 to its ligands results in the loss of immune function in the tumor microenvironment (TME) and a reduction in T cell function and immune responses of antigen-presenting cells. Using bioinformatics analysis, we showed that LAIR-1 is broadly upregulated in multiple types of cancer. By designing a LAIR-2-Fc recombinant protein to block the binding of LAIR-1 to its ligand collagen, we observed augmented cytotoxic T cell infiltration and function resulting in antitumor immune responses that eliminated cancer cells. Besides, LAIR-2-Fc fusion protein potentiated the antitumor effect of PD-1/L1 checkpoint blockade therapy. Collectively, our results support the targeting of LAIR-1 for potential immunotherapeutic applications.

Neutrophil Adaptations upon Recruitment to the Lung: New Concepts and Implications for Homeostasis and Disease

Neutrophils have a prominent role in all human immune responses against any type of pathogen or stimulus. The lungs are a major neutrophil reservoir and neutrophilic inflammation is a primary response to both infectious and non-infectious challenges. While neutrophils are well known for their essential role in clearance of bacteria, they are also equipped with specific mechanisms to counter viruses and fungi. When these defense mechanisms become aberrantly activated in the absence of infection, this commonly results in debilitating chronic lung inflammation. Clearance of bacteria by phagocytosis is the hallmark role of neutrophils and has been studied extensively. New studies on neutrophil biology have revealed that this leukocyte subset is highly adaptable and fulfills diverse roles. Of special interest is how these adaptations can impact the outcome of an immune response in the lungs due to their potent capacity for clearing infection and causing damage to host tissue. The adaptability of neutrophils and their propensity to influence the outcome of immune responses implicates them as a much-needed target of future immunomodulatory therapies. This review highlights the recent advances elucidating the mechanisms of neutrophilic inflammation, with a focus on the lung environment due to the immense and growing public health burden of chronic lung diseases such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD), and acute lung inflammatory diseases such as transfusion-related acute lung injury (TRALI).