Galectin-9 Is a Possible Promoter of Immunopathology in Rheumatoid Arthritis by Activation of Peptidyl Arginine Deiminase 4 (PAD-4) in Granulocytes

Galectin-9 as an indicator of functional limitations and radiographic joint damage in patients with rheumatoid arthritis

Background

Previous studies have revealed that Galectin-9 (Gal-9) acts as an apoptosis modulator in autoimmunity and rheumatic inflammation. In the present study, we investigated the potential role of Gal-9 as a biomarker in patients with rheumatoid arthritis (RA), especially as an indicator of functional limitations and radiographic joint damage.

Methods

A total of 146 patients with RA and 52 age- and sex-matched healthy controls were included in this study. Clinical data including disease activity, physical function, and radiographic joint damage were assessed. Functional limitation was defined as the Stanford Health Assessment Questionnaire (HAQ) disability index >1. Subjects with joint erosion >0 or joint space narrowing >0 were considered to have radiographic joint damage. Serum Gal-9 levels were detected by an enzyme-linked immunosorbent assay. Univariate and multivariate logistic regression analysis were used to evaluate the association between Gal-9 and high disease activity and functional limitations, and a prediction model was established to construct predictive nomograms.

Results

Serum levels of Gal-9 were significantly increased in patients with RA compared to those in healthy controls (median 13.1 ng/mL vs. 7.6 ng/mL). Patients with RA who were older (>65 years), had a longer disease duration (>5 years), longer morning stiffness (>60mins), elevated serum erythrocyte sedimentation rate and C-reactive protein, and difficult-to-treat RA had significantly higher Gal-9 levels than those in the corresponding control subgroups (all p <0.05). Patients with RA were divided into two subgroups according to the cut-off value of Gal-9 of 11.6 ng/mL. Patients with RA with Gal-9 >11.6 ng/mL had a significantly higher core clinical disease activity index, HAQ scores, Sharp/van der Heijde modified Sharp scores, as well as a higher percentage of advanced joint damage (all p<0.05) than patients with Gal-9 ≤11.6 ng/mL. Accordingly, patients with RA presenting either functional limitations or radiographic joint damage had significantly higher serum Gal-9 levels than those without (both p <0.05). Furthermore, multivariate logistic regression analysis showed that a serum level of Gal-9 >11.6 ng/mL was an independent risk factor for high disease activity (OR=3.138, 95% CI 1.150-8.567, p=0.026) and presence of functional limitations (OR=2.455, 95% CI 1.017-5.926, p=0.046), respectively.

Conclusion

Gal-9 could be considered as a potential indicator in patients with RA, especially with respect to functional limitations and joint damage.

Targeting Neutrophil Extracellular Traps in Gouty Arthritis: Insights into Pathogenesis and Therapeutic Potential

Gouty arthritis (GA) is an immune-mediated disorder characterized by severe inflammation due to the deposition of monosodium urate (MSU) crystals in the joints. The pathophysiological mechanisms of GA are not yet fully understood, and therefore, the identification of effective therapeutic targets is of paramount importance. Neutrophil extracellular traps (NETs), an intricate structure of DNA scaffold, encompassing myeloperoxidase, histones, and elastases - have gained significant attention as a prospective therapeutic target for gouty arthritis, due to their innate antimicrobial and immunomodulatory properties. Hence, exploring the therapeutic potential of NETs in gouty arthritis remains an enticing avenue for further investigation. During the process of gouty arthritis, the formation of NETs triggers the release of inflammatory cytokines, thereby contributing to the inflammatory response, while MSU crystals and cytokines are sequestered and degraded by the aggregation of NETs. Here, we provide a concise summary of the inflammatory processes underlying the initiation and resolution of gouty arthritis mediated by NETs. Furthermore, this review presents an overview of the current pharmacological approaches for treating gouty arthritis and summarizes the potential of natural and synthetic product-based inhibitors that target NET formation as novel therapeutic options, alongside elucidating the intrinsic challenges of these inhibitors in NETs research. Lastly, the limitations of HL-60 cell as a suitable substitute of neutrophils in NETs research are summarized and discussed. Series of recommendations are provided, strategically oriented towards guiding future investigations to effectively address these concerns. These findings will contribute to an enhanced comprehension of the interplay between NETs and GA, facilitating the proposition of innovative therapeutic strategies and novel approaches for the management of GA.

Knockdown of Galectin-9 alleviates rheumatoid arthritis through suppressing TNF-α-induced activation of fibroblast-like synoviocytes

The role of Galectin-9 (Gal-9) in the pathogenesis of rheumatoid arthritis (RA) remains unclear. This study aimed to investigate the mechanism of action and therapeutic potential of Gal-9 in RA. We detected Gal-9 expression in clinical samples, explored the mechanism of function of Gal-9 by knockdown and overexpression in fibroblast-like synoviocytes (FLSs), and further verified it in collagen-induced arthritis (CIA) model. We found that the levels of Gal-9 were considerably elevated in RA synovium than in osteoarthritis (OA) patients. A substantial decrease of Gal-9 was demonstrated after tumor necrosis factor (TNF-α) inhibitor treatment in the plasma of patients with RA. Additionally, transcriptome sequencing revealed that Gal-9 was involved in the regulation of the TNF-α pathway. Gal-9 was considerably upregulated after TNF-α stimulation in FLSs, and knockdown of Gal-9 substantially inhibited TNF-α activated proliferation, migration and inflammatory response. According to cell transcriptome sequencing results, we further confirmed that Gal-9 could achieve these effects by interacting with MAFB and affecting PI3K/AKT/mTOR pathway. Finally, we knocked down Gal-9 on the CIA model and found that it could alleviate the progression of arthritis. In conclusion, our study revealed that the knockdown of Gal-9 could inhibited TNF-α induced activation in RA through MAFB, PI3K/AKT/mTOR.

Peptidyl Arginine Deiminases in Chronic Diseases: A Focus on Rheumatoid Arthritis and Interstitial Lung Disease

Protein citrullination is accomplished by a broad enzyme family named Peptidyl Arginine Deiminases (PADs), which makes this post-translational modification in many proteins that perform physiological and pathologic mechanisms in the body. Due to these modifications, citrullination has become a significant topic in the study of pathological processes. It has been related to some chronic and autoimmune diseases, including rheumatoid arthritis (RA), interstitial lung diseases (ILD), multiple sclerosis (MS), and certain types of cancer, among others. Antibody production against different targets, including filaggrin, vimentin, and collagen, results in an immune response if they are citrullinated, which triggers a continuous inflammatory process characteristic of autoimmune and certain chronic diseases. PAD coding genes (PADI1 to PADI4 and PADI6) harbor variations that can be important in these enzymes' folding, activity, function, and half-life. However, few studies have considered these genetic factors in the context of chronic diseases. Exploring PAD pathways and their role in autoimmune and chronic diseases is a major topic in developing new pharmacological targets and valuable biomarkers to improve diagnosis and prevention. The present review addresses and highlights genetic, molecular, biochemical, and physiopathological factors where PAD enzymes perform a major role in autoimmune and chronic diseases.

Advancing Treatment in Bullous Pemphigoid: A Comprehensive Review of Novel Therapeutic Targets and Approaches

Bullous pemphigoid is one of the most common autoimmune bullous diseases occurring primarily in the elderly. Pathogenic autoantibodies against BP180 and BP230 at the dermal-epidermal junction cause subepidermal blisters, erosions, and intense pruritus, all of which adversely affect the patients' quality of life and may increase their morbidity and mortality. Current systemic treatment options for bullous pemphigoid are limited to corticosteroids and immunosuppressants, which can have substantial side effects on these vulnerable patients that even exceed their therapeutic benefits. Therefore, more precisely, targeting therapies to the pathogenic cells and molecules in bullous pemphigoid is an urgent issue. In this review, we describe the pathophysiology of bullous pemphigoid, focusing on autoantibodies, complements, eosinophils, neutrophils, proteases, and the T helper 2 and 17 axes since they are crucial in promoting proinflammatory environments. We also highlight the emerging therapeutic targets for bullous pemphigoid and their latest discoveries in clinical trials or experimental studies. Further well-designed studies are required to establish the efficacy and safety of these prospective therapeutic options.

A study of the association between Galectin-9 gene (LGALS9) polymorphisms and rheumatoid arthritis in Egyptian patients

Background

Rheumatoid arthritis (RA) is an incessant synovial inflammation of an autoimmune origin, destroying articular cartilages and bones. Galectins are an evolutionarily conserved family of immune-modulatory animal lectins detected in a number of immune cells like T cells, fibroblasts and macrophages. Galectin 9 (Gal-9) has been the subject of many studies for being linked to regulation of both innate and adaptive immune reactions. The objective of the study was to evaluate the link between the Galectin-9 gene (LGALS9) polymorphisms and the susceptibility of RA in Egyptian patients, as well as, detection of the serum level of Gal-9 in RA and its association with LGALS9 polymorphisms, the activity of RA and radiological damage.

Methods

A study of 85 participants; group (I): 60 RA cases and group (II): 25 apparently healthy subjects. RA Disease activity index (DAS-28) and Larsen index score were assessed. LGALS9 gene and serum Gal-9 were investigated.

Results

rs4239242 TT genotype and T allele occurred more frequently in RA cases than controls with a significant difference (P = 0.006; P < 0.001 respectively). Gal-9 level was significantly higher among RA cases than control group (P = 0.017). The Gal-9 level showed negative significant correlations with DAS-28 and Larsen score (P < 0.001).

Conclusion

RA is strongly linked to genetic alterations in the LGALS9 gene and the single nucleotide polymorphism (SNP) rs4239242 TT genotype in the Egyptian population. RA cases in remission or those with low disease activity had higher levels of serum Gal-9 in comparison to cases with moderate and high disease activity and this would be promising in the future of RA treatment.

Galectin-9 has non-apoptotic cytotoxic activity toward acute myeloid leukemia independent of cytarabine resistance

Acute myeloid leukemia (AML) is a malignancy still associated with poor survival rates, among others, due to frequent occurrence of therapy-resistant relapse after standard-of-care treatment with cytarabine (AraC). AraC triggers apoptotic cell death, a type of cell death to which AML cells often become resistant. Therefore, therapeutic options that trigger an alternate type of cell death are of particular interest. We previously identified that the glycan-binding protein Galectin-9 (Gal-9) has tumor-selective and non-apoptotic cytotoxicity towards various types of cancer, which depended on autophagy inhibition. Thus, Gal-9 could be of therapeutic interest for (AraC-resistant) AML. In the current study, treatment with Gal-9 was cytotoxic for AML cells, including for CD34⁺ patient-derived AML stem cells, but not for healthy cord blood-derived CD34⁺ stem cells. This Gal-9-mediated cytotoxicity did not rely on apoptosis but was negatively associated with autophagic flux. Importantly, both AraC-sensitive and -resistant AML cell lines, as well as AML patient samples, were sensitive to single-agent treatment with Gal-9. Additionally, Gal-9 potentiated the cytotoxic effect of DNA demethylase inhibitor Azacytidine (Aza), a drug that is clinically used for patients that are not eligible for intensive AraC treatment. Thus, Gal-9 is a potential therapeutic agent for the treatment of AML, including AraC-resistant AML, by inducing caspase-independent cell death.

Selective inhibition of peptidyl-arginine deiminase (PAD): can it control multiple inflammatory disorders as a promising therapeutic strategy?

Peptidyl arginine deiminases (PADs) are a family of post-translational modification enzymes that irreversibly citrullinate (deiminate) arginine residues of protein and convert them to a non-classical amino acid citrulline in the presence of calcium ions. It has five isotypes, such as PAD1, PAD2, PAD3, PAD4, and PAD6, found in mammalian species. It has been suggested that increased PAD expression in various tissues contributes to the development of multiple inflammatory diseases, including rheumatoid arthritis (RA), cancer, diabetes, and neurological disorders. Elevation of PAD enzyme expression depends on several factors like rising intracellular Ca²⁺ levels, oxidative stress, and proinflammatory cytokines. PAD inhibitors originating from natural or synthetic sources can be used as a novel therapeutic approach concerning inflammatory disorders. Here, we review the pathological role of PAD in several inflammatory disorders, factors that trigger PAD expression, epigenetic role and finally, decipher the therapeutic approach of PAD inhibitors in multiple inflammatory disorders.

Increased Galectin-9 Levels Correlate with Disease Activity in Patients with DMARD-Naïve Rheumatoid Arthritis and Modulate the Secretion of MCP-1 and IL-6 from Synovial Fibroblasts

Background: Fibroblast-like synoviocytes (FLSs) are essential mediators in the expansive growth and invasiveness of rheumatoid synovitis, and patients with a fibroblastic-rich pauci-immune pathotype respond poorly to currently approved antirheumatic drugs. Galectin-9 (Gal-9) has been reported to directly modulate rheumatoid arthritis (RA) FLSs and to hold both pro- and anti-inflammatory properties. The objective of this study was to evaluate clinical and pathogenic aspects of Gal-9 in RA, combining national patient cohorts and cellular models. Methods: Soluble Gal-9 was measured in plasma from patients with newly diagnosed, treatment-naïve RA (n = 98). The disease activity score 28-joint count C-reactive protein (DAS28CRP) and total Sharp score were used to evaluate the disease course serially over a two-year period. Plasma and synovial fluid samples were examined for soluble Gal-9 in patients with established RA (n = 18). A protein array was established to identify Gal-9 binding partners in the extracellular matrix (ECM). Synovial fluid mononuclear cells (SFMCs), harvested from RA patients, were used to obtain synovial-fluid derived FLSs (SF-FLSs) (n = 7). FLSs from patients suffering from knee Osteoarthritis (OA) were collected from patients when undergoing joint replacement surgery (n = 5). Monocultures of SF-FLSs (n = 6) and autologous co-cultures of SF-FLSs and peripheral blood mononuclear cells (PBMCs) were cultured with and without a neutralizing anti-Gal-9 antibody (n = 7). The mono- and co-cultures were subsequently analyzed by flow cytometry, MTT assay, and ELISA. Results: Patients with early and established RA had persistently increased plasma levels of Gal-9 compared with healthy controls (HC). The plasma levels of Gal-9 were associated with disease activity and remained unaffected when adding a TNF-inhibitor to their standard treatment. Gal-9 levels were elevated in the synovial fluid of established RA patients with advanced disease, compared with corresponding plasma samples. Gal-9 adhered to fibronectin, laminin and thrombospondin, while not to interstitial collagens in the ECM protein array. In vitro, a neutralizing Gal-9 antibody decreased MCP-1 and IL-6 production from both RA FLSs and OA FLSs. In co-cultures of autologous RA FLSs and PBMCs, the neutralization of Gal-9 also decreased MCP-1 and IL-6 production, without affecting the proportion of inflammatory FLSs. Conclusions: In RA, pretreatment plasma Gal-9 levels in early RA were increased and correlated with clinical disease activity. Gal-9 levels remained increased despite a significant reduction in the disease activity score in patients with early RA. The in vitro neutralization of Gal-9 decreased both MCP-1 and IL-6 production in an inflammatory subset of RA FLSs. Collectively these findings indicate that the persistent overexpression of Gal-9 in RA may modulate synovial FLS activities and could be involved in the maintenance of subclinical disease activity in RA.

Peptidylarginine deiminase enzymes and citrullinated proteins in female reproductive physiology and associated diseases†

Citrullination, the post-translational modification of arginine residues, is catalyzed by the four catalytically active peptidylarginine deiminase (PAD or PADI) isozymes and alters charge to affect target protein structure and function. PADs were initially characterized in rodent uteri and, since then, have been described in other female tissues including ovaries, breast, and the lactotrope and gonadotrope cells of the anterior pituitary gland. In these tissues and cells, estrogen robustly stimulates PAD expression resulting in changes in levels over the course of the female reproductive cycle. The best-characterized targets for PADs are arginine residues in histone tails, which, when citrullinated, alter chromatin structure and gene expression. Methodological advances have allowed for the identification of tissue-specific citrullinomes, which reveal that PADs citrullinate a wide range of enzymes and structural proteins to alter cell function. In contrast to their important physiological roles, PADs and citrullinated proteins are also involved in several female-specific diseases including autoimmune disorders and reproductive cancers. Herein, we review current knowledge regarding PAD expression and function and highlight the role of protein citrullination in both normal female reproductive tissues and associated diseases.

Galectin-9: A novel promoter of atherosclerosis progression

BACKGROUND AND AIMS

Atherosclerosis is widely accepted to be an inflammatory disease driven by lipid accumulation and leukocyte recruitment. More recently, galectins, a family of β-galactoside binding proteins, have been shown to play a role in leukocyte recruitment among other immunomodulatory functions. Galectin (Gal) -9, a tandem repeat type galectin expressed by the endothelium in inflammatory environments, has been proposed to promote leukocyte recruitment. However, the role of Gal-9 in the context of monocyte recruitment remains elusive.

METHODS AND RESULTS

Here, we characterise the immunomodulatory role of Gal-9 in context of atherosclerosis. We show that ApoE-/-Gal-9-/- mice have a significantly reduced aortic plaque burden compared to their ApoE-/- littermate controls after 12 weeks of high fat diet. RNA sequencing data from two independent studies reveal Lgals9 expression in leukocyte clusters isolated from murine atherosclerotic plaques. Additionally, soluble Gal-9 protein induces monocyte activation and a pro-inflammatory phenotype in macrophages. Furthermore, we show that immobilised recombinant Gal-9 acts as capture and adhesion molecule for CD14+ monocytes in a β2-integrin and glycan dependent manner, while adhesion of monocytes to stimulated endothelium is reduced when Gal-9 is knocked down. Gal-9 also facilitates enhanced recruitment of leukocytes from peripheral arterial disease (PAD) patients compared to healthy young and aged controls. We further characterise the endothelium as source of circulating Gal-9, which is increased in plasma of PAD patients compared to healthy controls.

CONCLUSIONS

These results highlight a pathological role for Gal-9 as promoter of monocyte recruitment and atherosclerotic plaque progression, making it a novel target in the prevention of plaque formation and progression.

Galectin-9/Tim-3 pathway mediates dopaminergic neurodegeneration in MPTP-induced mouse model of Parkinson’s disease

Galectin-9 (Gal-9) is a crucial immunoregulatory mediator in the central nervous system. Microglial activation and neuroinflammation play a key role in the degeneration of dopaminergic neurons in the substantia nigra (SN) in Parkinson’s disease (PD). However, it remains unknown whether Gal-9 is involved in the pathogenesis of PD. We found that MPP+ treatment promoted the expression of Gal-9 and pro-inflammatory cytokines (IL-6, IL-1β, TNF-α, and MIP-1α) in a concentration-dependent manner in BV2 cells. Gal-9 enhanced neurodegeneration and oxidative stress induced by MPP+ in SH-SY5Y cells and primary neurons. Importantly, deletion of Gal-9 or blockade of Tim-3 ameliorated microglial activation, reduced dopaminergic neuronal loss, and improved motor performance in an MPTP-induced mouse model of PD. These observations demonstrate a pathogenic role of the Gal-9/Tim-3 pathway in exacerbating microglial activation, neuroinflammation, oxidative stress, and dopaminergic neurodegeneration in the pathogenesis of PD.

Galectin-9 supports primary T cell transendothelial migration in a glycan and integrin dependent manner

Adaptive immunity relies on the efficient recruitment of T cells from the blood into peripheral tissues. However, the current understanding of factor(s) coordinating these events is incomplete. Previous studies on galectin-9 (Gal-9), have proposed a functionally significant role for this lectin in mediating leukocyte adhesion and transmigration. However, very little is known about its function in T cell migration. Here, we have investigated the role of the Gal-9 on the migration behaviour of both human primary CD4⁺ and CD8⁺ T cells. Our data indicate that Gal-9 supports both CD4⁺ and CD8⁺ T cell adhesion and transmigration in a glycan dependent manner, inducing L-selectin shedding and upregulation of LFA-1 and CXCR4 expression. Additionally, when immobilized, Gal-9 promoted capture and firm adhesion of T cells under flow, in a glycan and integrin-dependent manner. Using an in vivo model, dorsal air pouch, we found that Gal-9 deficient mice display impaired leukocyte trafficking, with a reduction in pro-inflammatory cytokines/chemokines generated locally. Furthermore, we also demonstrate that Gal-9 inhibits the chemotactic function of CXCL12 through direct binding. In conclusion, our study characterises, for the first time, the capture, adhesion, and migration behaviour of CD4⁺ and CD8⁺ T cells to immobilised /endothelial presented Gal-9, under static and physiological flow conditions. We also demonstrate the differential binding characteristics of Gal-9 to T cell subtypes, which could be of potential therapeutic significance, particularly in the treatment of inflammatory-based diseases, given Gal-9 ability to promote apoptosis in pathogenic T cell subsets.

Galectin-9 Triggers Neutrophil-Mediated Anticancer Immunity

In earlier studies, galectin-9 (Gal-9) was identified as a multifaceted player in both adaptive and innate immunity. Further, Gal-9 had direct cytotoxic and tumor-selective activity towards cancer cell lines of various origins. In the current study, we identified that treatment with Gal-9 triggered pronounced membrane alterations in cancer cells. Specifically, phosphatidyl serine (PS) was rapidly externalized, and the anti-phagocytic regulator, CD47, was downregulated within minutes. In line with this, treatment of mixed neutrophil/tumor cell cultures with Gal-9 triggered trogocytosis and augmented antibody-dependent cellular phagocytosis of cancer cells. Interestingly, this pro-trogocytic effect was also due to the Gal-9-mediated activation of neutrophils with upregulation of adhesion markers and mobilization of gelatinase, secretory, and specific granules. These activation events were accompanied by a decrease in cancer cell adhesion in mixed cultures of leukocytes and cancer cells. Further, prominent cytotoxicity was detected when leukocytes were mixed with pre-adhered cancer cells, which was abrogated when neutrophils were depleted. Taken together, Gal-9 treatment potently activated neutrophil-mediated anticancer immunity, resulting in the elimination of epithelial cancer cells.

Galectin-9 mediates neutrophil capture and adhesion in a CD44 and β2 integrin-dependent manner

Neutrophil trafficking is a key component of the inflammatory response. Here, we have investigated the role of the immunomodulatory lectin Galectin-9 (Gal-9) on neutrophil recruitment. Our data indicate that Gal-9 is upregulated in the inflamed vasculature of RA synovial biopsies and report the release of Gal-9 into the extracellular environment following endothelial cell activation. siRNA knockdown of endothelial Gal-9 resulted in reduced neutrophil adhesion and neutrophil recruitment was significantly reduced in Gal-9 knockout mice in a model of zymosan-induced peritonitis. We also provide evidence for Gal-9 binding sites on human neutrophils; Gal-9 binding induced neutrophil activation (increased expression of β2 integrins and reduced expression of CD62L). Intra-vital microscopy confirmed a pro-recruitment role for Gal-9, with increased numbers of transmigrated neutrophils following Gal-9 administration. We studied the role of both soluble and immobilized Gal-9 on human neutrophil recruitment. Soluble Gal-9 significantly strengthened the interaction between neutrophils and the endothelium and inhibited neutrophil crawling on ICAM-1. When immobilized, Gal-9 functioned as an adhesion molecule and captured neutrophils from the flow. Neutrophils adherent to Gal-9 exhibited a spread/activated phenotype that was inhibited by CD18 and CD44 neutralizing antibodies, suggesting a role for these molecules in the pro-adhesive effects of Gal-9. Our data indicate that Gal-9 is expressed and released by the activated endothelium and functions both in soluble form and when immobilized as a neutrophil adhesion molecule. This study paves the way for further investigation of the role of Gal-9 in leukocyte recruitment in different inflammatory settings.

Association between inflammatory cytokines and immune-checkpoint molecule in rheumatoid arthritis

Background

Anti-citrullinated peptide antibodies (ACPA) and inflammatory cytokines play important roles in the development of rheumatoid arthritis (RA). T cell immunoglobulin and mucin–domain containing–3 (TIM–3) is an immune-checkpoint molecule involved in inhibitory signaling. Galectin–9 (Gal–9) mediated ligation of TIM–3 induces the amelioration of autoimmune diseases. TIM–3 is expressed in synovial osteoclasts and involved in the rheumatoid bone destruction. The aim of this study was to investigate the relationships between inflammatory cytokines and immune–checkpoint molecules in RA patients.

Methods

Serum levels of interleukin–6 (IL–6), tumor necrosis factor–α (TNF–α), soluble TIM–3 (sTIM–3) and Gal–9 were determined by ELISA. Patients were stratified into two groups based on ACPA titers: low-medium ACPA (ACPA <200 U/mL) and high ACPA (ACPA ≥200 U/mL). Serum levels of cytokines or immune-checkpoint molecules were evaluated between RA patients with low-medium ACPA titers and high ACPA titers.

Results

Elevated serum levels of inflammatory cytokines were correlated with DAS28–ESR in RA patients. Although serum levels of sTIM–3 were elevated in RA patients, significant correlations between sTIM–3 and cytokines (IL–6 or TNF–α) were observed exclusively in RA patients with low-medium ACPA titers (<200 U/mL). Serum levels of IL–6 and TNF–α levels were significantly correlated with elevated Gal–9 levels regardless of ACPA status. A significant correlation between IL–6 and Gal–9 was observed in RA patients without advanced joint damage. Conversely, a significant correlation between TNF–α and Gal–9 was observed in RA patients with advanced joint damage.

Conclusions

Our data indicated that there are positive correlations between circulating inflammatory cytokines and checkpoint molecules in RA patients and these interactions can be modulated by ACPA status or joint damage stage.

Neutrophils promote T-cell activation through the regulated release of CD44-bound Galectin-9 from the cell surface during HIV infection

The interaction of neutrophils with T cells has been the subject of debate and controversies. Previous studies have suggested that neutrophils may suppress or activate T cells. Despite these studies, the interaction between neutrophils and T cells has remained a largely unexplored field. Here, based on our RNA sequencing (RNA-seq) analysis, we found that neutrophils have differential transcriptional and functional profiling depending on the CD4 T-cell count of the HIV-infected individual. In particular, we identified that neutrophils in healthy individuals express surface Galectin-9 (Gal-9), which is down-regulated upon activation, and is consistently down-regulated in HIV-infected individuals. However, down-regulation of Gal-9 was associated with CD4 T-cell count of patients. Unstimulated neutrophils express high levels of surface Gal-9 that is bound to CD44, and, upon stimulation, neutrophils depalmitoylate CD44 and induce its movement out of the lipid raft. This process causes the release of Gal-9 from the surface of neutrophils. In addition, we found that neutrophil-derived exogenous Gal-9 binds to cell surface CD44 on T cells, which promotes LCK activation and subsequently enhances T-cell activation. Furthermore, this process was regulated by glycolysis and can be inhibited by interleukin (IL)-10. Together, our data reveal a novel mechanism of Gal-9 shedding from the surface of neutrophils. This could explain elevated plasma Gal-9 levels in HIV-infected individuals as an underlying mechanism of the well-characterized chronic immune activation in HIV infection. This study provides a novel role for the Gal-9 shedding from neutrophils. We anticipate that our results will spark renewed investigation into the role of neutrophils in T-cell activation in other acute and chronic conditions, as well as improved strategies for modulating Gal-9 shedding.

This study shows that HIV-infected individuals have different neutrophil profiles depending on their CD4 T cell count. In particular, neutrophils express high levels of surface Gal-9 but this is shed upon stimulation; this exogenous Gal-9 binds to CD44 on T cells, which promotes LCK activation and subsequently enhances T cell activation.

Gene polymorphisms of LGALS2, LGALS3 and LGALS9 in patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is a complicated rheumatic autoimmune disease. Lectin, galactoside-binding soluble, 2 (LGALS2), LGALS3 and LGALS9, three members of the galectin family, play potential roles in autoimmune diseases, including RA. However, association of genetic polymorphisms of LGALS2, LGALS3 and LGALS9 with RA risk in a Southern Chinese Han population has not been elucidated. A case-control study was conducted herein, including 500 RA patients and 650 healthy individuals of Southern Chinese Han origin. Twelve single nucleotide polymorphisms (SNPs), including rs7291467 for the LGALS2 gene, rs4644, rs4652, rs1009977, rs2274273 and rs17128183 for the LGALS3 gene, and rs4795835, rs3763959, rs4239242, rs3751093, rs732222 and rs4794976 for the LGALS9 gene, were genotyped. Polymorphisms were genotyped using the KASP method. Frequencies of rs1009977 genotype TG and rs3751093 genotype GA of LGALS3 gene were significantly different between RA patients and healthy controls (P = 0.049, P = 0.033). Allele T and genotypes TT and TT + TG of rs4794976 for LGALS9 gene were significantly correlated with RA risk (P = 0.017, P = 0.012, P = 0.041). Subgroup analysis revealed that rs1009977, rs2274273 and rs17128183 polymorphisms of LGALS3 gene and rs4795835 polymorphism of LGALS9 gene were correlated with several RA clinical manifestations (all P < 0.05). In addition, haplotype GCGTT showed an increased risk for RA (OR = 1.216, 95% CI: 1.028-1.438, P = 0.023), whereas haplotype GCGTG showed a reduced risk for RA susceptibility (OR = 0.779, 95% CI: 0.625-0.971, P = 0.026). In conclusion, LGALS3 and LGALS9 gene polymorphisms may associate with RA predisposition in a Southern Chinese Han population.

Emerging role of galectin family in inflammatory autoimmune diseases

Galectin family is a group of glycan-binding proteins. Members in this family are expressed in different tissues, immune or non-immune cells. These molecules are important regulators in innate and adaptive immune response, performing significantly in a broad range of cellular and pathophysiological functions, such as cell proliferation, adhesion, migration, and invasion. Findings have shown that expression of galectins is abnormal in many inflammatory autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, osteoarthritis, sjögren's syndrome, systemic sclerosis. Galectins also function as intracellular and extracellular disease regulators mainly through the binding of their carbohydrate recognition domain to glycoconjugates. Here, we review the state-of-the-art of the role that different galectin family members play in immune cells, contributing to the complex inflammatory diseases. Hopefully collection of the information will provide a preliminary theoretical basis for the exploration of new targets for treatment of the disorders.

Aberrantly Expressed Galectin-9 Is Involved in the Immunopathogenesis of Anti-MDA5-Positive Dermatomyositis-Associated Interstitial Lung Disease

Background

Dermatomyositis (DM) associated rapidly progressive interstitial lung disease (RP-ILD) has high mortality rate and poor prognosis. Galectin-9 (Gal-9) plays multiple functions in immune regulation. We investigated Gal-9 expression in DM patients and its association with DM-ILD.

Methods

A total of 154 idiopathic inflammatory myopathy patients and 30 healthy controls were enrolled in the study. Cross-sectional and longitudinal studies were used to analyze the association between serum Gal-9 levels and clinical features. Enzyme-linked immunosorbent assay and qRT-PCR were used to examine Gal-9 expression in the sera and isolated peripheral blood mononuclear cells (PBMCs) from DM patients. Immunohistochemistry was performed to analyze the expression of Gal-9 and its ligand (T-cell immunoglobulin mucin (Tim)-3 and CD44) in lung tissues from anti-melanoma differentiation-associated gene 5 (MDA5)-positive patients. The effect of Gal-9 on human lung fibroblasts (MRC-5) was investigated in vitro.

Results

Serum Gal-9 levels were significantly higher in DM patients than in immune-mediated necrotizing myopathy patients and healthy controls (all p < 0.001). Higher serum Gal-9 levels were observed in anti-MDA5-positive DM patients than in anti-MDA5-negative DM patients [33.8 (21.9–44.7) vs. 16.2 (10.0–26.9) ng/mL, p < 0.001]. Among the anti-MDA5-positive DM patients, serum Gal-9 levels were associated with RP-ILD severity. Serum Gal-9 levels were significantly correlated with disease activity in anti-MDA5-positive DM patients in both cross-sectional and longitudinal studies. PBMCs isolated from anti-MDA5-positive DM patients (3.7 ± 2.3 ng/mL) produced higher levels of Gal-9 than those from immune-mediated necrotizing myopathy patients (1.1 ± 0.3 ng/mL, p = 0.022) and healthy controls (1.4 ± 1.2 ng/mL, p = 0.045). The mRNA levels of Gal-9 were positively correlated with the levels of type-I interferon-inducible genes MX1 (r = 0.659, p = 0.020) and IFIH1 (r = 0.787, p = 0.002) in PBMCs from anti-MDA5-positive DM patients. Immunohistochemistry revealed increased Gal-9 and Tim-3 expression in the lung tissues of patients with DM and RP-ILD. In vitro stimulation with Gal-9 protein increased CCL2 mRNA expression in MRC-5 fibroblasts.

Conclusions

Among anti-MDA5-positive DM patients, Gal-9 could be a promising biomarker for monitoring disease activity, particularly for RP-ILD severity. Aberrant expression of the Gal-9/Tim-3 axis may be involved in the immunopathogenesis of DM-ILD.

Excessive Neutrophils and Neutrophil Extracellular Traps in COVID-19

Background: Cases of excessive neutrophil counts in the blood in severe coronavirus disease (COVID-19) patients have drawn significant attention. Neutrophil infiltration was also noted on the pathological findings from autopsies. It is urgent to clarify the pathogenesis of neutrophils leading to severe pneumonia in COVID-19. Methods: A retrospective analysis was performed on 55 COVID-19 patients classified as mild (n = 22), moderate (n = 25), and severe (n = 8) according to the Guidelines released by the National Health Commission of China. Trends relating leukocyte counts and lungs examined by chest CT scan were quantified by Bayesian inference. Transcriptional signatures of host immune cells of four COVID19 patients were analyzed by RNA sequencing of lung specimens and BALF. Results: Neutrophilia occurred in 6 of 8 severe patients at 7-19 days after symptom onset, coinciding with lesion progression. Increasing neutrophil counts paralleled lesion CT values (slope: 0.8 and 0.3-1.2), reflecting neutrophilia-induced lung injury in severe patients. Transcriptome analysis revealed that neutrophil activation was correlated with 17 neutrophil extracellular trap (NET)-associated genes in COVID-19 patients, which was related to innate immunity and interacted with T/NK/B cells, as supported by a protein-protein interaction network analysis. Conclusion: Excessive neutrophils and associated NETs could explain the pathogenesis of lung injury in COVID-19 pneumonia.

Pulmonary Neutrophilic Inflammation and Noncommunicable Diseases: Pathophysiology, Redox Mechanisms, Biomarkers, and Therapeutics

Significance: Pulmonary neurophilic inflammation (PNI) is the homing and activation of neutrophil with damage to the microvasculature. This process is involved in pulmonary damage in patients exposed to airborne pollutants (exogenous stressors) and also to systemic inflammation/oxidative stress (endogenous stressors) associated with noncommunicable diseases (NCDs). Recent Advances: PNI is an important trigger of the early onset and progression of NCD in susceptible patients exposed to airborne pollutants. Irritation of the lung microvasculature by exogenous and endogenous stressors causes PNI. Circulating endogenous stressors in NCD can cause PNI. Critical Issues: Air pollution-triggered PNI causes increased circulating endogenous stressors that can trigger NCD in susceptible patients. Systemic inflammation/oxidative stress associated with NCD can cause PNI. Inflammation/end-oxidation products of macromolecules are also potential biomarkers and therapeutic targets for NCD-triggered PNI- and PNI-triggered NCD. Future Directions: Understanding the molecular mechanism of PNI triggered by exogenous or endogenous stressors will help explain the early onset of NCD in susceptible patients exposed to air pollution. It can also help undercover biomarkers and mechanism-based therapeutic targets in air pollutant-triggered PNI, PNI-triggered NCD, and NCD-triggered PNI.

Differential regulation and correlation between galectin-9 and anti-CCP antibody (ACPA) in rheumatoid arthritis patients

Background

Galectin-9 (Gal-9) is involved in the regulatory process of immune responses or inflammation. The aim of the present study is to characterize circulating Gal-9 in patients with rheumatoid arthritis (RA) and its relationship with RA disease activity and phenotype.

Methods

A total of 116 RA patients and 31 age-matched healthy controls were included in this study. Disease activity of RA patients was determined by Disease Activity Score of 28 joint scoring system (DAS28-ESR). Levels of Gal-9 in serum were determined by enzyme-linked immunosorbent assay (ELISA).

Results

Serum levels of Gal-9 were significantly higher in patients with RA compared to those in controls (median 7577 pg/ml [interquartile range (IQR) 5570–10,201] versus 4738 pg/ml [IQR 4267–5630], p = 0.001). There were significant differences in serum Gal-9 between RA patients with and without RA-ILD (9606 pg/ml [IQR 8522–12,167] versus 7078 pg/ml [IQR 5225–9447], p < 0.001) or those with and without advanced joint damage (stage II–IV, 9606 pg/ml [IQR 8522–12,167] versus 7078 pg/ml [IQR 5225–9447], p < 0.001). Although serum levels of Gal-9 correlated with the titers of ACPA (r = 0.275, p = 0.002), levels of ACPA titers conferred the different relationship, between serum Gal-9 and inflammatory mediators or RA disease activity. Although Gal-9 was correlated with ACPA titers (r = 0.508, p = 0.002), there was no correlation between Gal-9 levels and erythrocyte sedimentation rate (ESR), matrix metalloproteinase-3 (MMP-3), or DAS28-ESR in RA patients with high titers of ACPA (> 200 U/ml). Conversely, Gal-9 was correlated with MMP-3 (r = 0.300, p = 0.007) or DAS28-ESR (r = 0.331, p = 0.004) but not with ACPA titer in RA patients with low titers of ACPA titers (< 200 U/ml).

Conclusions

Serum levels of Gal-9 were increased in RA patients and associated with RA disease activity in RA patients without high titers of ACPA. The levels of ACPA titers may influence the values of circulating Gal-9 in RA patients with various clinical phenotypes. These data suggest that Gal-9 possessed the properties of pro-inflammatory or arthropathic biomarker under the status of ACPA titers.