Galectin-9 Is Critical for Mucosal Adaptive Immunity through the T Helper 17-IgA Axis

All roads lead to IgA: Mapping the many pathways of IgA induction in the gut

The increasing prevalence of food allergy and related pathologies in recent years has underscored the need to understand the factors affecting adverse reactions to food. Food allergy is caused when food-specific IgE triggers the release of histamine from mast cells. However, other food-specific antibody isotypes exist as well, including IgG and IgA. IgA is the main antibody isotype in the gut and mediates noninflammatory reactions to toxins, commensal bacteria, and food antigens. It has also been thought to induce tolerance to food, thus antagonizing the role of food-specific IgE. However, this has remained unclear as food-specific IgA generation is poorly understood. Particularly, the location of IgA induction, the role of T cell help, and the fates of food-specific B cells remain elusive. In this review, we outline what is known about food-specific IgA induction and highlight areas requiring further study. We also explore how knowledge of food-specific IgA induction can be informed by and subsequently contribute to our overall knowledge of gut immunity.

ATXN3 functions as a tumor suppressor through potentiating galectin-9-mediated apoptosis in human colon adenocarcinoma

While deubiquitinase ATXN3 has been implicated as a potential oncogene in various types of human cancers, its role in colon adenocarcinoma remains understudied. Surprisingly, our findings demonstrate that ATXN3 exerts an antitumor effect in human colon cancers through potentiating Galectin-9-induced apoptosis. CRISPR-mediated ATXN3 deletion unexpectedly intensified colon cancer growth both in vitro and in xenograft colon cancers. At the molecular level, we identified ATXN3 as a bona fide deubiquitinase specifically targeting Galectin-9, as ATXN3 interacted with and inhibited Galectin-9 ubiquitination. Consequently, targeted ATXN3 ablation resulted in reduced Galectin-9 protein expression, thereby diminishing Galectin-9-induced colon cancer apoptosis and cell growth arrest. The ectopic expression of Galectin-9 fully reversed the growth of ATXN3-null colon cancer in mice. Furthermore, immunohistochemistry staining revealed a significant reduction in both ATXN3 and Galectin-9 protein expression, along with a positive correlation between them in human colon cancer. Our study identifies the first Galectin-9-specific deubiquitinase and unveils a tumor-suppressive role of ATXN3 in human colon cancer.

Potential of algae-derived alginate oligosaccharides and β-glucan to counter inflammation in adult zebrafish intestine

Alginate oligosaccharides (AOS) are natural bioactive compounds with anti-inflammatory properties. We performed a feeding trial employing a zebrafish (Danio rerio) model of soybean-induced intestinal inflammation. Five groups of fish were fed different diets: a control (CT) diet, a soybean meal (SBM) diet, a soybean meal+β-glucan (BG) diet and 2 soybean meal+AOS diets (alginate products differing in the content of low molecular weight fractions - AL, with 31% < 3kDa and AH, with 3% < 3kDa). We analyzed the intestinal transcriptomic and plasma metabolomic profiles of the study groups. In addition, we assessed the expression of inflammatory marker genes and histological alterations in the intestine. Dietary algal β-(1, 3)-glucan and AOS were able to bring the expression of certain inflammatory genes altered by dietary SBM to a level similar to that in the control group. Intestinal transcriptomic analysis indicated that dietary SBM changed the expression of genes linked to inflammation, endoplasmic reticulum, reproduction and cell motility. The AL diet suppressed the expression of genes related to complement activation, inflammatory and humoral response, which can likely have an inflammation alleviation effect. On the other hand, the AH diet reduced the expression of genes, causing an enrichment of negative regulation of immune system process. The BG diet suppressed several immune genes linked to the endopeptidase activity and proteolysis. The plasma metabolomic profile further revealed that dietary SBM can alter inflammation-linked metabolites such as itaconic acid, taurochenodeoxycholic acid and enriched the arginine biosynthesis pathway. The diet AL helped in elevating one of the short chain fatty acids, namely 2-hydroxybutyric acid while the BG diet increased the abundance of a vitamin, pantothenic acid. Histological evaluation revealed the advantage of the AL diet: it increased the goblet cell number and length of villi of the intestinal mucosa. Overall, our results indicate that dietary AOS with an appropriate amount of < 3kDa can stall the inflammatory responses in zebrafish.

The role of galectins in immunity and infection

The galectin family consists of carbohydrate (glycan) binding proteins that are expressed by a wide variety of cells and bind to galactose-containing glycans. Galectins can be located in the nucleus or the cytoplasm, or can be secreted into the extracellular space. They can modulate innate and adaptive immune cells by binding to glycans on the surface of immune cells or intracellularly via carbohydrate-dependent or carbohydrate-independent interactions. Galectins expressed by immune cells can also participate in host responses to infection by directly binding to microorganisms or by modulating antimicrobial functions such as autophagy. Here we explore the diverse ways in which galectins have been shown to impact immunity and discuss the opportunities and challenges in the field.

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 Is a Novel Regulator of Epithelial Restitution

Increasingly, the ß-galactoside binding lectins, termed galectins, are being recognized as critical regulators of cell function and organismal homeostasis. Within the context of the mucosal surface, galectins are established regulators of innate and adaptive immune responses, microbial populations, and several critical epithelial functions, including cell migration, proliferation, and response to injury. However, given their complex tissue distribution and expression patterns, their role within specific processes remains poorly understood. We took a genetic approach to understand the role of endogenous galectin-9 (Gal-9), a mucosal galectin that has been linked to inflammatory bowel disease, within the context of the murine intestine. Gal-9-deficient (Gal9^-/-, also known as Lgals9^-/-) animals show increased sensitivity to chemically induced colitis and impaired proliferation in the setting of acute injury. Moreover, Gal9^-/--derived enteroids showed impaired growth ex vivo. Consistent with a model in which endogenous Gal-9 controls epithelial growth and repair, Gal9^-/- animals showed increased sensitivity to intestinal challenge in multiple models of epithelial injury, including acute irradiation injury and ectopic wound biopsies. Finally, regenerating crypts from patient biopsies showed increased expression of Gal-9, indicating these processes may be conserved in humans. Taken together, these studies implicate Gal-9 in the regulation of cellular proliferation and epithelial restitution after intestinal epithelial injury.

Intracellular Galectin-9 Enhances Proximal TCR Signaling and Potentiates Autoimmune Diseases

Galectin-9 is a risk gene in inflammatory bowel disease. By transcriptomic analyses of ileal biopsies and PBMCs from inflammatory bowel disease patients, we identified a positive correlation between galectin-9 expression and colitis severity. We observed that galectin-9-deficient T cells were less able to induce T cell-mediated colitis. However, several mouse-based studies reported that galectin-9 treatment induces T cell apoptosis and ameliorates autoimmune diseases in an exogenously modulated manner, indicating a complicated regulation of galectin-9 in T cells. We found that galectin-9 is expressed mainly inside T cells, and its secreted form is barely detected under physiological conditions. Endogenous galectin-9 was recruited to immune synapses upon T cell activation. Moreover, proximal TCR signaling was impaired in galectin-9-deficient T cells, and proliferation of these cells was decreased through an intracellularly modulated manner. Th17 cell differentiation was downregulated in galectin-9-deficient T cells, and this impairment can be rescued by strong TCR signaling. Taken together, these findings suggest that intracellular galectin-9 is a positive regulator of T cell activation and modulates the pathogenesis of autoimmune diseases.

Role of Galectin-9 in Atopic Dermatitis - Is It Mediated Through E Selectin? A Clinical and Immunohistochemical Study

Background

Atopic dermatitis (AD) is a recognized T helper (Th)2, allergic, skin disease. Galectin-9 (gal-9) is a member of galectin family. It alters T-cell balance resulting in Th2 polarization. These Th2 cells yield various cytokines that may influence E selectin expression. Therefore, we hypothesized that gal-9 may have an active role in AD and this role could be mediated through E selectin.

Objective

To assess this hypothesis, immunohistochemical expression of gal-9 and E selectin was investigated in skin lesions, from atopic dermatitis patients, and compared.

Methods

Twenty-two atopic dermatitis patients and ten controls were included in this case-control study. SCORAD score was used to evaluate atopic dermatitis severity. Biopsies from skin lesions of AD patients and matched sites of controls were taken and stained immunohistochemically by gal-9 and E selectin polyclonal antibodies.

Results

Compared to controls, atopic dermatitis patients exhibited a significant increased gal-9 H score, percent of expression, cellular localization (P˂0.001) and intensity (P=0.04) as well as dermal cellular infiltrate (P˂0.001). Also, there were significant elevations in E selectin H score (P=0.002), percent of expression (P=0.001) and cellular localization (P<0.001) as well as dermal inflammatory infiltrates in AD cases than controls. In AD, 20 cases showed co expression of both gal-9 and E selectin in the epidermis with insignificant correlation between their H scores.

Study Limitations

This study only included a small number of studied subjects.

Conclusion

Galectin-9 and E selectin participates independently in atopic dermatitis pathogenesis, that may help in development of new therapeutic agents in atopic dermatitis management program.

Aspergillus fumigatus enhances human NK cell activity by regulating M1 macrophage polarization

The progression of disease caused by fungal infection is closely associated with the human immune system. Macrophages and natural killer cells (NK cells) are two important types of innate immune cells that serve an important role in anti-infection immunity. There has been limited research into the interactions between fungi and macrophages. In the present in vitro study, reverse transcription-quantitative PCR, ELISA and flow cytometry were performed to reveal that the interaction between macrophages and NK cells, regulated by Aspergillus fumigatus conidia, induced macrophages to polarize into M1 macrophages by secreting large quantities of tumor necrosis factor-α, interleukin-18 and Galectin-9. In addition, when NK cells were co-cultured with the conidia of A. fumigatus-stimulated M1 macrophages, they exhibited increased activation levels and secretion of interferon-γ (IFN-γ). It was further demonstrated via antibody neutralization and gene silencing experiments that galectin-9 served an important role in the interaction between macrophages and NK cells regulated by A. fumigatus. In conclusion, it was demonstrated that A. fumigatus induced the polarization of macrophages into M1 macrophages by secreting Galectin-9, which then promoted NK cell activity and IFN-γ secretion. The results provided improved understanding of the role of innate immune cells in invasive fungal infections. The present study also provided novel insight into the study of macrophages and NK cells in inflammatory infections caused by A. fumigatus and potential strategies to control the progression of inflammation.