Galectin-1 Suppresses Autoimmune Retinal Disease by Promoting Concomitant Th2- and T Regulatory-Mediated Anti-Inflammatory Responses

Fine-tuning antitumor responses through the control of galectin-glycan interactions: an overview

In recent years, we have witnessed critical advances in genomics and proteomics which contributed to delineate the "tumor progression signature". This includes the altered expression of genes and proteins not only in tumor cells, but also in tumor-associated stromal, endothelial, and immune cells. Adding more complexity to this bewildering information, efforts are being made to define the "glycosylation signature" of the tumor microenvironment, which results from the abnormal expression and activity of glycosyltransferases, glycosidases, and enzyme chaperons. The multiple combinatorial possibilities of glycan structures expressed by neoplastic versus normal tissue provide enormous potential for information display and expand potential therapeutic opportunities. The responsibility of deciphering the biological information encoded by the tumor-associated glycome is partially assigned, to distinct families of endogenous glycan-binding proteins or lectins, whose expression and function are regulated in cancerous tissues. Galectins, a family of evolutionarily conserved glycan-binding proteins, can control tumor progression by directly influencing tumor growth or by modulating cell migration, angiogenesis, and tumor-immune escape. In this review, we will highlight recent findings on how galectin-glycan lattices control the dialogue between tumor and immune cells and how these interactions could be exploited for therapeutic purposes.

Characterization and functionality of proliferative human Sertoli cells

It has long been thought that mammalian Sertoli cells are terminally differentiated and nondividing postpuberty. For most previous in vitro studies immature rodent testes have been the source of Sertoli cells and these have shown little proliferative ability when cultured. We have isolated and characterized Sertoli cells from human cadaveric testes from seven donors ranging from 12 to 36 years of age. The cells proliferated readily in vitro under the optimized conditions used with a doubling time of approximately 4 days. Nuclear 5-ethynyl-2'-deoxyuridine (EdU) incorporation confirmed that dividing cells represented the majority of the population. Classical Sertoli cell ultrastructural features, lipid droplet accumulation, and immunoexpression of GATA-4, Sox9, and the FSH receptor (FSHr) were observed by electron and fluorescence microscopy, respectively. Flow cytometry revealed the expression of GATA-4 and Sox9 by more than 99% of the cells, and abundant expression of a number of markers indicative of multipotent mesenchymal cells. Low detection of endogenous alkaline phosphatase activity after passaging showed that few peritubular myoid cells were present. GATA-4 and SOX9 expression were confirmed by reverse transcription polymerase chain reaction (RT-PCR), along with expression of stem cell factor (SCF), glial cell line-derived neurotrophic factor (GDNF), and bone morphogenic protein 4 (BMP4). Tight junctions were formed by Sertoli cells plated on transwell inserts coated with fibronectin as revealed by increased transepithelial electrical resistance (TER) and polarized secretion of the immunoregulatory protein, galectin-1. These primary Sertoli cell populations could be expanded dramatically in vitro and could be cryopreserved. The results show that functional human Sertoli cells can be propagated in vitro from testicular cells isolated from adult testis. The proliferative human Sertoli cells should have important applications in studying infertility, reproductive toxicology, testicular cancer, and spermatogenesis, and due to their unique biological properties potentially could be useful in cell therapy.

Development of a nascent galectin-1 chimeric molecule for studying the role of leukocyte galectin-1 ligands and immune disease modulation

Galectin-1 (Gal-1), a β-galactoside-binding lectin, plays a profound role in modulating adaptive immune responses by altering the phenotype and fate of T cells. Experimental data showing recombinant Gal-1 (rGal-1) efficacy on T cell viability and cytokine production, nevertheless, is controversial due to the necessity of using stabilizing chemicals to help retain Gal-1 structure and function. To address this drawback, we developed a mouse Gal-1 human Ig chimera (Gal-1hFc) that did not need chemical stabilization for Gal-1 ligand recognition, apoptosis induction, and cytokine modulation in a variety of leukocyte models. At high concentrations, Gal-1hFc induced apoptosis in Gal-1 ligand(+) Th1 and Th17 cells, leukemic cells, and granulocytes from synovial fluids of patients with rheumatoid arthritis. Importantly, at low, more physiologic concentrations, Gal-1hFc retained its homodimeric form without losing functionality. Not only did Gal-1hFc-binding trigger IL-10 and Th2 cytokine expression in activated T cells, but members of the CD28 family and several other immunomodulatory molecules were upregulated. In a mouse model of contact hypersensitivity, we found that a non-Fc receptor-binding isoform of Gal-1hFc, Gal-1hFc2, alleviated T cell-dependent inflammation by increasing IL-4(+), IL-10(+), TGF-β(+), and CD25(high)/FoxP3(+) T cells, and by decreasing IFN-γ(+) and IL-17(+) T cells. Moreover, in human skin-resident T cell cultures, Gal-1hFc diminished IL-17(+) T cells and increased IL-4(+) and IL-10(+) T cells. Gal-1hFc will not only be a useful new tool for investigating the role of Gal-1 ligands in leukocyte death and cytokine stimulation, but for studying how Gal-1-Gal-1 ligand binding shapes the intensity of immune responses.

Galectin inhibitory disaccharides promote tumour immunity in a breast cancer model

High level galectin-1 expression results in cancer cell evasion of the immune response, increased tumour survival and aggressive metastases. Using a galectin-1 polyclonal antibody, high levels of galectin-1 protein were shown to be expressed by breast cancer cells established from FVB/N MMTV-c-neu mice as well as by the B16F10 melanoma cell line. In mixed lymphocyte cultures using tumour cells as antigenic stimulators, addition of recombinant galectin-1 dose-dependently inhibited lymphocyte production. Disaccharides were identified that inhibited galectin-1 function and increased growth and activation of CD8(+) CTL's killing cancer cells. X-ray crystallographic structures of human galectin-1 in complex with inhibitory disaccharides revealed their mode of binding. Combining galectin-blocking carbohydrates as adjuvants with vaccine immunotherapy in vivo to promote immune responses significantly decreased tumour progression and improved the outcomes for tumour challenged mice. This is the first report showing that suitably selected galectin-1 blocking disaccharides will act as adjuvants promoting vaccine stimulated immune responses against tumours in vivo.

Lack of TNFR p55 results in heightened expression of IFN-γ and IL-17 during the development of reactive arthritis

Reactive arthritis (ReA) is a type of arthritis originating from certain gastrointestinal or genitourinary infections. In previous studies, we reported the development of progressive Yersinia enterocolitica-induced ReA in mice lacking TNFR p55; however, the mechanisms underlying this effect are still uncertain. In this study, we investigated the impact of TNFR p55 deficiency in modulating Ag-specific Th1 and Th17 responses during this arthritogenic process. We found more severe ReA in TNFRp55(-/-) mice compared with their wild-type (WT) counterparts. This effect was accompanied by increased levels of Yersinia LPS in the joints of knockout mice. Analysis of the local cytokine profile revealed greater amounts of IFN-γ and IL-17 in arthritic joints of TNFRp55(-/-) mice compared with WT mice at day 21 postinfection. Moreover, altered IL-17 and IFN-γ production was observed in mesenteric and inguinal lymph nodes of Yersinia-infected TNFRp55(-/-) mice, as well as in spleen cells obtained from infected mice and restimulated ex vivo with bacterial Ags. Increased levels of cytokine secretion were associated with a greater frequency of CD4(+)IL-17(+), CD4(+)IFN-γ(+), and IL-17(+)IFN-γ(+) cells in TNFRp55(-/-) mice compared with WT mice. Remarkably, Ab-mediated blockade of IL-17 and/or IFN-γ resulted in reduced joint histological scores in TNFRp55(-/-) mice. A mechanistic analysis revealed the involvement of p40, a common subunit of heterodimeric IL-12 and IL-23, in the generation of augmented IFN-γ and IL-17 production under TNFR p55 deficiency. Taken together, these data indicate that, in the absence of TNFR p55 signaling, Th1 and Th17 effector cells may act in concert to sustain the inflammatory response in bacterial-induced arthritogenic processes.

R, Sant’Anna OA, Rizzo LV. Autoimmune uveitis: study of treatment therapies

ABSTRACT Experimental autoimmune uveitis is an organ-specific T-cell mediated autoimmune disease characterized by inflammation and consequent destruction of the neural retina and adjacent tissues. Inflammation in experimental autoimmune uveitis may be induced in rodents by immunization with retinal antigens, such as interphotoreceptor retinoid-binding protein. We present a review of experimental studies that correlate primary immunobiological functions with this chronic disease and the possible use of molecules for the treatment of autoimmune uveitis.

Multiple functional targets of the immunoregulatory activity of galectin-1: Control of immune cell trafficking, dendritic cell physiology, and T-cell fate

In the postgenomic era, the study of the glycome-the whole repertoire of saccharides in cells and tissues-has enabled the association of unique glycan structures with specific physiological and pathological processes. The responsibility for deciphering this biological information belongs to endogenous glycan-binding proteins or lectins. Galectin-1, a prototypic member of a family of structurally related proteins, has demonstrated selective antiinflammatory and immunoregulatory effects either by controlling immune cell trafficking, "fine-tuning" dendritic cell physiology and regulating T-cell fate. These regulatory functions mediated by an endogenous glycan-binding protein may contribute to fulfill the needs for immune cell homeostasis, including preservation of fetomaternal tolerance and prevention of collateral damage as a result of microbial invasion or autoimmune pathology. We will discuss here the conceptual framework which led to the study of galectin-glycan lattices as a novel paradigm of immune cell communication in physiological and pathological processes and will highlight selected methods and experimental strategies which have contributed to the study of the immunoregulatory activities of this multifaceted glycan-binding protein both in in vitro and in vivo biological settings.

Conveying glycan information into T-cell homeostatic programs: a challenging role for galectin-1 in inflammatory and tumor microenvironments

The immune system has evolved sophisticated mechanisms composed of several checkpoints and fail-safe processes that enable it to orchestrate innate and adaptive immunity, while at the same time limiting aberrant or unfaithful T-cell function. These multiple regulatory pathways take place during the entire life-span of T cells including T-cell development, homing, activation, and differentiation. Galectin-1, an endogenous glycan-binding protein widely expressed at sites of inflammation and tumor growth, controls a diversity of immune cell processes, acting either extracellularly through specific binding to cell surface glycan structures or intracellularly through modulation of pathways that remain largely unexplored. In this review, we highlight the discoveries that have led to our current understanding of the role of galectin-1 in distinct immune cell process, particularly those associated with T-cell homeostasis. Also, we emphasize findings emerging from the study of experimental models of autoimmunity, chronic inflammation, fetomaternal tolerance, and tumor growth, which have provided fundamental insights into the critical role of galectin-1 and its specific saccharide ligands in immunoregulation. Challenges for the future will embrace the rational manipulation of galectin-1-glycan interactions both towards attenuating immune responses in autoimmune diseases, graft rejection, and recurrent fetal loss, while at the same overcoming immune tolerance in chronic infections and cancer.

Galectin 3 induces a distinctive pattern of cytokine and chemokine production in rheumatoid synovial fibroblasts via selective signaling pathways

OBJECTIVE

High expression of galectin 3 at sites of joint destruction in rheumatoid arthritis (RA) suggests that galectin 3 plays a role in RA pathogenesis. Previous studies have demonstrated the effects of galectins on immune cells, such as lymphocytes and macrophages. This study was undertaken to investigate the hypothesis that galectin 3 induces proinflammatory effects in RA by modulating the pattern of cytokine and chemokine production in synovial fibroblasts.

METHODS

Matched samples of RA synovial and skin fibroblasts were pretreated with galectin 3 or tumor necrosis factor alpha (TNFalpha), and the levels of a panel of cytokines, chemokines, and matrix metalloproteinases (MMPs) were determined using enzyme-linked immunosorbent assays and multiplex assays. Specific inhibitors were used to dissect signaling pathways, which were confirmed by Western blotting and NF-kappaB activation assay.

RESULTS

Galectin 3 induced secretion of interleukin-6 (IL-6), granulocyte-macrophage colony-stimulating factor, CXCL8, and MMP-3 in both synovial and skin fibroblasts. By contrast, galectin 3-induced secretion of TNFalpha, CCL2, CCL3, and CCL5 was significantly greater in synovial fibroblasts than in skin fibroblasts. TNFalpha blockade ruled out autocrine TNFalpha-stimulated induction of chemokines. The MAPKs p38, JNK, and ERK were necessary for IL-6 production, but phosphatidylinositol 3-kinase (PI 3-kinase) was required for selective CCL5 induction. NF-kappaB activation was required for production of both IL-6 and CCL5.

CONCLUSION

Our findings indicate that galectin 3 promotes proinflammatory cytokine secretion by tissue fibroblasts. However, galectin 3 induces the production of mononuclear cell-recruiting chemokines uniquely from synovial fibroblasts, but not matched skin fibroblasts, via a PI 3-kinase signaling pathway. These data provide further evidence of the role of synovial fibroblasts in regulating the pattern and persistence of the inflammatory infiltrate in RA and suggest a new and important functional consequence of the observed high expression of galectin 3 in the rheumatoid synovium.

Galectin-2 suppresses contact allergy by inducing apoptosis in activated CD8+ T cells

Galectins, a family of structurally related beta-galactoside-binding proteins, are expressed by various cells of the immune systems and seem to be important for the regulation of immune responses and immune cell homeostasis. Since it has been demonstrated that galectin-2 regulates cell-mediated inflammatory bowel disease and colitis in mice, we intended to investigate the role of galectin-2 in inflammatory cutaneous T cell-mediated immune responses. To address this issue, groups of naive mice were sensitized to the contact allergen 2,4-dinitro-1-fluorobenzene and systemically treated with galectin-2 to analyze the effects of galectin-2 on contact allergy. Here we show that galectin-2 is expressed in murine skin and is up-regulated upon cutaneous inflammation. Interestingly, treatment of mice with galectin-2 significantly reduced the contact allergy response. This effect was long-lasting since rechallenge of galectin-2-treated mice after a 14-day interval still resulted in a decreased ear swelling. We were able to demonstrate that galectin-2 induced a reduction of MHC class I-restricted immune responses in the treated animals, which was mediated by the induction of apoptosis specifically in activated CD8(+) T cells. Additionally, we report that the galectin-2-binding protein CD29 is up-regulated on the surface of activated CD8(+) T cells compared with naive CD8(+) T cells or CD4(+) T cells, suggesting that increased galectin-2/CD29 signaling might be responsible for the proapoptotic effects of galectin-2 on activated CD8(+) T cells. Taken together, these data indicate that galectin-2 may represent a novel therapeutic alternative for the treatment of CD8-mediated inflammatory disorders such as contact allergy.

Turning 'sweet' on immunity: galectin-glycan interactions in immune tolerance and inflammation

The function of deciphering the biological information encoded by the glycome, which is the entire repertoire of complex sugar structures expressed by cells and tissues, is assigned in part to endogenous glycan-binding proteins or lectins. Galectins, a family of animal lectins that bind N-acetyllactosamine-containing glycans, have many roles in diverse immune cell processes, including those relevant to pathogen recognition, shaping the course of adaptive immune responses and fine-tuning the inflammatory response. How do galectins translate glycan-encoded information into tolerogenic or inflammatory cell programmes? An improved understanding of the mechanisms underlying these functions will provide further opportunities for developing new therapies based on the immunoregulatory properties of this multifaceted protein family.

Suppression of autoimmune diabetes by soluble galectin-1

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease that targets the beta-cells of the pancreas. We investigated the ability of soluble galectin-1 (gal-1), an endogenous lectin that promotes T cell apoptosis, to down-regulate the T cell response that destroys the pancreatic beta-cells. We demonstrated that in nonobese diabetic (NOD) mice, gal-1 therapy reduces significantly the amount of Th1 cells, augments the number of T cells secreting IL-4 or IL-10 specific for islet cell Ag, and causes peripheral deletion of beta-cell-reactive T cells. Administration of gal-1 prevented the onset of hyperglycemia in NOD mice at early and subclinical stages of T1D. Preventive gal-1 therapy shifted the composition of the insulitis into an infiltrate that did not invade the islets and that contained a significantly reduced number of Th1 cells and a higher percentage of CD4(+) T cells with content of IL-4, IL-5, or IL-10. The beneficial effects of gal-1 correlated with the ability of the lectin to trigger apoptosis of the T cell subsets that cause beta-cell damage while sparing naive T cells, Th2 lymphocytes, and regulatory T cells in NOD mice. Importantly, gal-1 reversed beta-cell autoimmunity and hyperglycemia in NOD mice with ongoing T1D. Because gal-1 therapy did not cause major side effects or beta-cell toxicity in NOD mice, the use of gal-1 to control beta-cell autoimmunity represents a novel alternative for treatment of subclinical or ongoing T1D.

Duodenal intraepithelial lymphocytes of children with cow milk allergy preferentially bind the glycan-binding protein galectin-3

A breakdown in intestinal homeostasis results in inflammatory bowel diseases including coeliac disease and allergy. Galectins, evolutionarily conserved beta-galactoside-binding proteins, can modulate immune-epithelial cell interactions by influencing immune cell fate and cytokine secretion. In this study we investigated the glycosylation signature, as well as the regulated expression of galectin-1 and -3 in human duodenal samples of allergic and non-allergic children. Whereas galectin-1 was predominantly localized in the epithelial compartment (epithelial cells and intraepithelial lymphocytes) and the underlying lamina propria (T cells, macrophages and plasma cells), galectin-3 was mainly expressed by crypt epithelial cells and macrophages in the lamina propria. Remarkably, expression of these galectins was not significantly altered in allergic versus non-allergic patients. Investigation of the glycophenotype of the duodenal inflammatory microenvironment revealed substantial alpha2-6-linked sialic acid bound to galactose in lamina propria plasma cells, macrophages and intraepithelial lymphocytes and significant levels of asialo core 1 O-glycans in CD68+ macrophages and enterocytes. Galectin-1 preferentially bound to neutrophils, plasma cells and enterocytes, while galectin-3 binding sites were mainly distributed on macrophages and intraepithelial lymphocytes. Notably, galectin-3, but not galectin-1 binding, was substantially increased in intraepithelial gut lymphocytes of allergic patients compared to non-allergic subjects, suggesting a potential role of galectin-3-glycan interactions in shaping epithelial-immune cell connections during allergic inflammatory processes.

Galectin-3 deficiency reduces the severity of experimental autoimmune encephalomyelitis

Galectin-3 (Gal-3) is a member of the beta-galactoside-binding lectin family and plays an important role in inflammation. However, the precise role of Gal-3 in autoimmune diseases remains obscure. We have investigated the functional role of Gal-3 in experimental autoimmune encephalomyelitis (EAE) following immunization with myelin oligodendrocyte glycoprotein (MOG)35-55 peptide. Gal-3 deficient (Gal-3-/-) mice developed significantly milder EAE and markedly reduced leukocyte infiltration in the CNS compared with similarly treated wild-type (WT) mice. Gal-3-/- mice also contained fewer monocytes and macrophages but more apoptotic cells in the CNS than did WT mice. Following Ag stimulation in vitro, lymph node cells from the immunized Gal-3-/- mice produced less IL-17 and IFN-gamma than did those of the WT mice. In contrast, Gal-3-/- mice produced more serum IL-10, IL-5, and IL-13 and contained higher frequency of Foxp3+ regulatory T cells in the CNS than did the WT mice. Furthermore, bone marrow-derived dendritic cells from Gal-3-/- mice produced more IL-10 in response to LPS or bacterial lipoprotein than did WT marrow-derived dendritic cells. Moreover, Gal-3-/- dendritic cells induced Ag-specific T cells to produce more IL-10, IL-5, and IL-12, but less IL-17, than did WT dendritic cells. Taken together, our data demonstrate that Gal-3 plays an important disease-exacerbating role in EAE through its multifunctional roles in preventing cell apoptosis and increasing IL-17 and IFN-gamma synthesis, but decreasing IL-10 production.

The immunological potential of galectin-1 and -3

A family of beta-galactosides-binding proteins, called galectins, have recently emerged as novel molecules with immunoregulatory functions. These proteins are expressed in both inflammatory and non-inflammatory cells including monocytes, macrophages, dendritic cells, mast cells, and B and T cells, giving a broad spectrum of involvement in the immune response. Galectins are uniquely capable of acting both intracellularly and extracellularly, affecting such processes as cell adhesion, signaling, proliferation, differentiation, and apoptosis. Different members of this family have been shown to modulate several pathological processes such as allergic reactions, autoimmunity, and tumor invasion. Therefore, understanding the role of galectins in achieving appropriate proliferative and effector responses to antigens will yield important insights to autoimmune diseases and delineate novel strategies for disease intervention.

Severe preeclampsia is characterized by increased placental expression of galectin-1

OBJECTIVE

Galectin-1 is a major anti-inflammatory protein expressed by the placenta and immune cells that can bias the character of inflammatory responses toward the Th2 type. Galectin-1 is expressed in immune privileged sites, it can facilitate immune tolerance and tumor immune escape, and it has been successfully used for the suppression of experimental autoimmune diseases as well as graft-versus-host disease in murine models. We propose that an abnormal immune response in some pregnancy complications may be associated with changes in placental expression of galectin-1. To test this hypothesis, we studied placental galectin-1 mRNA and protein expression and localization in women with preeclampsia (PE) and in those who delivered a small-for-gestational age (SGA) neonate.

STUDY DESIGN

This cross-sectional study included pregnant women matched for gestational age at delivery in the following groups: (1) severe PE (n = 10), (2) severe PE complicated with SGA (n = 10), (3) SGA without PE (n = 10), and (4) controls (n = 10). Galectin-1 mRNA and protein were localized in placentas by in situ hybridization and immunofluorescence microscopy. Galectin-1 mRNA expression was determined by quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR), and galectin-1 protein content by Western blot. Non-parametric statistics were used for analysis.

RESULT

(1) In normal term placentas, galectin-1 mRNA or immunofluorescence signals were detected in the trophoblasts, villous stromal cells, Hofbauer cells, endothelial cells of the villous blood vessels, and the villous stroma. (2) Placental galectin-1 mRNA expression was significantly higher in severe PE (with or without SGA) than in controls (1.47-fold, p = 0.004; 1.44-fold, p = 0.003, respectively) and in SGA (1.68-fold, p = 0.001; 1.64-fold, p = 0.001, respectively). (3) Trophoblasts in placentas of patients with severe PE had the most intense galectin-1 immunostaining.

CONCLUSIONS

(1) We report for the first time the placental expression and localization of galectin-1 mRNA and demonstrate that the protein is abundantly present in third trimester human placentas. (2) Placental galectin-1 expression is higher in severe PE than in normal pregnancy regardless of the presence of SGA. (3) However, it is not altered in SGA without PE. We propose that the increased placental expression of galectin-1 in patients with severe PE may represent a fetal response to an exaggerated systemic maternal inflammation; thus, galectin-1 may be implicated in maternal-fetal immune tolerance in humans.

Tumor-associated galectin-3 modulates the function of tumor-reactive T cells

T cells play an important role in cancer immunosurveillance and tumor destruction. However, tumor cells alter immune responses by modulating immune cells through antigen stimulation and immunoregulatory cytokines. A better understanding of the interplay between tumor cells and T cells might provide new strategies to enhance antitumor immunity. Through an antigen-screening approach using colorectal tumor-reactive T cells, we identified an HLA-DR11-restricted T-cell epitope encoded by KIAA0040 as well as MHC-unrestricted human galectin-3 (Gal-3) expressed by tumor cells. Although the biological function of KIAA0040 remains to be determined, we found that Gal-3 functioned as an immune regulator for direct T-cell activation and function. T-cell activation induced by Gal-3 resulted in T-cell apoptosis. We showed that a high level of expression of Gal-3 promoted tumor growth in vitro and in vivo. Using a mouse tumor model, we showed that delivery of high doses of Gal-3 inhibited tumor-reactive T cells and promoted tumor growth in mice receiving tumor-reactive CD8(+) T cells. These findings suggest that Gal-3 may function as an immune regulator to inhibit T-cell immune responses and promote tumor growth, thus providing a new mechanism for tumor immune tolerance.

Roles of galectins in inflammatory bowel disease

Protein/carbohydrate interactions through specific protein families termed lectin control essential biological processes. Galectins, a family of animal lectins defined by shared amino acid sequence with affinity for β-galactosides, appear to be functionally polyvalent in a wide range of biological activity. Recent studies have identified immunoregulatory roles of galectins in intestinal inflammatory disorders. Galectin-1 and galectin -2 contribute to the suppression of intestinal inflammation by the induction of apoptosis of activated T cells, whereas galectin-4 is involved in the exacerbation of this inflammation by specifically stimulating intestinal CD4+ T cells to produce IL-6. We review how different members of the galectins provide inhibitory or stimulatory signals to control intestinal immune response under intestinal inflammation.

Differential roles of galectin-1 and galectin-3 in regulating leukocyte viability and cytokine secretion

Galectin-1 (Gal-1) and galectin-3 (Gal-3) exhibit profound but unique immunomodulatory activities in animals but their molecular mechanisms are incompletely understood. Early studies suggested that Gal-1 inhibits leukocyte function by inducing apoptotic cell death and removal, but recent studies show that some galectins induce exposure of the common death signal phosphatidylserine (PS) independently of apoptosis. In this study, we report that Gal-3, but not Gal-1, induces both PS exposure and apoptosis in primary activated human T cells, whereas both Gal-1 and Gal-3 induce PS exposure in neutrophils in the absence of cell death. Gal-1 and Gal-3 bind differently to the surfaces of T cells and only Gal-3 mobilizes intracellular Ca2+ in these cells, although Gal-1 and Gal-3 bind their respective T cell ligands with similar affinities. Although Gal-1 does not alter T cell viability, it induces IL-10 production and attenuates IFN-gamma production in activated T cells, suggesting a mechanism for Gal-1-mediated immunosuppression in vivo. These studies demonstrate that Gal-1 and Gal-3 induce differential responses in T cells and neutrophils, and identify the first factor, Gal-3, capable of inducing PS exposure with or without accompanying apoptosis in different leukocytes, thus providing a possible mechanism for galectin-mediated immunomodulation in vivo.

Protein-glycan interactions in the control of innate and adaptive immune responses

The importance of protein glycosylation in the migration of immune cells throughout the body has been extensively appreciated. However, our awareness of the impact of glycosylation on the regulation of innate and adaptive immune responses is relatively new. An increasing number of studies reveal the relevance of glycosylation to pathogen recognition, to the modulation of the innate immune system and to the control of immune cell homeostasis and inflammation. Similarly important is the effect of glycan-containing 'information' in the development of autoimmune diseases and cancer. In this review, we provide an overview of these new directions and their impact in the field of glycoimmunology.

Galectins: structure, function and therapeutic potential

Galectins are a family of animal lectins that bind beta-galactosides. Outside the cell, galectins bind to cell-surface and extracellular matrix glycans and thereby affect a variety of cellular processes. However, galectins are also detectable in the cytosol and nucleus, and may influence cellular functions such as intracellular signalling pathways through protein-protein interactions with other cytoplasmic and nuclear proteins. Current research indicates that galectins play important roles in diverse physiological and pathological processes, including immune and inflammatory responses, tumour development and progression, neural degeneration, atherosclerosis, diabetes, and wound repair. Some of these have been discovered or confirmed by using genetically engineered mice deficient in a particular galectin. Thus, galectins may be a therapeutic target or employed as therapeutic agents for inflammatory diseases, cancers and several other diseases.

AP1-dependent galectin-1 expression delineates classical hodgkin and anaplastic large cell lymphomas from other lymphoid malignancies with shared molecular features

PURPOSE

Galectin-1 (Gal1) is an immunomodulatory glycan-binding protein regulated by an AP1-dependent enhancer in Hodgkin Reed-Sternberg cells. We recently found that Reed-Sternberg cell Gal1 promotes the immunosuppressive T-helper 2/T-regulatory cell-skewed microenvironment in classical Hodgkin lymphoma (cHL). We sought to investigate whether the coordinate expression of activated AP1 pathway components and Gal1 serves as a diagnostic signature of cHL. In addition, because there are common signaling and survival pathways in cHL and additional non-Hodgkin lymphomas, we also evaluated whether the AP1/Gal1 signature is shared by other molecularly or morphologically related lymphomas.

EXPERIMENTAL DESIGN

We evaluated 225 cases of primary cHL and non-Hodgkin lymphoma for evidence of a functional AP1/Gal1 signature by immunohistochemical techniques.

RESULTS

Gal1 is selectively expressed by malignant Reed-Sternberg cells in >90% of primary cHLs, and Gal1 expression is concordant with the activated AP1 component, c-Jun. In contrast, diffuse large B-cell lymphoma, primary mediastinal large B-cell lymphoma, and another Hodgkin-related entity, nodular lymphocyte-predominant Hodgkin lymphoma, do not express Gal1. However, anaplastic large cell lymphoma (ALCL), consistently expresses both Gal1 and its transcriptional regulator, c-Jun. The presence of activated c-Jun, indicative of functional AP1 activity, was confirmed by phospho-c-Jun immunostaining in cHL and ALCL.

CONCLUSIONS

These findings establish a functional AP1 signature that includes Gal1 expression in cHL and ALCL and suggests a common mechanism for tumor immunotolerance in these diseases. In addition, the combination of Gal1 and c-Jun serve as diagnostic biomarkers that delineate cHL and ALCL from other lymphomas with shared morphologic and/or molecular features.

The secretome of the filarial parasite, Brugia malayi: proteomic profile of adult excretory-secretory products

The secretome of a parasite in its definitive host can be considered to be its genome in trans, to the extent that secreted products encoded by the parasite fulfill their function in the host milieu. The 'extended phenotype' of the filarial parasite, Brugia malayi, is of particular interest because of the evidence that infection results in potent down-modulation of the host immune response. We collected B. malayi 'excretory-secretory' (BES) proteins from adult parasites and using a combination of shotgun LC-MS/MS and 2D gel electrophoresis, identified 80 B. malayi and two host proteins in BES, of which 31 (38%) were detectable in whole worm extract (BmA). Products which were enriched in BES relative to BmA included phosphatidylethanolamine-binding protein (PEB), leucyl aminopeptidase (LAP, homologue of ES-62 from the related filaria Acanthocheilonema viteae), N-acetylglucosaminyltransferase (GlcNAcT) and galectin-1, in addition to the previously described major surface glycoprotein, glutathione peroxidase (gp29, GPX-1) and the cytokine homologue macrophage migration inhibitory factor (MIF-1). One of the most abundant released proteins was triose phosphate isomerase (TPI), yet many other glycolytic enzymes (such as aldolase and GAPDH) were found only in the somatic extract. Among the more prominent novel products identified in BES were a set of 11 small transthyretin-like proteins, and three glutamine-rich-repeat mucin-like proteins. Notably, no evidence was found of any secreted protein corresponding to the genome of the Wolbachia endosymbiont present in B. malayi. Western blotting with anti-phosphorylcholine (PC) monoclonal antibody identified that GlcNAcT, and not the ES-62 homologue, is the major PC-bearing protein in BES, while probing with human filariasis sera showed preferential reactivity to galectin-1 and to processed forms of myotactin. Overall, this analysis demonstrates selective release of a suite of newly identified proteins not previously suspected to be involved at the host-parasite interface, and provides important new perspectives on the biology of the filarial parasite.

Immunosuppressive mechanisms in human tumors: why we still cannot cure cancer

Tumor cells often evoke specific immune responses that, however, fail to eliminate all the tumor cells. The development of cancer immunotherapies is, therefore, mostly focused on the generation of large numbers of activated anti-tumor effector cells by vaccination or adoptive T cell transfer. These developments are built on an ever-extended list of identified tumor-associated antigens and corresponding T cell epitopes, and a steady flow of reports from proof-of-principle animal model experiments demonstrating cure from disease by immune interventions. However, the promises have not translated into clinical successes for cancer patients. Even where tumor regression or complete responses were achieved there is usually relapse of the disease. Increasing numbers of reports over recent years highlight potential immunosuppressive mechanisms that act in tumors and systemically in cancer patients to block effective anti-tumor immune responses. They account in large parts for the failures of cancer immunotherapy and need to be overcome before progress can be expected. We review here the current state of the research on immunosuppressive networks in human cancer.

Tolerance signaling molecules and pregnancy: IDO, galectins, and the renaissance of regulatory T cells

PROBLEM

Is the concept of maternal tolerance preventing rejection of the semi-allogeneic 'fetal allograft' still valid?

METHOD OF STUDY

Compilation of expert reviews of literature and recent advances in research on indoleamine-2,3 dioxygenase (IDO), regulatory T cells and galectin-1.

RESULTS AND CONCLUSION

A role for IDO in pregnancy success remains speculative, but solid data exist to support a role for Treg cells, and for galectin-1 in induction and action of Treg cells. Just as several signals may need to be simultaneously present to induce Th1 cytokine-triggered abortions, more than 1 signal may need to be simultaneously present to prevent rejection and ensure success. Both complement and coagulation pathways appear necessary for embryo execution.

Functions of cell surface galectin-glycoprotein lattices

Programmed remodeling of cell surface glycans by the sequential action of specific glycosyltransferases can control biological processes by generating or masking ligands for endogenous lectins. Galectins, a family of animal lectins with affinity for beta-galactosides, can form multivalent complexes with cell surface glycoconjugates and deliver a variety of intracellular signals to modulate cell activation, differentiation, and survival. Recent efforts involving genetic or biochemical manipulation of O-glycosylation and N-glycosylation pathways, as well as blockade of the synthesis of endogenous galectins, have illuminated essential roles for galectin-glycoprotein lattices in the control of biological processes including receptor turnover and endocytosis, host-pathogen interactions, and immune cell activation and homeostasis.

An emerging role for galectins in tuning the immune response: lessons from experimental models of inflammatory disease, autoimmunity and cancer

Inflammation is a critical process for eliminating pathogens, but can lead to serious deleterious effects if left unchecked. Identifying the endogenous factors that control immune tolerance and inflammation is a key goal in the field of immunology. Galectins, a family of endogenous lectins with affinity for beta-galactoside-containing oligosaccharides, are expressed by several cells of the immune system and tissue-resident stromal cells. According to their architecture, this family of glycan-binding proteins is classified in those containing one-carbohydrate-recognition domain (CRD) (proto-type), those containing two-CRD joined by a linker non-lectin domain (tandem-repeat) and those that have one-CRD attached to an N-terminal peptide (chimera-type). Accumulating evidence indicates that galectins play critical regulatory roles in immune cell response and homeostasis. In this review, we summarize recent developments in our understanding of the galectins' roles within different immune cell compartments, and in the broader context of the inflammatory microenvironments. In particular we illustrate the immunoregulatory role of three representative members of each galectin subfamily: galectin-1, -3 and -9. This body of knowledge, documenting the coming of age of galectins as potential immunosuppressive agents or targets for anti-inflammatory drugs, represents a sound basis to further explore their potential as novel therapies for autoimmune diseases, chronic inflammation and cancer.

The AP1-dependent secretion of galectin-1 by Reed Sternberg cells fosters immune privilege in classical Hodgkin lymphoma

Classical Hodgkin lymphomas (cHLs) contain small numbers of neoplastic Reed-Sternberg (RS) cells within an extensive inflammatory infiltrate that includes abundant T helper (Th)-2 and T regulatory (Treg) cells. The skewed nature of the T cell infiltrate and the lack of an effective host antitumor immune response suggest that RS cells use potent mechanisms to evade immune attack. In a screen for T cell-inhibitory molecules in cHL, we found that RS cells selectively overexpressed the immunoregulatory glycan-binding protein, galectin-1 (Gal1), through an AP1-dependent enhancer. In cocultures of activated T cells and Hodgkin cell lines, RNAi-mediated blockade of RS cell Gal1 increased T cell viability and restored the Th1/Th2 balance. In contrast, Gal1 treatment of activated T cells favored the secretion of Th2 cytokines and the expansion of CD4+CD25high FOXP3+ Treg cells. These data directly implicate RS cell Gal1 in the development and maintenance of an immunosuppressive Th2/Treg-skewed microenvironment in cHL and provide the molecular basis for selective Gal1 expression in RS cells. Thus, Gal1 represents a potential therapeutic target for restoring immune surveillance in cHL.

Human CD4+CD25+ regulatory T cells: proteome analysis identifies galectin-10 as a novel marker essential for their anergy and suppressive function

CD4(+)CD25(+)Foxp3(+) regulatory T cells (CD25(+) Treg cells) direct the maintenance of immunological self-tolerance by active suppression of autoaggressive T-cell populations. However, the molecules mediating the anergic state and regulatory function of CD25(+) Treg cells are still elusive. Using differential proteomics, we identified galectin-10, a member of the lectin family, as constitutively expressed in human CD25(+) Treg cells, while they are nearly absent in resting and activated CD4(+) T cells. These data were confirmed on the mRNA and protein levels. Single-cell staining and flow cytometry showed a strictly intracellular expression of galectin-10 in CD25(+) Treg cells. Specific inhibition of galectin-10 restored the proliferative capacity of CD25(+) Treg cells and abrogated their suppressive function. Notably, first identified here as expressed in human T lymphocytes, galectin-10 is essential for the functional properties of CD25(+) Treg cells.

Galectin-1 mediated suppression of Epstein-Barr virus specific T-cell immunity in classic Hodgkin lymphoma

In Hodgkin lymphoma (HL), the malignant Hodgkin Reed-Sternberg cells interact with the host microenvironment to create an immunosuppressive network that protects the lymphoma from immune attack. These mechanisms are not fully understood. We examined the role of the immunomodulatory protein galectin-1 (Gal-1) on Epstein-Barr virus-specific CD8(+) T cell responses in HL. Initial studies indicated Gal-1 expression in all in vitro established Hodgkin Reed-Sternberg cell lines. In situ analysis revealed Gal-1 expression in 26 of 42 classic HL, whereas Gal-1 was uniformly negative in nodular lymphocyte predominant HL. Gal-1(hi) expression was associated with male gender, older patients, reduced CD8(+) T cell infiltration at the tumor site, and most importantly, an impaired latent membrane protein 1 and 2-specific CD8(+) T-cell responses. In vitro exposure to recombinant Gal-1 inhibited proliferation and interferon-gamma expression by Epstein-Barr virus-specific T cells. These observations provide an important link between the Gal-1-mediated immunomodulatory networks and loss of antigen-specific T-cell function in classic HL.

Dissecting the pathophysiologic role of endogenous lectins: Glycan-binding proteins with cytokine-like activity?

Several families of endogenous glycan-binding proteins have been implicated in a wide variety of immunological functions including first-line defence against pathogens, cell trafficking, and immune regulation. These include, among others, the C-type lectins (collectins, selectins, mannose receptor, and others), S-type lectins (galectins), I-type lectins (siglecs and others), P-type lectins (phosphomannosyl receptors), pentraxins, and tachylectins. This review will concentrate on the immunoregulatory roles of galectins (particularly galectin-1) and collectins (mannose-binding lectins and surfactant proteins) to illustrate the ability of endogenous glycan-binding proteins to act as cytokines, chemokines or growth factors, and thereby modulating innate and adaptive immune responses under physiological or pathological conditions. Understanding the pathophysiologic relevance of endogenous lectins in vivo will reveal novel targets for immunointervention during chronic infection, autoimmunity, transplantation and cancer.

Is the sugar always sweet in intestinal inflammation?

Immune responses are mediated mainly by protein/protein interactions. In addition, protein/carbohydrate (sugar) interactions through specific protein families termed lectin and chi-lectin are also involved in several immune and biological responses under not only the state of health but also inflammatory conditions. Interestingly, recent studies have identified unexpected roles of animal lectins (galectin-1 and galectin-4) and chi-lectin (chitinase 3-like-1) in intestinal inflammation. Galectin-1 contributes to the suppression of intestinal inflammation by the induction of effector T cell apoptosis. In contrast, galectin-4 is involved in the exacerbation of this inflammation by specifically stimulating intestinal CD4+ T cells to produce IL-6. CHI3L1 enhances the host/microbial interaction that leads to the exacerbation of intestinal inflammation. In this review, we discuss a novel aspect of lectin/carbohydrate interactions in intestinal inflammation.

A Novel Function for Galectin-1 at the Crossroad of Innate and Adaptive Immunity: Galectin-1 Regulates Monocyte/Macrophage Physiology through a Nonapoptotic ERK-Dependent Pathway

Several environmental factors can differentially regulate monocyte and macrophage response patterns, resulting in the display of distinct functional phenotypes. Galectin-1, an endogenous lectin found at peripheral lymphoid organs and inflammatory sites, has shown immunoregulatory activity in vivo in experimental models of autoimmunity and cancer. Whereas compelling evidence has been accumulated regarding the effects of galectin-1 on T cell fate, limited information is available on how galectin-1 may impact other immune cell types. In the present study, we report a novel role for galectin-1 in the regulation of monocyte and macrophage physiology. Treatment with galectin-1 in vitro differentially regulates constitutive and inducible FcgammaRI expression on human monocytes and FcgammaRI-dependent phagocytosis. In addition, galectin-1 inhibits IFN-gamma-induced MHC class II (MHC-II) expression and MHC-II-dependent Ag presentation in a dose-dependent manner. These regulatory effects were also evident in mouse macrophages recruited in response to inflammatory stimuli following treatment with recombinant galectin-1 and further confirmed in galectin-1-deficient mice. Investigation of the mechanisms involved in these functions showed that galectin-1 does not affect survival of human monocytes, but rather influences FcgammaRI- and MHC-II-dependent functions through active mechanisms involving modulation of an ERK1/2-dependent pathway. Our results provide evidence of a novel unrecognized role for galectin-1 in the control of monocyte/macrophage physiology with potential implications at the crossroad of innate and adaptive immunity.