Glycobiology of immune responses

Determining the monosaccharides of the sea urchin (Paracentrotus lividus) coelomocytes via the CapLC-ESI-MS/MS system and the lectin histochemistry

The essential mechanism within immune systems is the recognition of pathogens and parasites by the immune system cells, which attach to their targets and destroy them. Glycans are fundamental macromolecular components of all cells, and are important in the vertebrate immunity. But, glycans have been investigated rarely in coelomocytes of echinoids. Hence, the aim of this study is to determine the monosaccharides which form glycan chains on the sea urchin immune system cells, coelomocytes, via analytical and lectin histochemistry methods. The study material is the coelomocytes obtained from adult sea urchin Paracentrotus lividus. In order to analyze the monosaccharides with the Capillary Liquid Chromatography Electrospray Ionization Tandem Mass Spectrometry (CapLC-ESI-MS/MS) system, the samples underwent hydrolysation, reacetylation and derivatization steps. In order to determine the monosaccharides with the lectin histochemistry, the cells were incubated with fluorescein isothiocyanate (FITC) conjugated PNA, HPA, WGA-suc, WGA, and PSL lectins and then photographed with the fluorescence microscope. As a result of the CapLC-ESI-MS/MS analysis; mannose, ribose, N-acetylglucosamine, glucose, N-acetylgalactosamine, galactose, arabinose, xylose and fucose monosaccharides were detected. A peak area calculation analysis revealed the most prevalent saccharides as glucose, galactose and fucose, respectively. Lectin histochemistry came out with higher intensity emission signals obtained from the FITC-conjugated lectin WGA, which is specific to N-acetylglucosamine and sialic acid in comparison to the emission obtained from the sialic acid unspecific WGA-suc lectin. This finding indicates the existence of sialic acid within coelomocytes. Fluorescent emissions from other lectins were detected at lower levels. Determination of the monosaccharides which form glycan chains of the sea urchin coelomocytes and elucidating their similarities among other invertebrate and vertebrate systems is vital in terms of understanding the uncovered complex features of the immune systems of higher vertebrates.

Recent advances in engineering yeast for pharmaceutical protein production

Currently available systems and synthetic biology tools can be applied to yeast engineering for improved biopharmaceutical protein production.

Functional impact of tumor-specific N-linked glycan changes in breast and ovarian cancers

Changes in glycosylation have been implicated in various human diseases, including cancer. Research over the past few decades has produced significant findings that illustrate the importance of cancer-specific alterations in glycosylation in the regulation of tumor formation and metastasis. The identification of glycan-based biomarkers and strategies targeting specific glycan epitopes on the tumor cell surface has become one of the widely pursued research areas. In this chapter, we will summarize and provide perspective on available knowledge about the functional roles that glycan structures play in the development and progression of the gynecological cancers, breast and ovarian, with a specific focus on N-linked glycans. A better understanding of the functional roles for glycans in cancer will drive future innovations for diagnostics and therapeutics.

Differential expression of collectins in human placenta and role in inflammation during spontaneous labor

Collectins, collagen-containing Ca²⁺ dependent C-type lectins and a class of secretory proteins including SP-A, SP-D and MBL, are integral to immunomodulation and innate immune defense. In the present study, we aimed to investigate their placental transcript synthesis, labor associated differential expression and localization at feto-maternal interface, and their functional implication in spontaneous labor. The study involved using feto-maternal interface (placental/decidual tissues) from two groups of healthy pregnant women at term (≥37 weeks of gestation), undergoing either elective C-section with no labor (‘NLc’ group, n = 5), or normal vaginal delivery with spontaneous labor (‘SLv’ group, n = 5). The immune function of SP-D, on term placental explants, was analyzed for cytokine profile using multiplexed cytokine array. SP-A, SP-D and MBL transcripts were observed in the term placenta. The ‘SLv’ group showed significant up-regulation of SP-D (p = 0.001), and down-regulation of SP-A (p = 0.005), transcripts and protein compared to the ‘NLc’ group. Significant increase in 43 kDa and 50 kDa SP-D forms in placental and decidual tissues was associated with the spontaneous labor (p<0.05). In addition, the MMP-9-cleaved form of SP-D (25 kDa) was significantly higher in the placentae of ‘SLv’ group compared to the ‘NLc’ group (p = 0.002). Labor associated cytokines IL-1α, IL-1β, IL-6, IL-8, IL-10, TNF-α and MCP-1 showed significant increase (p<0.05) in a dose dependent manner in the placental explants treated with nSP-D and rhSP-D. In conclusion, the study emphasizes that SP-A and SP-D proteins associate with the spontaneous labor and SP-D plausibly contributes to the pro-inflammatory immune milieu of feto-maternal tissues.

Differential site accessibility mechanistically explains subcellular-specific N-glycosylation determinants

Glycoproteins perform extra- and intracellular functions in innate and adaptive immunity by lectin-based interactions to exposed glyco-determinants. Herein, we document and mechanistically explain the formation of subcellular-specific N-glycosylation determinants on glycoproteins trafficking through the shared biosynthetic machinery of human cells. LC-MS/MS-based quantitative glycomics showed that the secreted glycoproteins of eight human breast epithelial cells displaying diverse geno- and phenotypes consistently displayed more processed, primarily complex type, N-glycans than the high-mannose-rich microsomal glycoproteins. Detailed subcellular glycome profiling of proteins derived from three breast cell lines (MCF7/MDA468/MCF10A) demonstrated that secreted glycoproteins displayed significantly more α-sialylation and α1,6-fucosylation, but less α-mannosylation, than both the intermediately glycan-processed cell-surface glycoproteomes and the under-processed microsomal glycoproteomes. Subcellular proteomics and gene ontology revealed substantial presence of endoplasmic reticulum resident glycoproteins in the microsomes and confirmed significant enrichment of secreted and cell-surface glycoproteins in the respective subcellular fractions. The solvent accessibility of the glycosylation sites on maturely folded proteins of the 100 most abundant putative N-glycoproteins observed uniquely in the three subcellular glycoproteomes correlated with the glycan type processing thereby mechanistically explaining the formation of subcellular-specific N-glycosylation. In conclusion, human cells have developed mechanisms to simultaneously and reproducibly generate subcellular-specific N-glycosylation using a shared biosynthetic machinery. This aspect of protein-specific glycosylation is important for structural and functional glycobiology and discussed here in the context of the spatio-temporal interaction of glyco-determinants with lectins central to infection and immunity.

A role for the TIM-3/GAL-9/BAT3 pathway in determining the clinical phenotype of multiple sclerosis

T-cell immunoglobulin and mucin domain 3 (Tim-3) ligates galectin-9 (Gal-9); this process, resulting in the inhibition of Th1 responses and in the apoptosis of antigen-specific cells, is hampered by binding of the molecular adaptor human leukocyte antigen B (HLA-B)-associated transcript 3 (Bat3) to the intracellular tail of Tim-3. Apoptosis of myelin basic protein (MBP)-specific T lymphocytes correlates with reduced rates of disease progression in multiple sclerosis (MS). We extensively analyzed the Tim-3/Gal-9/Bat3 pathway in 87 patients with a diagnosis of stable relapsing-remitting MS (RRMS), primary progressive MS (PPMS), or benign MS (BEMS), as well as in 40 healthy control (HC) subjects. Results showed that MBP-specific CD4(+)Tim-3(+), CD4(+)/Gal-9(+), and CD4(+)/Tim-3(+)/AV(+) (apoptotic) T lymphocytes were augmented in the BEMS group, whereas CD4(+)/Bat3(+) and CD8(+)/Bat3(+) T lymphocytes were increased and CD4(+)/Tim-3(+)/AV(+) T cells were reduced in the PPMS group (>2 fold and P<0.05 in all cases). Blocking the Tim-3/Gal-9 interaction with specific mAb reduced T-lymphocyte apoptosis and augmented production of IFNγ and IL-17 in the BEMS, RRMS, and HC groups, but not in the PPMS group. The Tim-3/Gal-9 interaction favors apoptosis of MBP-specific T lymphocytes in BEMS; this process is reduced in PPMS by the up-regulation of Bat3. Therapeutic interventions aimed at silencing Bat3 could be beneficial in MS.

Biopharmaceutical discovery and production in yeast

The selection of an expression platform for recombinant biopharmaceuticals is often centered upon suitable product titers and critical quality attributes, including post-translational modifications. Although notable differences between microbial, yeast, plant, and mammalian host systems exist, recent advances have greatly mitigated any inherent liabilities of yeasts. Yeast expression platforms are important to both the supply of marketed biopharmaceuticals and the pipelines of novel therapeutics. In this review, recent advances in yeast-based expression of biopharmaceuticals will be discussed. The advantages of using glycoengineered yeast as a production host and in the discovery space will be illustrated. These advancements, in turn, are transforming yeast platforms from simple production systems to key technological assets in the discovery and selection of biopharmaceutical lead candidates.

Malignant T cells secrete galectins and induce epidermal hyperproliferation and disorganized stratification in a skin model of cutaneous T-cell lymphoma

Cutaneous T-cell lymphomas (CTCLs) are the most common primary skin lymphomas, which are characterized by an accumulation of malignant T cells in the skin. The early lesion resembles both clinically and histologically benign inflammatory disorders and also presents with hyperproliferative epidermis and T-cell infiltration. Despite considerable progress in understanding the molecular mechanisms involved in the malignant transformation of T cells, the causes of the morphological and histopathological features of the disease are largely unknown. We used an organotypic model of CTCL to show that malignant T cells through the secretion of galectin-1 and -3 stimulate vigorous growth of keratinocytes. In parallel, malignant T cells induce disorganized keratinocyte stratification, resembling the early hyperproliferative stage of CTCL. We also observed a loss of attachment between the epithelial and mesenchymal compartments. In addition, hyperproliferation was followed by a downregulation of differentiation markers, such as keratin 10 and involucrin, and a decrease in barrier formation. In conclusion, we provide evidence that malignant T cells orchestrate the histopathological epidermal changes seen in CTCL.

Direct evidence for the presence of human milk oligosaccharides in the circulation of breastfed infants

Background

It has been hypothesized that human milk oligosaccharides (HMOs) confer systemic health benefits to breastfed infants; however, plausible mechanisms for some effects, such as systemic immunomodulation, require HMOs to access the bloodstream of the developing infant. While small concentrations of HMOs have been detected in the urine of breastfed infants there are no published studies of these oligosaccharides accessing the plasma compartment of breastfed infants. Here we determined the relative fractions of several ingested HMOs in infant urine and plasma. Plasma from formula-fed infants was used as a control.

Methods

Using gas chromatography/mass spectrometry (GC/MS), liquid chromatography/mass spectrometry/tandem mass spectrometry (LC/MS/MS), and high performance liquid chromatography (HPLC), we analyzed the urine and plasma from 17 healthy formula-fed infants and 16 healthy breast-fed infants (and the milk from their mothers).

Results

Multiple HMOs were detected in the urine and plasma of breastfed infants, but not in formula-fed infants. Levels of 2′-fucosyllactose (2′FL), 3FL and lacto-N-neotetraose (LNnT) in both plasma (r = 0.98, p<0.001; r = 0.75, p = 0.002; r = 0.71, p = 0.004) and urine (r = 0.81, p<0.001; r = 0.56, p = 0.026; NS) correlated significantly with concentrations in the corresponding breast milk. The relative fractions of HMOs were low, 0.1% of milk levels for plasma and 4% of milk levels for urine. Within the breastfed cohort, there were significant differences between secretor and nonsecretor groups in levels of several fucosylated HMOs.

Conclusion

At least some ingested HMOs are absorbed intact into the circulation and excreted in the urine and their concentrations in these fluids correlate with levels of the corresponding mother's milk. While relative fractions of absorbed HMOs were low, these levels have been shown to have biological effects in vitro, and could explain some of the postulated benefits of human milk.

Contrasting Roles of the Apoplastic Aspartyl Protease APOPLASTIC, ENHANCED DISEASE SUSCEPTIBILITY1-DEPENDENT1 and LEGUME LECTIN-LIKE PROTEIN1 in Arabidopsis Systemic Acquired Resistance

Systemic acquired resistance (SAR) is an inducible immune response that depends on ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1). Here, we show that Arabidopsis (Arabidopsis thaliana) EDS1 is required for both SAR signal generation in primary infected leaves and SAR signal perception in systemic uninfected tissues. In contrast to SAR signal generation, local resistance remains intact in eds1 mutant plants in response to Pseudomonas syringae delivering the effector protein AvrRpm1. We utilized the SAR-specific phenotype of the eds1 mutant to identify new SAR regulatory proteins in plants conditionally expressing AvrRpm1. Comparative proteomic analysis of apoplast-enriched extracts from AvrRpm1-expressing wild-type and eds1 mutant plants led to the identification of 12 APOPLASTIC, EDS1-DEPENDENT (AED) proteins. The genes encoding AED1, a predicted aspartyl protease, and another AED, LEGUME LECTIN-LIKE PROTEIN1 (LLP1), were induced locally and systemically during SAR signaling and locally by salicylic acid (SA) or its functional analog, benzo 1,2,3-thiadiazole-7-carbothioic acid S-methyl ester. Because conditional overaccumulation of AED1-hemagglutinin inhibited SA-induced resistance and SAR but not local resistance, the data suggest that AED1 is part of a homeostatic feedback mechanism regulating systemic immunity. In llp1 mutant plants, SAR was compromised, whereas the local resistance that is normally associated with EDS1 and SA as well as responses to exogenous SA appeared largely unaffected. Together, these data indicate that LLP1 promotes systemic rather than local immunity, possibly in parallel with SA. Our analysis reveals new positive and negative components of SAR and reinforces the notion that SAR represents a distinct phase of plant immunity beyond local resistance.

Significance of sugar chain recognition by galectins and its involvement in disease-associated glycosylation

Galectins are β-galactoside-binding lectins that participate in a wide range of biological processes. Galectins are distributed both inside and outside cells and are believed to have roles in both intra- and extracellular milieus. One of the well-recognized functions of galectins is stabilization of glycoproteins on the cell surface, thereby promoting stable signal transduction and transport of substances such as glucose. Glycoprotein-associated diseases, including congenital disorder of glycosylation (CDG, previously called carbohydrate-deficient glycoprotein syndrome), comprise a disease family established only in the last decade. Although numerous in vitro glycobiology studies have been performed, including investigation of glycan-galectin interactions and of galectin action in cultured cells, a few in vivo studies have investigated molecular mechanisms of galectin actions in animal models. Both in vitro and in vivo studies are needed in order to better determine the biological significance of sugar chain recognition. Hitherto, some reports have focused on the role of impaired sugar chain recognition and galectin function in the development of diverse diseases, including rheumatoid arthritis, diabetes mellitus, colitis, and cancer. We recently focused on the function of galectins in immunity and embryogenesis, and in this review we summarize the diseases related to disorders of sugar chain-galectin interaction and discuss the role of galectins as potential risk factors for some congenital and acquired diseases. These diseases are disorders of immunity, metabolism, and cell differentiation. This approach to understanding the significance of sugar chain recognition by galectins may open up a new field into the nature of glycoprotein-related diseases, including CDG.

Targeting DNGR-1 (CLEC9A) with antibody/MUC1 peptide conjugates as a vaccine for carcinomas

DCs are the most potent APCs and are the focus of many immunotherapeutic approaches for the treatment of cancer, although most of these approaches require the ex vivo generation and pulsing of DCs. We have targeted a subset of DCs in vivo using an Ab to DNGR-1, a C-type lectin dedicated to the cross-presentation of Ag expressed by subsets of DCs. HLA-A2 epitopes from the tumour-associated Ag, MUC1, were coupled to the anti-DNGR-1 Ab, and their efficacy in generating a Th1-cell response and inhibiting tumour growth was evaluated in a clinically relevant double transgenic mouse model expressing human MUC1 and A2K/b. Using this strategy, we demonstrate that an effective immune response to MUC1 can be generated, which results in a significant delay in the growth of MUC1-expressing tumours in both prophylactic and therapeutic settings. In addition, we also show, using PBMCs isolated from healthy volunteer blood, that target an MUC1 HLA-A2 epitope to human DNGR-1 in vitro can induce an MUC1-specific CD8⁺-T-cell response, which confirms the relevance of our in vivo murine results in the human setting.

Cellular heterogeneity profiling by hyaluronan probes reveals an invasive but slow-growing breast tumor subset

Tumor heterogeneity confounds cancer diagnosis and the outcome of therapy, necessitating analysis of tumor cell subsets within the tumor mass. Elevated expression of hyaluronan (HA) and HA receptors, receptor for HA-mediated motility (RHAMM)/HA-mediated motility receptor and cluster designation 44 (CD44), in breast tumors correlates with poor outcome. We hypothesized that a probe for detecting HA-HA receptor interactions may reveal breast cancer (BCa) cell heterogeneity relevant to tumor progression. A fluorescent HA (F-HA) probe containing a mixture of polymer sizes typical of tumor microenvironments (10-480 kDa), multiplexed profiling, and flow cytometry were used to monitor HA binding to BCa cell lines of different molecular subtypes. Formulae were developed to quantify binding heterogeneity and to measure invasion in vivo. Two subsets exhibiting differential binding (HA(-/low) vs. HA(high)) were isolated and characterized for morphology, growth, and invasion in culture and as xenografts in vivo. F-HA-binding amounts and degree of heterogeneity varied with BCa subtype, were highest in the malignant basal-like cell lines, and decreased upon reversion to a nonmalignant phenotype. Binding amounts correlated with CD44 and RHAMM displayed but binding heterogeneity appeared to arise from a differential ability of HA receptor-positive subpopulations to interact with F-HA. HA(high) subpopulations exhibited significantly higher local invasion and lung micrometastases but, unexpectedly, lower proliferation than either unsorted parental cells or the HA(-/low) subpopulation. Querying F-HA binding to aggressive tumor cells reveals a previously undetected form of heterogeneity that predicts invasive/metastatic behavior and that may aid both early identification of cancer patients susceptible to metastasis, and detection/therapy of invasive BCa subpopulations.

Hypomorphic homozygous mutations in phosphoglucomutase 3 (PGM3) impair immunity and increase serum IgE levels

BACKGROUND

Recurrent bacterial and fungal infections, eczema, and increased serum IgE levels characterize patients with the hyper-IgE syndrome (HIES). Known genetic causes for HIES are mutations in signal transducer and activator of transcription 3 (STAT3) and dedicator of cytokinesis 8 (DOCK8), which are involved in signal transduction pathways. However, glycosylation defects have not been described in patients with HIES. One crucial enzyme in the glycosylation pathway is phosphoglucomutase 3 (PGM3), which catalyzes a key step in the synthesis of uridine diphosphate N-acetylglucosamine, which is required for the biosynthesis of N-glycans.

OBJECTIVE

We sought to elucidate the genetic cause in patients with HIES who do not carry mutations in STAT3 or DOCK8.

METHODS

After establishing a linkage interval by means of SNPchip genotyping and homozygosity mapping in 2 families with HIES from Tunisia, mutational analysis was performed with selector-based, high-throughput sequencing. Protein expression was analyzed by means of Western blotting, and glycosylation was profiled by using mass spectrometry.

RESULTS

Mutational analysis of candidate genes in an 11.9-Mb linkage region on chromosome 6 shared by 2 multiplex families identified 2 homozygous mutations in PGM3 that segregated with disease status and followed recessive inheritance. The mutations predict amino acid changes in PGM3 (p.Glu340del and p.Leu83Ser). A third homozygous mutation (p.Asp502Tyr) and the p.Leu83Ser variant were identified in 2 other affected families, respectively. These hypomorphic mutations have an effect on the biosynthetic reactions involving uridine diphosphate N-acetylglucosamine. Glycomic analysis revealed an aberrant glycosylation pattern in leukocytes demonstrated by a reduced level of tri-antennary and tetra-antennary N-glycans. T-cell proliferation and differentiation were impaired in patients. Most patients had developmental delay, and many had psychomotor retardation.

CONCLUSION

Impairment of PGM3 function leads to a novel primary (inborn) error of development and immunity because biallelic hypomorphic mutations are associated with impaired glycosylation and a hyper-IgE-like phenotype.

Increased sensitivity of Apolipoprotein E knockout mice to swainsonine dependent immunomodulation

The mechanisms that mediate accelerated atherosclerosis in autoimmune diseases remain unclear. One common mechanism that has been documented in autoimmune diseases and atherosclerosis is formation of hypoglycosyalted N-glycans on the cell surface. In this study we tested the effects of swainsonine, a class II α-mannosidase inhibitor which results in formation of hypoglycosylated N-glycans, on atherogenesis and immune cell dynamics in the atheroprone and hypercholesterolemic ApoE -/- mouse. Wild type or ApoE-/- mice (8 weeks of age) were fed a normal chow diet and administered swainsonine via the drinking water for 8 weeks at which time, atherosclerosis, and systemic markers of markers of inflammation were evaluated. Interestingly, no change in the rate of atherosclerosis development was observed in ApoE -/- mice treated with swainsonine. However, swainsonine significantly increased the number of peripheral blood leukocytes in ApoE -/- mice, with trends toward similar increases in swainsonine treated wild type mice noted. Assessment of leukocyte subsets using specific markers of all major blood lineages indicated that the increase in circulating leukocytes was due to the elevated number of progenitor cells. Consistent with swainsonine having a greater effect in ApoE -/- vs. wild type mice, increases in circulating inflammatory markers (IgA, IgG and chemokines) were observed in the former. Collectively, these data demonstrate that predisposition of ApoE -/- mice to vascular disease is associated with sensitization to the immunomodulatory effects of swainsonine and indicate that changes in N-glycans may provide a mechanism linking autoimmunity to atherogenesis.

Nicotine promotes apoptosis resistance of breast cancer cells and enrichment of side population cells with cancer stem cell-like properties via a signaling cascade involving galectin-3, α9 nicotinic acetylcholine receptor and STAT3

Nicotine, a main addictive compound in tobacco smoke, has been linked to promotion and progression of lung, head and neck, pancreatic, and breast cancers, but the detailed mechanisms of cancer progression remain elusive. Here, we show that nicotine induces the expression of galectin-3 (an anti-apoptotic β-galactoside-binding lectin) in breast cancer cell line and in primary tumors from breast cancer patients. Nicotine-induced up regulation of galectin-3 is due to an increased expression of α9 isoform of nicotinic acetylcholine receptor (α9nAChR), which activates transcription factor STAT3 that in turn, physically binds to galectin-3 (LGALS3) promoter and induces transcription of galectin-3. Intracellular galectin-3 increased mitochondrial integrity and suppressed chemotherapeutic-induced apoptosis of breast cancer cell. Moreover, nicotine-induced enrichment of side population cells with cancer stem cell-like properties was modulated by galectin-3 expression and could be significantly reduced by transient knock down of LGALS3 and its upstream signaling molecules STAT3 and α9nAChR. Thus, galectin-3 or its upstream signaling molecule STAT3 or α9nAChR could be a potential target to prevent nicotine-induced chemoresistance in breast cancer.

A shrimp C-type lectin inhibits proliferation of the hemolymph microbiota by maintaining the expression of antimicrobial peptides

Some aquatic invertebrates such as shrimp contain low albeit stable numbers of bacteria in the circulating hemolymph. The proliferation of this hemolymph microbiota in such a nutrient-rich environment is tightly controlled in healthy animals, but the mechanisms responsible had remained elusive. In the present study, we report a C-type lectin (MjHeCL) from the kuruma shrimp (Marsupenaeus japonicus) that participates in restraining the hemolymph microbiota. Although the expression of MjHeCL did not seem to be modulated by bacterial challenge, the down-regulation of its expression by RNA interference led to proliferation of the hemolymph microbiota, ultimately resulting in shrimp death. This phenotype was rescued by the injection of recombinant MjHeCL, which restored the healthy status of the knockdown shrimp. A mechanistic analysis revealed that MjHeCL inhibited bacterial proliferation by modulating the expression of antimicrobial peptides. The key function of MjHeCL in the shrimp immune homeostasis might be related to its broader recognition spectrum of the hemolymph microbiota components than other lectins. Our study demonstrates the role of MjHeCL in maintaining the healthy status of shrimp and provides new insight into the biological significance of C-type lectins, a diversified and abundant lectin family in invertebrate species.

Biological evaluation of multivalent lewis X-MGL-1 interactions

Myeloid C-type lectin receptors (CLRs) expressed by antigen-presenting cells are pattern-recognition receptors involved in the recognition of pathogens as well as of self-antigens. The interaction of carbohydrate ligands with a CLR can trigger immune responses. Although several CLR ligands are known, there is limited insight into CLR targeting by carbohydrate ligands. The weak affinity of lectin-carbohydrate interactions often renders multivalent carbohydrate presentation necessary. Here, we have analyzed the impact of multivalent presentation of the trisaccharide Lewis X (Le(X) ) epitope on its interaction with the CLR macrophage galactose-type lectin-1 (MGL-1). Glycan arrays, including N-glycan structures with terminal Le(X) , were prepared by enzymatic extension of immobilized synthetic core structures with two recombinant glycosyltransferases. Incubation of arrays with an MGL-1-hFc fusion protein showed up to tenfold increased binding to multiantennary N-glycans displaying Le(X) structures, compared to monovalent Le(X) trisaccharide. Multivalent presentation of Le(X) on the model antigen ovalbumin (OVA) led to increased cytokine production in a dendritic cell /T cell coculture system. Furthermore, immunization of mice with Le(X) -OVA conjugates modulated cytokine production and the humoral response, compared to OVA alone. This study provides insights into how multivalent carbohydrate-lectin interactions can be exploited to modulate immune responses.

Glycoproteomic analysis identifies human glycoproteins secreted from HIV latently infected T cells and reveals their presence in HIV+ plasma

Glycoproteins secreted into plasma from T cells infected with human immunodeficiency virus (HIV) latent infection may provide insight into understanding the host response to HIV infection in vivo. Glycoproteomics, which evaluates the level of the glycoproteome, remains a novel approach to study this host response to HIV. In order to identify human glycoproteins secreted from T cells with latent HIV infection, the medium from cultured HIV replication-competent T cells was compared with the medium from cultured parental A3.01 cells via solid phase extraction of glycopeptides (SPEG) and high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Using these methods, 59 human glycoproteins were identified as having significantly different abundance levels between the media from these two cell lines. The relevance of these 59 proteins to HIV infection in vivo was assessed in plasma from HIV+ and HIV- subjects. Comparison between T cell and plasma revealed that six glycoproteins (galectin-3-binding protein, L-selectin, neogenin, adenosine deaminase CECR1, ICOS ligand and phospholipid transfer protein) were significantly elevated in the HIV+ T cells and plasma studies. These findings suggest that the response of T cells harboring latent HIV infection contributed, in part, to the glycoprotein changes in HIV+ plasma. These proteins, once validated, could provide insight into host-HIV interaction.

Altered tumor-cell glycosylation promotes metastasis

Malignant transformation of cells is associated with aberrant glycosylation presented on the cell-surface. Commonly observed changes in glycan structures during malignancy encompass aberrant expression and glycosylation of mucins; abnormal branching of N-glycans; and increased presence of sialic acid on proteins and glycolipids. Accumulating evidence supports the notion that the presence of certain glycan structures correlates with cancer progression by affecting tumor-cell invasiveness, ability to disseminate through the blood circulation and to metastasize in distant organs. During metastasis tumor-cell-derived glycans enable binding to cells in their microenvironment including endothelium and blood constituents through glycan-binding receptors – lectins. In this review, we will discuss current concepts how tumor-cell-derived glycans contribute to metastasis with the focus on three types of lectins: siglecs, galectins, and selectins. Siglecs are present on virtually all hematopoietic cells and usually negatively regulate immune responses. Galectins are mostly expressed by tumor cells and support tumor-cell survival. Selectins are vascular adhesion receptors that promote tumor-cell dissemination. All lectins facilitate interactions within the tumor microenvironment and thereby promote cancer progression. The identification of mechanisms how tumor glycans contribute to metastasis may help to improve diagnosis, prognosis, and aid to develop clinical strategies to prevent metastasis.

Dysregulation of T cell receptor N-glycosylation: a molecular mechanism involved in ulcerative colitis

The incidence of inflammatory bowel disease is increasing worldwide and the underlying molecular mechanisms are far from being fully elucidated. Herein, we evaluated the role of N-glycosylation dysregulation in T cells as a key mechanism in the ulcerative colitis (UC) pathogenesis. The evaluation of the branched N-glycosylation levels and profile of intestinal T cell receptor (TCR) were assessed in colonic biopsies from UC patients and healthy controls. Expression alterations of the glycosyltransferase gene MGAT5 were also evaluated. We demonstrated that UC patients exhibit a dysregulation of TCR branched N-glycosylation on lamina propria T lymphocytes. Patients with severe UC showed the most pronounced defect on N-glycan branching in T cells. Moreover, UC patients showed a significant reduction of MGAT5 gene transcription in T lymphocytes. In this study, we disclose for the first time that a deficiency in branched N-glycosylation on TCR due to a reduced MGAT5 gene expression is a new molecular mechanism underlying UC pathogenesis, being a potential novel biomarker with promising clinical and therapeutic applications.

Conference report: "Functional Glycomics in HIV Type 1 Vaccine Design" workshop report, Bethesda, Maryland, April 30-May 1, 2012

A vital part of the renewed hope for a vaccine against the human immunodeficiency virus (HIV-1) is based on recent studies that have highlighted major sites of HIV-1 vulnerability that could be effectively targeted by a preventive vaccine. One of these potential vulnerabilities includes the dense cluster of carbohydrates surrounding HIV-1's envelope glycoproteins gp120 and gp41, typically referred to as the "glycan shield." Recent data from several laboratories have shown that glycans on the HIV-1 envelope form key epitopes for broadly neutralizing antibodies (bNAb). Moreover, HIV-1 envelope glycans play an important role in viral transmission, antigenicity, and immunogenicity. The recent availability of novel tools and technologies has now allowed investigators to leverage glycomic structure-function relationships in the design of candidate HIV-1 vaccines. Additionally, glycans modulate the immune response, playing an essential role in Fc receptor and complement activity. To promote cross-disciplinary collaboration and promote synergistic HIV-1- glycomics research, the National Institutes of Health (NIH) cosponsored and convened a 1.5-day workshop entitled "Functional Glycomics in HIV-1 Vaccine Design." The meeting focused on the role of glycan interactions with neutralizing antibodies, the influence of immunoglobulin G (IgG) Fc receptor glycosylation, newly available glycomics technologies, and how new information on the role of glycans could be applied in HIV-1 immunogen design strategies. This report summarizes the discussions of this workshop.

Select human milk oligosaccharides directly modulate peripheral blood mononuclear cells isolated from 10-d-old pigs

Infant formulas lack the complex mixture of oligosaccharides found in human milk. These human milk oligosaccharides (HMO) may be pivotal to the development of the neonatal immune system. Few comprehensive analyses of the effects of HMO on immune cells from neonates have been undertaken. Herein, the direct effects of HMO on immune cells were analysed ex vivo. Peripheral blood mononuclear cells (PBMC) isolated from 10-d-old sow-reared (SR) or colostrum-deprived formula-fed (FF) pigs were stimulated for 72 h with single HMO, mixtures of single HMO or a complex mixture of HMO isolated from human milk (iHMO). T-cell phenotype, cytokine production and proliferation were measured by flow cytometry, immunoassay and [³H]thymidine incorporation, respectively. Stimulation with HMO had direct effects on PBMC. For instance, cells stimulated with iHMO produced more IL-10 than unstimulated cells, and cells stimulated with fucosylated HMO tended to proliferate less than unstimulated cells. Additionally, co-stimulation with HMO mixtures or single HMO altered PBMC responses to phytohaemagglutinin (PHA) or lipopolysaccharide (LPS) stimulation. Compared with PBMC stimulated with PHA alone, cells co-stimulated with iHMO and PHA proliferated more and had fewer detectable CD4⁺CD8⁺ T cells. Compared with PBMC stimulated by LPS alone, cells co-stimulated with a mixture of sialylated HMO and LPS proliferated more and tended to have fewer detectable CD4⁺ T cells. Differences in the baseline responses of PBMC isolated from the SR or FF pigs were observed. In summary, HMO directly affected PBMC populations and functions. Additionally, ex vivo measurements of PBMC phenotype, cytokine production and proliferation were influenced by the neonate's diet.

A glycosylation-dependent CD45RB epitope defines previously unacknowledged CD27⁻IgM(high) B cell subpopulations enriched in young children and after hematopoietic stem cell transplantation

The immune system is dysfunctional for years after hematopoietic stem cell transplantation (HSCT). A potential cause is an intrinsic B cell deficiency. In a cohort of pediatric HSCT patients few CD27(+) B cells formed after transplantation with the number of CD27(+)IgM(high) cells more affected than class-switched ones. A previously unacknowledged population of CD27(-)IgM(high) cells made up the majority of B cells and this population was also enlarged in healthy children compared to adults. Only a minority of these CD27(-)IgM(high) B cells expressed markers typical for transitional B cells, and the non-transitional CD27(-)IgM(high) cells could be further divided into subpopulations based on their ability to extrude the dye Rhodamine 123 and their expression of CD45RB(MEM55), a glycosylation-dependent epitope. Thus, we define several novel human CD27(-)IgM(high) B cell subpopulations in blood, all of which are present in higher frequencies and numbers in young children and after HSCT than in adults.

Sweeten PAMPs: Role of Sugar Complexed PAMPs in Innate Immunity and Vaccine Biology

Innate sensors play a critical role in the early innate immune responses to invading pathogens through sensing of diverse biochemical signatures also known as pathogen associated molecular patterns (PAMPs). These biochemical signatures primarily consist of a major family of biomolecules such as proteins, lipids, nitrogen bases, and sugar and its complexes, which are distinct from host molecules and exclusively expressed in pathogens and essential to their survival. The family of sensors known as pattern recognition receptors (PRRs) are germ-line encoded, evolutionarily conserved molecules, and consist of Toll-like receptors (TLRs), RIG-I-like receptors (RLRs), NOD-like receptors (NLRs), C-type lectin-like receptors (CLRs), and DNA sensors. Sensing of PAMP by PRR initiates the cascade of signaling leading to the activation of transcription factors, such as NF-κB and interferon regulatory factors (IRFs), resulting in a variety of cellular responses, including the production of interferons (IFNs) and pro-inflammatory cytokines. In this review, we discuss sensing of different types of glycosylated PAMPs such as β-glucan (a polymeric sugar) or lipopolysaccharides, nucleic acid, and so on (sugar complex PAMPs) by different families of sensors, its role in pathogenesis, and its application in development of potential vaccine and vaccine adjuvants.

Glycan synthesis, structure, and dynamics: A selection

Glycan structural information is a prerequisite for elucidation of carbohydrate function in biological systems. To this end we employ a tripod approach for investigation of carbohydrate 3D structure and dynamics based on organic synthesis; different experimental spectroscopy techniques, NMR being of prime importance; and molecular simulations using, in particular, molecular dynamics (MD) simulations. The synthesis of oligosaccharides in the form of glucosyl fluorides is described, and their use as substrates for the Lam16A E115S glucosyl synthase is exemplified as well as a conformational analysis of a cyclic &beta;-(1&rarr;3)-heptaglucan based on molecular simulations. The flexibility of the N-acetyl group of aminosugars is by MD simulations indicated to function as a gatekeeper for transitions of glycosidic torsion angles to other regions of conformational space. A novel approach to visualize glycoprotein (GP) structures is presented in which the protein is shown by, for example, ribbons, but instead of stick or space-filling models for the carbohydrate portion it is visualized by the colored geometrical figures known as CFG representation in a 3D way, which we denote 3D-CFG, thereby effectively highlighting the sugar residues of the glycan part of the GP and the position(s) on the protein.

Cell surface-associated compounds of probiotic lactobacilli sustain the strain-specificity dogma

Probiotic lactobacilli can positively impact on the health status of targeted (diseased) populations but efficacy depends strongly on the strain employed and the molecular basis for this phenomenon is poorly understood. This review discusses the current state-of-the-art in the field of molecular probiotic-host interactions, focusing on subtle strain-specific differences in the biochemical characteristics of cell surface-associated probiotic ligands and the consequences thereof for the immune responses elicited. This research is bound to enhance our understanding of strain-specificity in relation to probiotic functionality and will allow molecular science-based design of screening and characterization assays targeted to improved selection of probiotic candidate strains. Moreover, identified bioactive effector molecules could be isolated or produced for administration in a more pharmacological regime.

Monoclonal antibodies toward different Tn-amino acid backbones display distinct recognition patterns on human cancer cells. Implications for effective immuno-targeting of cancer

The Tn antigen (GalNAcα-O-Ser/Thr) is a well-established tumor-associated marker which represents a good target for the design of anti-tumor vaccines. Several studies have established that the binding of some anti-Tn antibodies could be affected by the density of Tn determinant or/and by the amino acid residues neighboring O-glycosylation sites. In the present study, using synthetic Tn-based vaccines, we have generated a panel of anti-Tn monoclonal antibodies. Analysis of their binding to various synthetic glycopeptides, modifying the amino acid carrier of the GalNAc(*) (Ser* vs Thr*), showed subtle differences in their fine specificities. We found that the recognition of these glycopeptides by some of these MAbs was strongly affected by the Tn backbone, such as a S*S*S* specific MAb (15G9) which failed to recognize a S*T*T* or a T*T*T* structure. Different binding patterns of these antibodies were also observed in FACS and Western blot analysis using three human cancer cell lines (MCF-7, LS174T and Jurkat). Importantly, an immunohistochemical analysis of human tumors (72 breast cancer and 44 colon cancer) showed the existence of different recognition profiles among the five antibodies evaluated, demonstrating that the aglyconic part of the Tn structure (Ser vs Thr) plays a key role in the anti-Tn specificity for breast and colon cancer detection. This new structural feature of the Tn antigen could be of important clinical value, notably due to the increasing interest of this antigen in anticancer vaccine design as well as for the development of anti-Tn antibodies for in vivo diagnostic and therapeutic strategies.

C-type lectin receptor Clec4d plays a protective role in resolution of Gram-negative pneumonia

Pneumonia is frequently associated with sepsis, characterized by a nonresolving hyperinflammation. However, specific host components of the pulmonary milieu that regulate the perpetuation of inflammation and tissue destruction observed in this immune disorder are not clearly understood. We examined the function of Clec4d, an orphan mammalian CLR, in Gram negative pneumonic sepsis caused by KPn. Whereas the WT mice infected with a sublethal dose of bacteria could resolve the infection, the Clec4d(-/-) mice were highly susceptible with a progressive increase in bacterial burden, hyperinflammatory response typical of sepsis, and severe lung pathology. This correlated with a massive accumulation of neutrophils in lungs of infected Clec4d(-/-) mice, which was in contrast with their WT counterparts, where neutrophils transiently infiltrated the lungs. Interestingly, the Clec4d(-/-) neutrophils did not exhibit any defect in bacterial clearance. These results suggest that Clec4d plays an important role in resolution of inflammation, possibly by facilitating neutrophil turnover in lungs. This is the first report depicting the physiological function of Clec4d in a pathological condition. The results can have implications not only in sepsis but also in other inflammatory diseases, where nonresolving inflammation is the root cause of disease development.

Glycopolymer probes of signal transduction

Glycans are key participants in biological processes ranging from reproduction to cellular communication to infection. Revealing glycan roles and the underlying molecular mechanisms by which glycans manifest their function requires access to glycan derivatives that vary systematically. To this end, glycopolymers (polymers bearing pendant carbohydrates) have emerged as valuable glycan analogs. Because glycopolymers can readily be synthesized, their overall shape can be varied, and they can be altered systematically to dissect the structural features that underpin their activities. This review provides examples in which glycopolymers have been used to effect carbohydrate-mediated signal transduction. Our objective is to illustrate how these powerful tools can reveal the molecular mechanisms that underlie carbohydrate-mediated signal transduction.

Lack of galectin-1 or galectin-3 alters B cell deletion and anergy in an autoantibody transgene model

Members of the galectin family of proteins have been shown to regulate the development and the function of immune cells. We previously identified the increased expression of galectin-1 and galectin-3 mRNA and protein in anergic B cells relative to their naïve counterparts. To investigate the role of these galectins in maintaining B cell tolerance, we crossed mice deficient in galectin-1 or galectin-3 with mice bearing a lupus autoantigen-binding transgenic (Tg) B cell receptor, using a model with a well-characterized B cell tolerance phenotype of deletion, receptor editing and anergy. Here, we present data showing that the global knockout of galectin-1 or galectin-3 yields subtle alterations in B cell fate in autoantibody Tg mice. The absence of galectin-3 leads to a significant increase in the number of Tg spleen B cells, with the recovery of anti-laminin antibodies from a subset of mice. The B cell number increases further in antibody Tg mice with the dual deficiency of both galectin-1 and galectin-3. Isolated galectin-1 deficiency significantly enhances the proliferation of Tg B cells in response to lipopolysaccharide stimulation. These findings add to the growing body of evidence indicating a role for the various galectin family members, and for galectins 1 and 3 in particular, in the regulation of autoimmunity.

Development of orally active inhibitors of protein and cellular fucosylation

The key role played by fucose in glycoprotein and cellular function has prompted significant research toward identifying recombinant and biochemical strategies for blocking its incorporation into proteins and membrane structures. Technologies surrounding engineered cell lines have evolved for the inhibition of in vitro fucosylation, but they are not applicable for in vivo use and drug development. To address this, we screened a panel of fucose analogues and identified 2-fluorofucose and 5-alkynylfucose derivatives that depleted cells of GDP-fucose, the substrate used by fucosyltransferases to incorporate fucose into protein and cellular glycans. The inhibitors were used in vitro to generate fucose-deficient antibodies with enhanced antibody-dependent cellular cytotoxicity activities. When given orally to mice, 2-fluorofucose inhibited fucosylation of endogenously produced antibodies, tumor xenograft membranes, and neutrophil adhesion glycans. We show that oral 2-fluorofucose treatment afforded complete protection from tumor engraftment in a syngeneic tumor vaccine model, inhibited neutrophil extravasation, and delayed the outgrowth of tumor xenografts in immune-deficient mice. The results point to several potential therapeutic applications for molecules that selectively block the endogenous generation of fucosylated glycan structures.

The development of synthetic antitumour vaccines from mucin glycopeptide antigens

Based on important cell-biological and biochemical results concerning the structural difference between membrane glycoproteins of normal epithelial cells and epithelial tumour cells, tumour-associated glycopeptide antigens have been chemically synthesised and structurally confirmed. Glycopeptide structures of the tandem repeat sequence of mucin MUC1 of epithelial tumour cells constitute the most promising tumour-associated antigens. In order to generate a sufficient immunogenicity of these endogenous structures, usually tolerated by the immune system, these synthetic glycopeptide antigens were conjugated to immune stimulating components: in fully synthetic two-component vaccines either with T-cell peptide epitopes or with Toll-like receptor2 lipopeptide ligands or in three-component vaccines with both these stimulants. Alternatively, the synthetic glycopeptide antigens were coupled to immune stimulating carrier proteins. In particular, MUC1 glycopeptide conjugates with Tetanus toxoid proved to be efficient vaccines inducing very strong immune responses in mice. The antibodies elicited with the fully synthetic vaccines showed selective recognition of the tumour-associated glycopeptides as was shown by neutralisation and micro-array binding experiments. After booster immunisations, most of the immune responses showed the installation of an immunological memory. Immunisation with fully synthetic three-component vaccines induced immune reactions with therapeutic effects in terms of reduction of the tumour burden in mice or in killing of tumour cells in culture, while MUC1 glycopeptide-Tetanus toxoid vaccines elicited antibodies in mice which recognised tumour cells in human tumour tissues. The results achieved so far are considered to be promising for the development of an active immunisation against tumours.

Global comparisons of lectin-glycan interactions using a database of analyzed glycan array data

Lectin-glycan interactions have critical functions in multiple normal and pathological processes, but the binding partners and functions for many glycans and lectins are not known. An important step in better understanding glycan-lectin biology is enabling systematic quantification and analysis of the interactions. Glycan arrays can provide the experimental information for such analyses, and the thousands of glycan array datasets available through the Consortium for Functional Glycomics provide the opportunity to extend the analyses to a broad scale. We developed software, based on our previously described Motif Segregation algorithm, for the automated analysis of glycan array data, and we analyzed the entire storehouse of 2883 datasets from the Consortium for Functional Glycomics. We mined the resulting database to make comparisons of specificities across multiple lectins and comparisons between glycans in their lectin receptors. Of the lectins in the database, viral lectins were the most different from other organism types, with specificities nearly always restricted to sialic acids, and mammalian lectins had the most diverse range of specificities. Certain mammalian lectins were unique in their specificities for sulfated glycans. Simple modifications to a lactosamine core structure radically altered the types of lectins that were highly specific for the glycan. Unmodified lactosamine was specifically recognized by plant, fungal, viral, and mammalian lectins; sialylation shifted the binding mainly to viral lectins; and sulfation resulted in mainly mammalian lectins with the highest specificities. We anticipate that this analysis program and database will be valuable in fundamental glycobiology studies, detailed analyses of lectin specificities, and practical applications in translational research.

Sialic acid: a sweet swing between mammalian host and Trypanosoma cruzi

Commonly found at the outermost ends of complex carbohydrates in extracellular medium or on outer cell membranes, sialic acids play important roles in a myriad of biological processes. Mammals synthesize sialic acid through a complex pathway, but Trypanosoma cruzi, the agent of Chagas’ disease, evolved to obtain sialic acid from its host through a trans-sialidase (TcTS) reaction. Studies of the parasite cell surface architecture and biochemistry indicate that a unique system comprising sialoglycoproteins and sialyl-binding proteins assists the parasite in several functions including parasite survival, infectivity, and host–cell recognition. Additionally, TcTS activity is capable of extensively remodeling host cell glycomolecules, playing a role as virulence factor. This review presents the state of the art of parasite sialobiology, highlighting how the interplay between host and parasite sialic acid helps the pathogen to evade host defense mechanisms and ensure lifetime host parasitism.

Progress Toward a Human Vaccine Against Coccidioidomycosis

Coccidioidomycosis (San Joaquin Valley fever) is a human respiratory disease caused by a soil-borne mold, and is recognized as an intransigent microbial infection by physicians who treat patients with the potentially life-threatening, disseminated form of this mycosis. Epidemiological studies based on surveys of skin-test reactivity of people who reside in the endemic regions of the Southwestern US have shown that at least 150,000 new infections occur annually. The clinical spectrum of coccidioidomycosis ranges from an asymptomatic insult to a severe pulmonary disease in which the pathogen may spread from the lungs to the skin, bones, brain and other body organs. Escalation of symptomatic infections and increased cost of long-term antifungal treatment warrant a concerted effort to develop a vaccine against coccidioidomycosis. This review examines recently reported strategies used to generate such a vaccine and summarizes current understanding of the nature of protective immunity to this formidable disease.

Galectin-1 confers immune privilege to human trophoblast: implications in recurrent fetal loss

Mechanisms accounting for the protection of the fetal semi-allograft from maternal immune cells remain incompletely understood. In previous studies, we showed that galectin-1 (Gal1), an immunoregulatory glycan-binding protein, hierarchically triggers a cascade of tolerogenic events at the mouse fetomaternal interface. Here, we show that Gal1 confers immune privilege to human trophoblast cells through the modulation of a number of regulatory mechanisms. Gal1 was mainly expressed in invasive extravillous trophoblast cells of human first trimester and term placenta in direct contact with maternal tissue. Expression of Gal1 by the human trophoblast cell line JEG-3 was primarily controlled by progesterone and pro-inflammatory cytokines and impaired T-cell responses by limiting T cell viability, suppressing the secretion of Th1-type cytokines and favoring the expansion of CD4(+)CD25(+)FoxP3(+) regulatory T (T(reg)) cells. Targeted inhibition of Gal1 expression through antibody (Ab)-mediated blockade, addition of the specific disaccharide lactose or retroviral-mediated siRNA strategies prevented these immunoregulatory effects. Consistent with a homeostatic role of endogenous Gal1, patients with recurrent pregnancy loss showed considerably lower levels of circulating Gal1 and had higher frequency of anti-Gal1 auto-Abs in their sera compared with fertile women. Thus, endogenous Gal1 confers immune privilege to human trophoblast cells by triggering a broad tolerogenic program with potential implications in threatened pregnancies.