Mammalian N-glycan branching protects against innate immune self-recognition and inflammation in autoimmune disease pathogenesis

Impact of the Niemann-Pick c1 Gene Mutation on the Total Cellular Glycomics of CHO Cells

Niemann-Pick disease type C (NPC) is an autosomal recessive lipid storage disorder, and the majority of cases are caused by mutations in the NPC1 gene. In this study, we clarified how a single gene mutation in the NPC1 gene impacts the cellular glycome by analyzing the total glycomic expression profile of Chinese hamster ovary cell mutants defective in the Npc1 gene (Npc1 KO CHO cells). A number of glycomic alterations were identified, including increased expression of lactosylceramide, GM1, GM2, GD1, various neolacto-series glycosphingolipids, and sialyl-T (O-glycan), which was found to be the major sialylated protein-bound glycan, as well as various N-glycans, which were commonly both fucosylated and sialylated. We also observed significant increases in the total amounts of free oligosaccharides (fOSs), especially in the unique complex- and hybrid-type fOSs. Treatment of Npc1 KO CHO cells with 2-hydroxypropyl-β-cyclodextrin (HPBCD), which can reduce cholesterol and glycosphingolipid (GSL) storage, did not affect the glycomic alterations observed in the GSL-, N-, and O-glycans of Npc1 KO CHO cells. However, HPBCD treatment corrected the glycomic alterations observed in fOSs to levels observed in wild-type cells.

Enhancement of macrophage inflammatory responses by CCL2 is correlated with increased miR-9 expression and downregulation of the ERK1/2 phosphatase Dusp6

Macrophage polarization plays a central role in both protective immunity and immunopathology. While the role of cytokines in driving macrophage polarization is well characterized, less is understood about the role of chemokines. The purpose of this study was to determine if CC chemokine 2 (CCL2/MCP1) could influence macrophage polarization in response to subsequent activation with cytokines and microbial products. Treatment of bone marrow-derived macrophages with CCL2 alone did not result in increased expression of either classical or alternatively-activated macrophage genes as compared to standard skewing cytokines or Toll-like receptor agonists. However, subsequent stimulation of CCL2 pre-treated macrophages with classical activation stimuli resulted in enhanced expression of genes associated with classical activation. This enhancement correlated with increased phosphorylation of ERK1/2 kinases, a decrease in expression of the ERK phosphatase Dusp6 and enhanced expression of miR-9. These results indicate that CCL2 supports the classical activation of macrophages, with miR-9 mediated down-regulation of Dusp6 and enhanced ERK-mediated signal transduction possibly mediating this enhanced pro-inflammatory gene expression.

C-Type Lectin Receptor Dectin-2 Binds to an Endogenous Protein β-Glucuronidase on Dendritic Cells

C-type lectin receptors (CLRs) recognize pathogen-derived ligands and abnormal self that trigger protective immune responses. However, the precise nature of self ligands recognized by CLRs remains to be determined. Here, we found that Dectin-2 recognizes bone marrow-derived dendritic cells (BMDCs) using Dectin-2-expressing reporter cells. This activity was inhibited by an excessive amount of mannose, and by the mutation of mannose-binding motif in Dectin-2. β-glucuronidase (Gusb) was identified as a protein bound to Dectin-2 and mutations of N-glycosylation sites in Gusb impaired the binding of Gusb to Dectin-2. Overexpression of Gusb in a macrophage cell line conferred an ability to stimulate Dectin-2-expressing reporter cells. Our study suggests that a glycosylated protein with mannose-related structure is recognized by Dectin-2.

Isomeranzin suppresses inflammation by inhibiting M1 macrophage polarization through the NF-κB and ERK pathway

Macrophage polarization plays an important role in inflammation. Regulation of the polarization has been reported to be effective therapeutics for various kinds of inflammatory diseases. The aims of the present study were to investigate the anti-inflammatory property of isomeranzin isolating from Murraya exotica as well as potential molecular mechanisms. Results showed that isomeranzin specifically reduced the M1 macrophage-associated pro-inflammatory cytokines through down-regulation of NF-κB and ERK signals. Immunoprecipitation and RNA silencing indicated suppression of isomeranzin in NF-κB activation was relying on the decreasing of TRAF6 ubiquitination. In vivo studies showed isomeranzin evidently inhibited LPS-induced sepsis for rising survival rate, improving tissue damage and lessening inflammatory cytokines. In accordance with in vitro studies, isomeranzin significantly blocked expression of p-p65 and p-ERK in lung and liver tissues. Moreover, isomeranzin ameliorated DSS and TNBS-induced colitis due to its anti-inflammatory effects. Taken together, isomeranzin suppressed inflammatory diseases by controlling M1 macrophage polarization through the NF-κB and ERK pathway.

Emerging roles of protein mannosylation in inflammation and infection

Proteins are frequently modified by complex carbohydrates (glycans) that play central roles in maintaining the structural and functional integrity of cells and tissues in humans and lower organisms. Mannose forms an essential building block of protein glycosylation, and its functional involvement as components of larger and diverse α-mannosidic glycoepitopes in important intra- and intercellular glycoimmunological processes is gaining recognition. With a focus on the mannose-rich asparagine (N-linked) glycosylation type, this review summarises the increasing volume of literature covering human and non-human protein mannosylation, including their structures, biosynthesis and spatiotemporal expression. The review also covers their known interactions with specialised host and microbial mannose-recognising C-type lectin receptors (mrCLRs) and antibodies (mrAbs) during inflammation and pathogen infection. Advances in molecular mapping technologies have recently revealed novel immuno-centric mannose-terminating truncated N-glycans, termed paucimannosylation, on human proteins. The cellular presentation of α-mannosidic glycoepitopes on N-glycoproteins appears tightly regulated; α-mannose determinants are relative rare glycoepitopes in physiological extracellular environments, but may be actively secreted or leaked from cells to transmit potent signals when required. Simultaneously, our understanding of the molecular basis on the recognition of mannosidic epitopes by mrCLRs including DC-SIGN, mannose receptor, mannose binding lectin and mrAb is rapidly advancing, together with the functional implications of these interactions in facilitating an effective immune response during physiological and pathophysiological conditions. Ultimately, deciphering these complex mannose-based receptor-ligand interactions at the detailed molecular level will significantly advance our understanding of immunological disorders and infectious diseases, promoting the development of future therapeutics to improve patient clinical outcomes.

Association of systemic lupus erythematosus with decreased immunosuppressive potential of the IgG glycome

Objective

Glycans attached to the Fc portion of IgG are important modulators of IgG effector functions. Interindividual differences in IgG glycome composition are large and they associate strongly with different inflammatory and autoimmune diseases. IKZF1, HLA–DQ2A/B, and BACH2 genetic loci that affect IgG glycome composition show pleiotropy with systemic lupus erythematosus (SLE), indicating a potentially causative role of aberrant IgG glycosylation in SLE. We undertook this large multicenter case–control study to determine whether SLE is associated with altered IgG glycosylation.

Methods

Using ultra‐performance liquid chromatography analysis of released glycans, we analyzed the composition of the IgG glycome in 261 SLE patients and 247 matched controls of Latin American Mestizo origin (the discovery cohort) and in 2 independent replication cohorts of different ethnicity (108 SLE patients and 193 controls from Trinidad, and 106 SLE patients and 105 controls from China).

Results

Multiple statistically significant differences in IgG glycome composition were observed between patients and controls. The most significant changes included decreased galactosylation and sialylation of IgG (which regulate proinflammatory and antiinflammatory actions of IgG) as well as decreased core fucose and increased bisecting N‐acetylglucosamine (which affect antibody‐dependent cell‐mediated cytotoxicity).

Conclusion

The IgG glycome in SLE patients is significantly altered in a way that decreases immunosuppressive action of circulating immunoglobulins. The magnitude of observed changes is associated with the intensity of the disease, indicating that aberrant IgG glycome composition or changes in IgG glycosylation may be an important molecular mechanism in SLE.

Genome-Wide Pathway Analysis Identifies Genetic Pathways Associated with Psoriasis

Psoriasis is a chronic inflammatory disease with a complex genetic architecture. To date, the psoriasis heritability is only partially explained. However, there is increasing evidence that the missing heritability in psoriasis could be explained by multiple genetic variants of low effect size from common genetic pathways. The objective of this study was to identify new genetic variation associated with psoriasis risk at the pathway level. We genotyped 598,258 single nucleotide polymorphisms in a discovery cohort of 2,281 case-control individuals from Spain. We performed a genome-wide pathway analysis using 1,053 reference biological pathways. A total of 14 genetic pathways (PFDR ≤ 2.55 × 10(-2)) were found to be significantly associated with psoriasis risk. Using an independent validation cohort of 7,353 individuals from the UK, a total of 6 genetic pathways were significantly replicated (PFDR ≤ 3.46 × 10(-2)). We found genetic pathways that had not been previously associated with psoriasis risk such as retinol metabolism (Pcombined = 1.84 × 10(-4)), the transport of inorganic ions and amino acids (Pcombined = 1.57 × 10(-7)), and post-translational protein modification (Pcombined = 1.57 × 10(-7)). In the latter pathway, MGAT5 showed a strong network centrality, and its association with psoriasis risk was further validated in an additional case-control cohort of 3,429 individuals (P < 0.05). These findings provide insights into the biological mechanisms associated with psoriasis susceptibility.

Cytosolic Nuclease TREX1 Regulates Oligosaccharyltransferase Activity Independent of Nuclease Activity to Suppress Immune Activation

TREX1 is an endoplasmic reticulum (ER)-associated negative regulator of innate immunity. TREX1 mutations are associated with autoimmune and autoinflammatory diseases. Biallelic mutations abrogating DNase activity cause autoimmunity by allowing immunogenic self-DNA to accumulate, but it is unknown how dominant frameshift (fs) mutations that encode DNase-active but mislocalized proteins cause disease. We found that the TREX1 C terminus suppressed immune activation by interacting with the ER oligosaccharyltransferase (OST) complex and stabilizing its catalytic integrity. C-terminal truncation of TREX1 by fs mutations dysregulated the OST complex, leading to free glycan release from dolichol carriers, as well as immune activation and autoantibody production. A connection between OST dysregulation and immune disorders was demonstrated in Trex1(-/-) mice, TREX1-V235fs patient lymphoblasts, and TREX1-V235fs knock-in mice. Inhibiting OST with aclacinomycin corrects the glycan and immune defects associated with Trex1 deficiency or fs mutation. This function of the TREX1 C terminus suggests a potential therapeutic option for TREX1-fs mutant-associated diseases.

HMGB1 Promotes Systemic Lupus Erythematosus by Enhancing Macrophage Inflammatory Response

Background/Purpose. HMGB1, which may act as a proinflammatory mediator, has been proposed to contribute to the pathogenesis of multiple chronic inflammatory and autoimmune diseases including systemic lupus erythematosus (SLE); however, the precise mechanism of HMGB1 in the pathogenic process of SLE remains obscure. Method. The expression of HMGB1 was measured by ELISA and western blot. The ELISA was also applied to detect proinflammatory cytokines levels. Furthermore, nephritic pathology was evaluated by H&E staining of renal tissues. Results. In this study, we found that HMGB1 levels were significantly increased and correlated with SLE disease activity in both clinical patients and murine model. Furthermore, gain- and loss-of-function analysis showed that HMGB1 exacerbated the severity of SLE. Of note, the HMGB1 levels were found to be associated with the levels of proinflammatory cytokines such as TNF-α and IL-6 in SLE patients. Further study demonstrated that increased HMGB1 expression deteriorated the severity of SLE via enhancing macrophage inflammatory response. Moreover, we found that receptor of advanced glycation end products played a critical role in HMGB1-mediated macrophage inflammatory response. Conclusion. These findings suggested that HMGB1 might be a risk factor for SLE, and manipulation of HMGB1 signaling might provide a therapeutic strategy for SLE.

Mechanisms Underlying the Immunogenicity of Therapeutic Proteins: Risk Assessment and Management Strategies

Antibodies to therapeutic proteins have caused serious adverse events and loss of efficacy in patients. Therefore, it is critical to manage the risk of antitherapeutic antibodies (ATA) during drug development and in the postmarketing environment. Risk assessments are an important tool for managing immunogenicity risk because they provide a format for considering the consequences and likelihood of ATA development. Because many factors influence both the severity of the consequences and likelihood of ATA development, successful risk assessments require input from all relevant disciplines, including product quality, manufacturing, nonclinical, pharmacology, and clinical. The results of risk assessments are used to develop appropriate risk reduction strategies, which may include product quality and manufacturing controls and elements of clinical trial design. This article discusses considerations for immunogenicity risk assessments and management.

TSC1 controls macrophage polarization to prevent inflammatory disease

Macrophages acquire distinct phenotypes during tissue stress and inflammatory responses, but the mechanisms that regulate the macrophage polarization are poorly defined. Here we show that tuberous sclerosis complex 1 (TSC1) is a critical regulator of M1 and M2 phenotypes of macrophages. Mice with myeloid-specific deletion of TSC1 exhibit enhanced M1 response and spontaneously develop M1-related inflammatory disorders. However, TSC1-deficient mice are highly resistant to M2-polarized allergic asthma. Inhibition of the mammalian target of rapamycin (mTOR) fails to reverse the hypersensitive M1 response of TSC1-deficient macrophages, but efficiently rescues the defective M2 polarization. Deletion of mTOR also fails to reverse the enhanced inflammatory response of TSC1-deficient macrophages. Molecular studies indicate that TSC1 inhibits M1 polarization by suppressing the Ras GTPase-Raf1-MEK-ERK pathway in mTOR-independent manner, whereas TSC1 promotes M2 properties by mTOR-dependent CCAAT/enhancer-binding protein-β pathways. Overall, these findings define a key role for TSC1 in orchestrating macrophage polarization via mTOR-dependent and independent pathways.

CNS myelin induces regulatory functions of DC-SIGN-expressing, antigen-presenting cells via cognate interaction with MOG

Human myelin oligodendrocyte glycoprotein is decorated with fucosylated N-glycans that are recognized by DC-SIGN⁺ DCs and microglia that control immune homeostasis.

Myelin oligodendrocyte glycoprotein (MOG), a constituent of central nervous system myelin, is an important autoantigen in the neuroinflammatory disease multiple sclerosis (MS). However, its function remains unknown. Here, we show that, in healthy human myelin, MOG is decorated with fucosylated N-glycans that support recognition by the C-type lectin receptor (CLR) DC-specific intercellular adhesion molecule-3–grabbing nonintegrin (DC-SIGN) on microglia and DCs. The interaction of MOG with DC-SIGN in the context of simultaneous TLR4 activation resulted in enhanced IL-10 secretion and decreased T cell proliferation in a DC-SIGN-, glycosylation-, and Raf1-dependent manner. Exposure of oligodendrocytes to proinflammatory factors resulted in the down-regulation of fucosyltransferase expression, reflected by altered glycosylation at the MS lesion site. Indeed, removal of fucose on myelin reduced DC-SIGN–dependent homeostatic control, and resulted in inflammasome activation, increased T cell proliferation, and differentiation toward a Th₁₇-prone phenotype. These data demonstrate a new role for myelin glycosylation in the control of immune homeostasis in the healthy human brain through the MOG–DC-SIGN homeostatic regulatory axis, which is comprised by inflammatory insults that affect glycosylation. This phenomenon should be considered as a basis to restore immune tolerance in MS.

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.

Identification of distinct ligands for the C-type lectin receptors Mincle and Dectin-2 in the pathogenic fungus Malassezia

Various C-type lectin receptors (CLRs), including Mincle and Dectin-2, function as pattern recognition receptors and play a central role in immunity to fungal pathogens. However, the precise structures of the CLR ligands in various pathogenic fungi have yet to be completely defined. Here we report that Malassezia, an opportunistic skin fungal pathogen, is cooperatively recognized by Mincle and Dectin-2 through distinct ligands. Solvent-based fractionation revealed that Mincle and Dectin-2 recognize lipophilic and hydrophilic components of Malassezia, respectively. Mass spectrometry and nuclear magnetic resonance (NMR) revealed glyceroglycolipid and unique mannosyl fatty acids linked to mannitol as two Mincle ligands. An O-linked mannobiose-rich glycoprotein was identified as a Malassezia ligand for Dectin-2. Cytokine production in response to the Mincle ligands and the Dectin-2 ligand was abrogated in Mincle(-/-) and Dectin-2(-/-) dendritic cells, respectively. These results demonstrate that Mincle and Dectin-2 recognize distinct ligands in Malassezia to induce host immune responses.

Emerging principles for the therapeutic exploitation of glycosylation

Glycosylation plays a key role in a wide range of biological processes. Specific modification to a glycan's structure can directly modulate its biological function. Glycans are not only essential to glycoprotein folding, cellular homeostasis, and immune regulation but are involved in multiple disease conditions. An increased molecular and structural understanding of the mechanistic role that glycans play in these pathological processes has driven the development of therapeutics and illuminated novel targets for drug design. This knowledge has enabled the treatment of metabolic disorders and the development of antivirals and shaped cancer and viral vaccine strategies. Furthermore, an understanding of glycosylation has led to the development of specific drug glycoforms, for example, monoclonal antibodies, with enhanced potency.

Human T cell activation results in extracellular signal-regulated kinase (ERK)-calcineurin-dependent exposure of Tn antigen on the cell surface and binding of the macrophage galactose-type lectin (MGL)

The C-type lectin macrophage galactose-type lectin (MGL) exerts an immunosuppressive role reflected by its interaction with terminal GalNAc moieties, such as the Tn antigen, on CD45 of effector T cells, thereby down-regulating T cell receptor signaling, cytokine responses, and induction of T cell death. Here, we provide evidence for the pathways that control the specific expression of GalNAc moieties on human CD4(+) T cells. GalNAc epitopes were readily detectable on the cell surface after T cell activation and required de novo protein synthesis. Expression of GalNAc-containing MGL ligands was completely dependent on PKC and did not involve NF-κB. Instead, activation of the downstream ERK MAPK pathway led to decreased mRNA levels and activity of the core 1 β3GalT enzyme and its chaperone Cosmc, favoring the expression of Tn antigen. In conclusion, expression of GalNAc moieties mirrors the T cell activation status, and thus only highly stimulated T cells are prone to the suppressive action of MGL.

Heterogenic endothelial responses to inflammation: role for differential N-glycosylation and vascular bed of origin

BACKGROUND

Endothelial cell responses during inflammation are heterogeneous and key for selectivity in how leukocytes hone in on specific sites and why vascular diseases are highly bed specific. However, mechanisms for this specificity remain unclear.

METHODS AND RESULTS

Here, we exposed human endothelial cells isolated from 5 systemic arterial beds from 1 donor (to overcome donor-to-donor genetic/epigenetic differences), the umbilical vein, and pulmonary microvasculature to TNF-α, LPS, and IL-1β and assessed acute (ERK1/2 and p65) and chronic (ICAM-1, VCAM-1 total and surface expression) signaling responses and assessed changes in surface N-glycans and monocyte adhesion. Significant diversity in responses was evident by disparate changes in ERK1/2 and p65 NF-κB phosphorylation, which varied up to 5-fold between different cells and in temporal and magnitude differences in ICAM-1 and VCAM-1 expression (maximal VCAM-1 induction typically being observed by 4 hours, whereas ICAM-1 expression was increased further at 24 hours relative to 4 hours). N-glycan profiles both basally and with stimulation were also bed specific, with hypoglycosylated N-glycans correlating with increased THP-1 monocyte adhesion. Differences in surface N-glycan expression tracked with dynamic up- or downregulation of α-mannosidase activity during inflammation.

CONCLUSIONS

These results demonstrate a critical role for the vascular bed of origin in controlling endothelial responses and function to inflammatory stimuli and suggest that bed-specific expression of N-linked sugars may provide a signature for select leukocyte recruitment.

Identification of a high-mannose ICAM-1 glycoform: effects of ICAM-1 hypoglycosylation on monocyte adhesion and outside in signaling

Endothelial adhesion molecules are critical effectors of inflammation ensuring coordinated interactions that allow leukocytes to home to sites of injury. These adhesion molecules are often extensively modified posttranslationaly by the addition of N-glycans, but if, or how, these modifications contribute to the protein function remains poorly understood. Herein we show that activated endothelial cells express two distinct N-glycoforms of intercellular adhesion molecule 1 (ICAM-1) that comprise a complex N-glycoform with α-2,6 sialic acid present at relatively high levels and a second, less abundant and previously undescribed high-mannose glycoform (HM-ICAM-1). This novel HM-ICAM-1 glycoform was also detected in human coronary artery specimens and moreover appeared to be the dominant glycoform in vivo. Production of exclusively HM-ICAM-1 in cells by α-mannosidase inhibition increased monocyte rolling and adhesion compared with mature ICAM-1 consistent with high-mannose epitopes providing leukocyte ligands. Cross-linking of ICAM-1 transmits outside-in signals that affect endothelial permeability and survival. Interestingly, cell signaling (assessed using ERK, VE-cadherin, and Akt phosphorylation) was maintained after cross-linking of HM-ICAM-1 compared with mature ICAM-1; however, interactions with the actin cytoskeleton were lost with HM-ICAM-1. These findings suggest that specific ICAM-1 N-glycoforms modulate distinct aspects of the inflammatory response and identify HM-ICAM-1 as a new therapeutic target for controlling leukocyte trafficking and endothelial inflammation.

Inducible colitis-associated glycome capable of stimulating the proliferation of memory CD4+ T cells

The colitis-associated glycome mediates CD4⁺ T cell expansion and contributes to the exacerbation of T cell–mediated intestinal inflammation.

Immune responses are modified by a diverse and abundant repertoire of carbohydrate structures on the cell surface, which is known as the glycome. In this study, we propose that a unique glycome that can be identified through the binding of galectin-4 is created on local, but not systemic, memory CD4⁺ T cells under diverse intestinal inflammatory conditions, but not in the healthy state. The colitis-associated glycome (CAG) represents an immature core 1–expressing O-glycan. Development of CAG may be mediated by down-regulation of the expression of core-2 β1,6-N-acetylglucosaminyltransferase (C2GnT) 1, a key enzyme responsible for the production of core-2 O-glycan branch through addition of N-acetylglucosamine (GlcNAc) to a core-1 O-glycan structure. Mechanistically, the CAG seems to contribute to super raft formation associated with the immunological synapse on colonic memory CD4⁺ T cells and to the consequent stabilization of protein kinase C θ activation, resulting in the stimulation of memory CD4⁺ T cell expansion in the inflamed intestine. Functionally, CAG-mediated CD4⁺ T cell expansion contributes to the exacerbation of T cell–mediated experimental intestinal inflammations. Therefore, the CAG may be an attractive therapeutic target to specifically suppress the expansion of effector memory CD4⁺ T cells in intestinal inflammation such as that seen in inflammatory bowel disease.

Chemo-enzymatic synthesis and in vitro cytokine profiling of tailor-made oligofructosides

Background

It is well known that carbohydrates play fundamental roles in cell signaling and infection processes as well as tumor formation and progression. However, the interaction pathways and cellular receptors targeted by carbohydrates and glycoconjugates remain poorly examined and understood. This lack of research stems, at least to a major part, from accessibility problems of large, branched oligosaccharides.

Results

To test glycan - cell interactions in vitro, a variety of tailored oligosaccharides was synthesized chemo-enzymatically. Glycosyltransferases from the GRAS organisms Bacillus megaterium (SacB) and Aspergillus niger (Suc1) were used in this study. Substrate engineering of these glycosyltransferases generally acting on sucrose leads to the controlled formation of novel tailored di-, tri- and tetrasaccharides. Already industrially used as prebiotics in functional food, the immunogenic potential of novel oligosaccharides was characterized in this study. A differential secretion of CXCL8 and CCL2 was observed upon oligosaccharide co-cultivation with colorectal epithelial Caco-2 cells.

Conclusion

Pure carbohydrates are able to stimulate a cytokine response in human endothelial cells in vitro. The type and amount of cytokine secretion depends on the type of co-cultivated oligosaccharide.

Why must T cells be cross-reactive?

Clonal selection theory proposed that individual T cells are specific for a single peptide-MHC antigen. However, the repertoire of αβ T cell receptors (TCRs) is dwarfed by the vast array of potential foreign peptide-MHC complexes, and a comprehensive system requires each T cell to recognize numerous peptides and thus be cross-reactive. This compromise on specificity has profound implications because the chance of any natural peptide-MHC ligand being an optimal fit for its cognate TCR is small, as there will almost always be more-potent agonists. Furthermore, any TCR raised against a specific peptide-MHC complex in vivo can only be the best available solution from the naive T cell pool and is unlikely to be the best possible solution from the substantially greater number of TCRs that could theoretically be produced. This 'systems view' of TCR recognition provides a plausible cause for autoimmune disease and substantial scope for multiple therapeutic interventions.

Role of endothelial N-glycan mannose residues in monocyte recruitment during atherogenesis

OBJECTIVE

Upregulated expression of endothelial adhesion molecules and subsequent binding to cognate monocytic receptors are established paradigms in atherosclerosis. However, these proteins are the scaffolds, with their posttranslational modification with sugars providing the actual ligands. We recently showed that tumor necrosis factor-α increased hypoglycosylated (mannose-rich) N-glycans on the endothelial surface. In the present study, our aim was to determine whether (1) hypoglycosylated N-glycans are upregulated by proatherogenic stimuli (oscillatory flow) in vitro and in vivo, and (2) mannose residues on hypoglycosylated endothelial N-glycans mediate monocyte rolling and adhesion.

METHODS AND RESULTS

Staining with the mannose-specific lectins concanavalin A and lens culinaris agglutinin was increased in human aortic endothelial cells exposed to oscillatory shear or tumor necrosis factor-α and at sites of plaque development and progression in both mice and human vessels. Increasing surface N-linked mannose by inhibiting N-glycan processing potentiated monocyte adhesion under flow during tumor necrosis factor-α stimulation. Conversely, enzymatic removal of high-mannose N-glycans, or masking mannose residues with lectins, significantly decreased monocyte adhesion under flow. These effects occurred without altering induced expression of adhesion molecule proteins.

CONCLUSIONS

Hypoglycosylated (high mannose) N-glycans are present on the endothelial cell surface at sites of early human lesion development and are novel effectors of monocyte adhesion during atherogenesis.

Regulatory circuits mediated by lectin-glycan interactions in autoimmunity and cancer

Numerous regulatory programs have been identified that contribute to the restoration of homeostasis at the conclusion of immune responses and to safeguarding against the detrimental effects of chronic inflammation and autoimmune pathology. Malignant cells may usurp these pathways to create immunosuppressive networks that thwart antitumor responses. Herein we review the role of endogenous lectins (C-type lectins, siglecs, and galectins) and specific N- and O-glycans generated by the coordinated action of glycosyltransferases and glycosidases that together promote regulatory signals that control immune cell homeostasis. We also discuss the mechanisms by which glycan-dependent regulatory programs integrate into canonical circuits that amplify or silence immune responses related to autoimmunity and neoplastic disease.

Pathogenesis of multiple sclerosis via environmental and genetic dysregulation of N-glycosylation

Autoimmune diseases such as multiple sclerosis (MS) result from complex and poorly understood interactions of genetic and environmental factors. A central role for T cells in MS is supported by mouse models, association of the major histocompatibility complex region, and association of critical T cell growth regulator genes such as interleukin-2 receptor (IL-2RA) and interleukin-7 receptor (IL-7RA). Multiple environmental factors (vitamin D(3) deficiency and metabolism) converge with multiple genetic variants (IL-7RA, IL-2RA, MGAT1, and CTLA-4) to dysregulate Golgi N-glycosylation in MS, resulting in T cell hyperactivity, loss of self-tolerance and in mice, a spontaneous MS-like disease with neurodegeneration. Here, we review the genetic and biological interactions that regulate MS pathogenesis through dysregulation of N-glycosylation and how this may enable individualized therapeutic approaches.

Infection, inflammation and host carbohydrates: a Glyco-Evasion Hypothesis

Microbial immune evasion can be achieved through the expression, or mimicry, of host-like carbohydrates on the microbial cell surface to hide from detection. However, disparate reports collectively suggest that evasion could also be accomplished through the modulation of the host glycosylation pathways, a mechanism that we call the "Glyco-Evasion Hypothesis". Here, we will summarize the evidence in support of this paradigm by reviewing three separate bodies of work present in the literature. We review how infection and inflammation can lead to host glycosylation changes, how host glycosylation changes can increase susceptibility to infection and inflammation and how glycosylation impacts molecular and cellular function. Then, using these data as a foundation, we propose a unifying hypothesis in which microbial products can hijack host glycosylation to manipulate the immune response to the advantage of the pathogen. This model reveals areas of research that we believe could significantly improve our fight against infectious disease.

Glycobiology of immune responses

Unlike their protein "roommates" and their nucleic acid "cousins," carbohydrates remain an enigmatic arm of biology. The central reason for the difficulty in fully understanding how carbohydrate structure and biological function are tied is the nontemplate nature of their synthesis and the resulting heterogeneity. The goal of this collection of expert reviews is to highlight what is known about how carbohydrates and their binding partners-the microbial (non-self), tumor (altered-self), and host (self)-cooperate within the immune system, while also identifying areas of opportunity to those willing to take up the challenge of understanding more about how carbohydrates influence immune responses. In the end, these reviews will serve as specific examples of how carbohydrates are as integral to biology as are proteins, nucleic acids, and lipids. Here, we attempt to summarize general concepts on glycans and glycan-binding proteins (mainly C-type lectins, siglecs, and galectins) and their contributions to the biology of immune responses in physiologic and pathologic settings.

Cross-reactive antibodies to target proteins are dependent upon oligomannose glycosylated epitopes in HTLV-1 associated neurological disease

Our lab recently identified a cross-reactive antibody response between human T-lymphotropic virus type-1-p24-(gag) (HTLV-1-p24-(gag)) and peroxiredoxin-1 (PrX-1) as potentially contributing to the pathogenesis of HTLV-1 associated neurological disease via molecular mimicry. These targets proteins were glycosylated, yet the glycan side chains immunoreactive with the immunoglobulins were unknown. Using a combination of lectin isolation and serial enzymatic deglycosylation of glycoproteins, we determined that the immunoreactive epitopes contained branched oligomannose side chains. These data suggest that post-translational glycosylation specifically related to oligomannose immunoreactivity to both the infecting and host antigens may contribute to molecular mimicry and be important in the pathogenesis of HTLV-1 associated neurological disease.

Identification of quantitative trait loci in experimental epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is a chronic mucocutaneous autoimmune skin blistering disease. Several lines of evidence underscore the contribution of autoantibodies against type VII collagen (COL7) to the pathogenesis of EBA. Furthermore, EBA susceptibility is associated with the MHC haplotype in patients (HLA-DR2) and in immunization-induced EBA in mice (H2s). The latter study indicated an additional contribution of non-MHC genes to disease susceptibility. To identify non-MHC genes controlling EBA susceptibility, we intercrossed EBA-susceptible MRL/MpJ with EBA-resistant NZM2410/J and BXD2/TyJ as well as Cast mice. Mice of the fourth generation of this four-way autoimmune-prone advanced intercross line were immunized with a fragment of murine COL7 to induce EBA. Anti-COL7 autoantibodies were detected in 84% of mice, whereas deposition of complement at the dermal-epidermal junction (DEJ) was observed in 50% of the animals; 33% of immunized mice presented with overt clinical EBA. Onset of clinical disease was associated with several quantitative trait loci (QTLs) located on chromosomes 9, 12, 14, and 19, whereas maximum disease severity was linked to QTLs on chromosomes 1, 15, and 19. This more detailed insight into the pathogenesis of EBA may eventually lead to new treatment strategies for EBA and other autoantibody-mediated diseases.

Experimental use of mouse models of systemic lupus erythematosus

Mouse models of lupus have for many years provided accessible and reliable research systems for the pathogenesis and therapy of systemic autoimmune disease, spanning a spectrum of inbred strains that develop spontaneous disease to experimentally induced, sometimes genetically manipulated animals. Nearly all the models share in common the development of glomerulonephritis and autoantibodies, including antinuclear and DNA specificities, the most common endpoints examined in experimental studies, but exhibit specific differences in the incidence of other end-organ manifestations such as hemolytic anemia, arthritis, dermatitis, and vasculitis. This chapter contrasts the clinical characteristics of these various models, providing an outline for their use and analysis.

Characterization of a scavenger receptor cysteine-rich-domain-containing protein of the starfish, Asterina pectinifera: ApSRCR1 acts as an opsonin in the larval and adult innate immune systems

Proteins containing a scavenger receptor cysteine-rich (SRCR) domain (SRCR proteins) play an important role in the innate immune system of various metazoan animals. In the starfish Asterina pectinifera, mesenchyme cells and coelomocytes govern the two distinct innate immune systems of the larvae and adults, respectively. Here we identify a cDNA encoding a protein containing nine SRCR domains termed ApSRCR1, and present characterization of the molecular structure, expression, subcellular localization and function of ApSRCR1 protein during ontogenesis of this animal. ApSRCR1 protein is a membrane-type protein with a predicted molecular mass of approximately 120 kDa. During ontogenesis, ApSRCR1 protein is de novo synthesized and localizes to cytoplasmic vesicles in both mesenchyme cells and coelomocytes without translation of maternal mRNA; however, the net production and modification by N-glycosylation of ApSRCR1 protein differs in each cell type. In both types of cell, functional inhibition of ApSRCR1 protein leads to incompetent bacterial clearance and failure of aggregate formation. However, this inhibitory effect is weaker in the mesenchyme cells than in the coelomocytes. In the bacteria-sensitized adult, ApSRCR1 protein is up-regulated and digested to enable its secretion into the coelomic fluid. This secreted form of ApSRCR1 protein can apparently bind to bacteria. Overall, we show that ApSRCR1 protein is finely regulated for expression not only during development but also in a sensitive innate immunological situation, and thereupon acts as an opsonin for bacteria to different extents in the larvae and adults of A. pectinifera.

Genetics and the environment converge to dysregulate N-glycosylation in multiple sclerosis

How environmental factors combine with genetic risk at the molecular level to promote complex trait diseases such as multiple sclerosis (MS) is largely unknown. In mice, N-glycan branching by the Golgi enzymes Mgat1 and/or Mgat5 prevents T cell hyperactivity, cytotoxic T-lymphocyte antigen 4 (CTLA-4) endocytosis, spontaneous inflammatory demyelination and neurodegeneration, the latter pathologies characteristic of MS. Here we show that MS risk modulators converge to alter N-glycosylation and/or CTLA-4 surface retention conditional on metabolism and vitamin D₃, including genetic variants in interleukin-7 receptor-α (IL7RA*C), interleukin-2 receptor-α (IL2RA*T), MGAT1 (IV_AV_T−T) and CTLA-4 (Thr17Ala). Downregulation of Mgat1 by IL7RA*C and IL2RA*T is opposed by MGAT1 (IV_AV_T−T) and vitamin D₃, optimizing branching and mitigating MS risk when combined with enhanced CTLA-4 N-glycosylation by CTLA-4 Thr17. Our data suggest a molecular mechanism in MS whereby multiple environmental and genetic inputs lead to dysregulation of a final common pathway, namely N-glycosylation.

Complex diseases such as multiple sclerosis have both genetic and environmental components. This study demonstrates that variants of genes implicated in multiple sclerosis, and alterations in cellular metabolism and vitamin D3 levels, alter N-glycosylation, a post-translational modification causal of the disease in mice.

Mgat5 deficiency in T cells and experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an inflammatory demyelinating and neurodegenerative disease initiated by autoreactive T cells. Mgat5, a gene in the Asn (N-) linked protein glycosylation pathway, associates with MS severity and negatively regulates experimental autoimmune encephalomyelitis (EAE) and spontaneous inflammatory demyelination in mice. N-glycan branching by Mgat5 regulates interaction of surface glycoproteins with galectins, forming a molecular lattice that differentially controls the concentration of surface glycoproteins. T-cell receptor signaling, T-cell proliferation, T_H1 differentiation, and CTLA-4 endocytosis are inhibited by Mgat5 branching. Non-T cells also contribute to MS pathogenesis and express abundant Mgat5 branched N-glycans. Here we explore whether Mgat5 deficiency in myelin-reactive T cells is sufficient to promote demyelinating disease. Adoptive transfer of myelin-reactive Mgat5^−/− T cells into Mgat5^+/+ versus Mgat5^−/− recipients revealed more severe EAE in the latter, suggesting that Mgat5 branching deficiency in recipient naive T cells and/or non-T cells contribute to disease pathogenesis.

Genome-wide evolutionary conservation of N-glycosylation sites

Although posttranslational protein modifications are generally thought to perform important cellular functions, recent studies showed that a large fraction of phosphorylation sites are not evolutionarily conserved. Whether the same is true for other protein modifications, such as N-glycosylation is an open question. N-glycosylation is a form of cotranslational and posttranslational modification that occurs by enzymatic addition of a polysaccharide, or glycan, to an asparagine (N) residue of a protein. Examining a large set of experimentally determined mouse N-glycosylation sites, we find that the evolutionary rate of glycosylated asparagines is significantly lower than that of nonglycosylated asparagines of the same proteins. We further confirm that the conservation of glycosylated asparagines is accompanied by the conservation of the canonical motif sequence for glycosylation, suggesting that the above substitution rate difference is related to glycosylation. Interestingly, when solvent accessibility is considered, the substitution rate disparity between glycosylated and nonglycosylated asparagines is highly significant at solvent accessible sites but not at solvent inaccessible sites. Thus, although the solvent inaccessible glycosylation sites were experimentally identified, they are unlikely to be genuine or physiologically important. For solvent accessible asparagines, our analysis reveals a widespread and strong functional constraint on glycosylation, unlike what has been observed for phosphorylation sites in most studies, including our own analysis. Because the majority of N-glycosylation occurs at solvent accessible sites, our results show an overall functional importance for N-glycosylation.

Cytokine-dependent but acquired immunity-independent arthritis caused by DNA escaped from degradation

DNase II digests the chromosomal DNA in macrophages after apoptotic cells and nuclei from erythroid precursors are engulfed. The DNase II-null mice develop a polyarthritis that resembles rheumatoid arthritis. Here, we showed that when bone marrow cells from the DNase II-deficient mice were transferred to the wild-type mice, they developed arthritis. A deficiency of Rag2 or a lack of lymphocytes accelerated arthritis of the DNase II-null mice, suggesting that the DNase II(-/-) macrophages were responsible for triggering arthritis, and their lymphocytes worked protectively. A high level of TNFα, IL-1β, and IL-6 was found in the affected joints of the DNase II-null mice, suggesting an inflammatory-skewed cytokine storm was established in the joints. A lack of TNFα, IL-1β, or IL-6 gene blocked the expression of the other cytokine genes as well and inhibited the development of arthritis. Neutralization of TNFα, IL-1β, or IL-6 had a therapeutic effect on the developed arthritis of the DNase II-null mice, indicating that the cytokine storm was essential for the maintenance of arthritis in the DNase II-deficient mice. Methotrexate, an antimetabolite that is often used to treat patients with rheumatoid arthritis, had a therapeutic effect with the DNase II-null mice. These properties of arthritis in the DNase II-null mice were similar to those found in human systemic-onset juvenile idiopathic arthritis or Still's disease, indicating that the DNase II-null mice are a good animal model of this type of arthritis.

Naturally occurring glycan forms of human immunoglobulins G1 and G2

High resolution glycan mapping was performed on human immunoglobulin G (IgG) obtained from individual healthy subjects and from a combined sample of healthy subjects. In addition to the commonly known complex glycans, a variety of minor glycans are described and quantified, including high mannose forms and several previously unreported hybrid forms. Fc specific glycan analysis was also performed through peptide mapping with LC/MS/MS. Differences in the glycan linked Fc peptide masses allowed glycan profiles to be analyzed and quantified from IgG1 and IgG2 simultaneously for each subject within the same sample. Glycan profiles differed between subtypes, with greater levels of more fully galactosylated species found on IgG1 (e.g. G2F, SG2F) than IgG2. These results also show that Gal attachment on G1F is biased to the Man (alpha1-->6) arm for IgG1 and on the Man (alpha1-->3) arm for IgG2 from individual healthy subjects.

Blockade of Notch1 signaling alleviates murine lupus via blunting macrophage activation and M2b polarization

Patients with systemic lupus erythematosus (SLE) are found to be accompanied with innate immunity dysregulation including abnormally macrophage activation. But the functional polarization of the activated macrophages and its underlying molecular mechanism during the pathogenesis of SLE remains unknown. As an important local cellular interaction mechanism responsible for cell fate determination, Notch signaling is reported to exert crucial functions in the development and differentiation of various immunocytes, whereas its role in macrophage polarization is not fully understood. In this study, in the SLE murine model generated by immunization with activated lymphocyte-derived DNA (ALD-DNA), infiltrated macrophages in the nephritic tissues were found to exhibit activation and M2b functional polarization. Notch1 signaling activity was significantly upregulated in the ALD-DNA-induced M2b macrophages in vitro and in vivo. Furthermore, ALD-DNA-induced M2b polarization was found to be dependent on enhanced Notch1 signaling through accelerating NF-kappaB p50 translocation into the nucleus mediated by PI3K and MAPK pathways. Moreover, blockade of Notch1 signaling with gamma-secretase inhibitor treatment before or after the disease initiation could ameliorate murine lupus through impeding macrophage M2b polarization. Our results implied that Notch1 signaling-dependent macrophage M2b polarization might play a pivotal role in the pathogenesis of SLE, which could provide Notch1 signaling blockade as a potential therapeutic approach for SLE disease.

Mannose receptor interacts with Fc receptors and is critical for the development of crescentic glomerulonephritis in mice

Crescentic glomerulonephritis (CGN), which frequently results in acute and chronic kidney disease, is characterized by and dependent on glomerular infiltration by macrophages. The mannose receptor (MR) is a pattern recognition receptor implicated in the uptake of endogenous and microbial ligands by macrophages, mesangial cells (MCs), and selected endothelial cells. It is upregulated on alternatively activated macrophages (i.e., macrophages associated with tissue repair and humoral immunity) and involved in antigen presentation to T cells. We used the mouse model of nephrotoxic nephritis to investigate the role of MR in CGN. Our results demonstrate what we believe to be a novel role for MR in the promotion of CGN that is independent of adaptive immune responses. MR-deficient (Mr-/-) mice were protected from CGN despite generating humoral and T cell responses similar to those of WT mice, but they demonstrated diminished macrophage and MC Fc receptor-mediated (FcR-mediated) functions, including phagocytosis and Fc-mediated oxygen burst activity. Mr-/- MCs demonstrated augmented apoptosis compared with WT cells, and this was associated with diminished Akt phosphorylation. Macrophage interaction with apoptotic MCs induced a noninflammatory phenotype that was more marked in Mr-/- macrophages than in WT macrophages. Our results demonstrate that MR augments Fc-mediated function and promotes MC survival. We suggest that targeting MR may provide an alternative therapeutic approach in CGN while minimizing the impact on adaptive immune responses, which are affected by conventional immunosuppressive approaches.

Liver membrane proteome glycosylation changes in mice bearing an extra-hepatic tumor

Cancer is well known to be associated with alterations in membrane protein glycosylation (Bird, N. C., Mangnall, D., and Majeed, A. W. (2006) Biology of colorectal liver metastases: A review. J. Surg. Oncol. 94, 68-80; Dimitroff, C. J., Pera, P., Dall'Olio, F., Matta, K. L., Chandrasekaran, E. V., Lau, J. T., and Bernacki, R. J. (1999) Cell surface n-acetylneuraminic acid alpha2,3-galactoside-dependent intercellular adhesion of human colon cancer cells. Biochem. Biophys. Res. Commun. 256, 631-636; and Arcinas, A., Yen, T. Y., Kebebew, E., and Macher, B. A. (2009) Cell surface and secreted protein profiles of human thyroid cancer cell lines reveal distinct glycoprotein patterns. J. Proteome Res. 8, 3958-3968). Equally, it has been well established that tumor-associated inflammation through the release of pro-inflammatory cytokines is a common cause of reduced hepatic drug metabolism and increased toxicity in advanced cancer patients being treated with cytotoxic chemotherapies. However, little is known about the impact of bearing a tumor (and downstream effects like inflammation) on liver membrane protein glycosylation. In this study, proteomic and glycomic analyses were used in combination to determine whether liver membrane protein glycosylation was affected in mice bearing the Engelbreth-Holm Swarm sarcoma. Peptide IPG-IEF and label-free quantitation determined that many enzymes involved in the protein glycosylation pathway specifically; mannosidases (Man1a-I, Man1b-I and Man2a-I), mannoside N-acetylglucosaminyltransferases (Mgat-I and Mgat-II), galactosyltransferases (B3GalT-VII, B4GalT-I, B4GalT-III, C1GalT-I, C1GalT-II, and GalNT-I), and sialyltransferases (ST3Gal-I, ST6Gal-I, and ST6GalNAc-VI) were up-regulated in all livers of tumor-bearing mice (n = 3) compared with nontumor bearing controls (n = 3). In addition, many cell surface lectins: Sialoadhesin-1 (Siglec-1), C-type lectin family 4f (Kupffer cell receptor), and Galactose-binding lectin 9 (Galectin-9) were determined to be up-regulated in the liver of tumor-bearing compared with control mice. Global glycan analysis identified seven N-glycans and two O-glycans that had changed on the liver membrane proteins derived from tumor-bearing mice. Interestingly, α (2,3) sialic acid was found to be up-regulated on the liver membrane of tumor-bearing mice, which reflected the increased expression of its associated sialyltransferase and lectin receptor (siglec-1). The overall increased sialylation on the liver membrane of Engelbreth-Holm Swarm bearing mice correlates with the increased expression of their associated glycosyltransferases and suggests that glycosylation of proteins in the liver plays a role in tumor-induced liver inflammation.

Glycosylation: An intrinsic sign of "danger"

The "danger" model of immunity posits that the immune system is triggered by endogenous danger signals, rather than exogenous non-self signals per se. It has been proposed that danger signals may consist of both intracellular "pre-packed" molecules released from damaged cells and stress-induced proteins. Here we focus on glycosylation aberrancies as a unifying concept for danger signaling. According to this proposition glycosylation patterns reliably reflect cellular phenotypic state and appearance of altered carbohydrate structures may constitute a pivotal phenotypic alteration that alarms the immune system to danger and initiates immunity. Viewed from this vantage point, healthy cells avert immune recognition by virtue of their normal terminal glycosylation patterns. By contrast, abnormal cells display and release glycoproteins and glycolipids with aberrant terminal glycosylation trees, which in turn immunologically flag these cells. Diverse carbohydrate-binding receptors are expressed on immune cells and are used to detect these phenotypic changes. Thus, in addition to the "pre-packed" and stress-induced signals this glycosylation-based signal represents an endogenous signal reliably reflecting the cell phenotypic status, enabling the immune system to monitor the tissue/cell's physical condition and to respond accordingly.

Decreased expression of Fli-1 in bone marrow-derived haematopoietic cells significantly affects disease development in Murphy Roths Large/lymphoproliferation (MRL/lpr) mice

The transcription factor Fli-1 is implicated in the pathogenesis of both murine and human lupus. Decreased expression of Fli-1 in heterozygous (Fli-1(+/-)) Murphy Roths Large (MRL)/lpr mice resulted in significantly lower kidney pathological scores and markedly increased survival. In this study, bone marrow (BM) transplantation was used to investigate the role of decreased expression of Fli-1 in haematopoietic versus non-haematopoietic cell lineages in autoimmune disease development. Wild-type (WT) MRL/lpr that received BM from Fli-1(+/-) MRL/lpr mice had statistically significantly lower autoantibodies, less proteinuria, reduced renal disease and prolonged survival compared to WT MRL/lpr mice that received BM from WT MRL/lpr mice. Although not statistically significant, Fli-1(+/-) MRL/lpr mice that received BM from WT MRL/lpr mice also had lower autoantibodies and improved survival compared to WT MRL/lpr mice that received BM from WT MRL/lpr mice. Our data indicate that expression of Fli-1 in haematopoietic cell lineages has a significant effect on disease development in MRL/lpr mice.

Endogenous ligands for C-type lectin receptors: the true regulators of immune homeostasis

C-type lectin receptors (CLRs) have long been known as pattern-recognition receptors implicated in the recognition of pathogens by the innate immune system. However, evidence is accumulating that many CLRs are also able to recognize endogenous 'self' ligands and that this recognition event often plays an important role in immune homeostasis. In the present review, we focus on the human and mouse CLRs for which endogenous ligands have been described. Special attention is given to the signaling events initiated upon recognition of the self ligand and the regulation of glycosylation as a switch modulating CLR recognition, and therefore, immune homeostasis.

A human embryonic kidney 293T cell line mutated at the Golgi alpha-mannosidase II locus

Disruption of Golgi alpha-mannosidase II activity can result in type II congenital dyserythropoietic anemia and induce lupus-like autoimmunity in mice. Here, we isolated a mutant human embryonic kidney (HEK) 293T cell line called Lec36, which displays sensitivity to ricin that lies between the parental HEK 293T cells, in which the secreted and membrane-expressed proteins are dominated by complex-type glycosylation, and 293S Lec1 cells, which produce only oligomannose-type N-linked glycans. Stem cell marker 19A was transiently expressed in the HEK 293T Lec36 cells and in parental HEK 293T cells with and without the potent Golgi alpha-mannosidase II inhibitor, swainsonine. Negative ion nano-electrospray ionization mass spectra of the 19A N-linked glycans from HEK 293T Lec36 and swainsonine-treated HEK 293T cells were qualitatively indistinguishable and, as shown by collision-induced dissociation spectra, were dominated by hybrid-type glycosylation. Nucleotide sequencing revealed mutations in each allele of MAN2A1, the gene encoding Golgi alpha-mannosidase II: a point mutation that mapped to the active site was found in one allele, and an in-frame deletion of 12 nucleotides was found in the other allele. Expression of the wild type but not the mutant MAN2A1 alleles in Lec36 cells restored processing of the 19A reporter glycoprotein to complex-type glycosylation. The Lec36 cell line will be useful for expressing therapeutic glycoproteins with hybrid-type glycans and as a sensitive host for detecting mutations in human MAN2A1 causing type II congenital dyserythropoietic anemia.