Targeting Siglecs with a sialic acid-decorated nanoparticle abrogates inflammation

A sweet spot for macrophages: Focusing on polarization

Macrophages are a type of functionally plastic cells that can create a pro-/anti-inflammatory microenvironment for organs by producing different kinds of cytokines, chemokines, and growth factors to regulate immunity and inflammatory responses. In addition, they can also be induced to adopt different phenotypes in response to extracellular and intracellular signals, a process defined as M1/M2 polarization. Growing evidence indicates that glycobiology is closely associated with this polarization process. In this research, we review studies of the roles of glycosylation, glucose metabolism, and key lectins in the regulation of macrophages function and polarization to provide a new perspective for immunotherapies for multiple diseases.

Nanomedicine-Based Therapeutics to Combat Acute Lung Injury

Acute lung injury (ALI) or its aggravated stage acute respiratory distress syndrome (ARDS) may lead to a life-threatening form of respiratory failure, resulting in high mortality of up to 30-40% in most studies. Although there have been decades of research since ALI was first described in 1967, the clinical therapeutic alternatives for ALI are still in a state of limited availability. Supportive treatment and mechanical ventilation still have priority. Despite some preclinical studies demonstrating the benefit of pharmacological interventions, none of these has been proved completely effective to date. Recent advances in nanotechnology may shed new light on the pharmacotherapy of ALI. Nanomedicine possesses targeting and synergistic therapeutic capability, thus boosting pharmaceutical efficacy and mitigating the side effects. Currently, a variety of nanomedicine with diverse frameworks and functional groups have been elaborately developed, in accordance with their lung targeting ability and the pathophysiology of ALI. The in-depth review of the current literature reveals that liposomes, polymers, inorganic materials, cell membranes, platelets, and other nanomedicine approaches have conferred attractive therapeutic benefits for ALI treatment. In this review, we explore the recent progress in the study of the nanomedicine-based therapy of ALI, presenting various nanomedical approaches, drug choices, therapeutic strategies, and outcomes, thereby providing insight into the trends.

The clinical impact of glycobiology: targeting selectins, Siglecs and mammalian glycans

Carbohydrates - namely glycans - decorate every cell in the human body and most secreted proteins. Advances in genomics, glycoproteomics and tools from chemical biology have made glycobiology more tractable and understandable. Dysregulated glycosylation plays a major role in disease processes from immune evasion to cognition, sparking research that aims to target glycans for therapeutic benefit. The field is now poised for a boom in drug development. As a harbinger of this activity, glycobiology has already produced several drugs that have improved human health or are currently being translated to the clinic. Focusing on three areas - selectins, Siglecs and glycan-targeted antibodies - this Review aims to tell the stories behind therapies inspired by glycans and to outline how the lessons learned from these approaches are paving the way for future glycobiology-focused therapeutics.

The Role of Siglec-G on Immune Cells in Sepsis

Sepsis is a life-threatening clinical syndrome that results from an overwhelming immune response to infection. During sepsis, immune cells are activated by sensing pathogen-associated molecular patterns and damage-associated molecular patterns (DAMPs) through pattern recognizing receptors (PRRs). Regulation of the immune response is essential to preventing or managing sepsis. Sialic acid-binding immunoglobulin-type lectin-G (Siglec-G), a CD33 group of Siglec expressed in B-1a cells and other hematopoietic cells, plays an important immunoregulatory role. B-1a cells, a subtype of B lymphocytes, spontaneously produce natural IgM which confers protection against infection. B-1a cells also produce IL-10, GM-CSF, and IL-35 to control inflammation. Sialic acids are present on cell membranes, receptors, and glycoproteins. Siglec-G binds to the sialic acid residues on the B cell receptor (BCR) and controls BCR-mediated signal transduction, thereby maintaining homeostasis of Ca⁺⁺ influx and NFATc1 expression. Siglec-G inhibits NF-κB activation in B-1a cells and regulates B-1a cell proliferation. In myeloid cells, Siglec-G inhibits DAMP-mediated inflammation by forming a ternary complex with DAMP and CD24. Thus, preserving Siglec-G’s function could be a novel therapeutic approach in sepsis. Here, we review the immunoregulatory functions of Siglec-G in B-1a cells and myeloid cells in sepsis. A clear understanding of Siglec-G is important to developing novel therapeutics in treating sepsis.

Tolerogenic Immunotherapy: Targeting DC Surface Receptors to Induce Antigen-Specific Tolerance

Dendritic cells (DCs) are well-established as major players in the regulation of immune responses. They either induce inflammatory or tolerogenic responses, depending on the DC-subtype and stimuli they receive from the local environment. This dual capacity of DCs has raised therapeutic interest for their use to modify immune-activation via the generation of tolerogenic DCs (tolDCs). Several compounds such as vitamin D3, retinoic acid, dexamethasone, or IL-10 and TGF-β have shown potency in the induction of tolDCs. However, an increasing interest exists in defining tolerance inducing receptors on DCs for new targeting strategies aimed to develop tolerance inducing immunotherapies, on which we focus particular in this review. Ligation of specific cell surface molecules on DCs can result in antigen presentation to T cells in the presence of inhibitory costimulatory molecules and tolerogenic cytokines, giving rise to regulatory T cells. The combination of factors such as antigen structure and conformation, delivery method, and receptor specificity is of paramount importance. During the last decades, research provided many tools that can specifically target various receptors on DCs to induce a tolerogenic phenotype. Based on advances in the knowledge of pathogen recognition receptor expression profiles in human DC subsets, the most promising cell surface receptors that are currently being explored as possible targets for the induction of tolerance in DCs will be discussed. We also review the different strategies that are being tested to target DC receptors such as antigen-carbohydrate conjugates, antibody-antigen fusion proteins and antigen-adjuvant conjugates.

The human sialic acid-binding immunoglobulin-like lectin Siglec-9 and its murine homolog Siglec-E control osteoclast activity and bone resorption

Regulation of osteoclast differentiation and function is a central element in bone homeostasis. While the role of soluble factors, such as cytokines, hormones and growth factors, in controlling osteoclast differentiation has been intensively characterized, the function of surface receptors is less well understood. Sialic acid-binding immunoglobulin-like lectin (Siglec)-9 and its murine homolog Siglec-E are sialic acid-recognizing inhibitory receptors from the CD33-related Siglec-family and mainly expressed on myeloid cells. We found Siglec-9 and Siglec-E to be expressed at all stages of human and murine osteoclastogenesis, respectively. Siglec-E knockout mice displayed lower bone mass despite unchanged osteoclast numbers and an increased bone formation rate. Ex vivo osteoclast assays using Siglec-E knockout cells or a blocking antibody against human Siglec-9 confirmed the suppressive effect of Siglec-9/Siglec-E on osteoclast function. Although osteoclast numbers were unchanged or even slightly decreased, the blockade/absence of Siglec-9/Siglec-E resulted in an augmented resorption activity of mature osteoclasts. This increased resorption activity was associated with enlarged actin rings. Together, our results suggest Siglec-9/Siglec-E to inhibit osteoclast activation independently from osteoclast differentiation and thereby propose a new mechanism for the control of local bone resorption.

Human Lectins, Their Carbohydrate Affinities and Where to Find Them

Lectins are a class of proteins responsible for several biological roles such as cell-cell interactions, signaling pathways, and several innate immune responses against pathogens. Since lectins are able to bind to carbohydrates, they can be a viable target for targeted drug delivery systems. In fact, several lectins were approved by Food and Drug Administration for that purpose. Information about specific carbohydrate recognition by lectin receptors was gathered herein, plus the specific organs where those lectins can be found within the human body.

Modulation of immune cell reactivity with cis-binding Siglec agonists

Inflammatory pathologies caused by phagocytes lead to numerous debilitating conditions, including chronic pain and blindness due to age-related macular degeneration. Many members of the sialic acid-binding immunoglobulin-like lectin (Siglec) family are immunoinhibitory receptors whose agonism is an attractive approach for antiinflammatory therapy. Here, we show that synthetic lipid-conjugated glycopolypeptides can insert into cell membranes and engage Siglec receptors in cis, leading to inhibitory signaling. Specifically, we construct a cis-binding agonist of Siglec-9 and show that it modulates mitogen-activated protein kinase (MAPK) signaling in reporter cell lines, immortalized macrophage and microglial cell lines, and primary human macrophages. Thus, these cis-binding agonists of Siglecs present a method for therapeutic suppression of immune cell reactivity.

Advances in sepsis diagnosis and management: a paradigm shift towards nanotechnology

Sepsis, a dysregulated immune response due to life-threatening organ dysfunction, caused by drug-resistant pathogens, is a major global health threat contributing to high disease burden. Clinical outcomes in sepsis depend on timely diagnosis and appropriate early therapeutic intervention. There is a growing interest in the evaluation of nanotechnology-based solutions for sepsis management due to the inherent and unique properties of these nano-sized systems. This review presents recent advancements in nanotechnology-based solutions for sepsis diagnosis and management. Development of nanosensors based on electrochemical, immunological or magnetic principals provide highly sensitive, selective and rapid detection of sepsis biomarkers such as procalcitonin and C-reactive protein and are reviewed extensively. Nanoparticle-based drug delivery of antibiotics in sepsis models have shown promising results in combating drug resistance. Surface functionalization with antimicrobial peptides further enhances efficacy by targeting pathogens or specific microenvironments. Various strategies in nanoformulations have demonstrated the ability to deliver antibiotics and anti-inflammatory agents, simultaneously, have been reviewed. The critical role of nanoformulations of other adjuvant therapies including antioxidant, antitoxins and extracorporeal blood purification in sepsis management are also highlighted. Nanodiagnostics and nanotherapeutics in sepsis have enormous potential and provide new perspectives in sepsis management, supported by promising future biomedical applications included in the review.

Siglec-E retards atherosclerosis by inhibiting CD36-mediated foam cell formation

BACKGROUND

The accumulation of lipid-laden macrophages, foam cells, within sub-endothelial intima is a key feature of early atherosclerosis. Siglec-E, a mouse orthologue of human Siglec-9, is a sialic acid binding lectin predominantly expressed on the surface of myeloid cells to transduce inhibitory signal via recruitment of SH2-domain containing protein tyrosine phosphatase SHP-1/2 upon binding to its sialoglycan ligands. Whether Siglec-E expression on macrophages impacts foam cell formation and atherosclerosis remains to be established.

METHODS

ApoE-deficient (apoE^-/-) and apoE/Siglec-E-double deficient (apoE^-/-/Siglec-E^-/-) mice were placed on high fat diet for 3 months and their lipid profiles and severities of atherosclerosis were assessed. Modified low-density lipoprotein (LDL) uptake and foam cell formation in wild type (WT) and Siglec-E^-/-- peritoneal macrophages were examined in vitro. Potential Siglec-E-interacting proteins were identified by proximity labeling in conjunction with proteomic analysis and confirmed by coimmunoprecipitation experiment. Impacts of Siglec-E expression and cell surface sialic acid status on oxidized LDL uptake and signaling involved were examined by biochemical assays.

RESULTS

Here we show that genetic deletion of Siglec-E accelerated atherosclerosis without affecting lipid profile in apoE^-/- mice. Siglec-E deficiency promotes foam cell formation by enhancing acetylated and oxidized LDL uptake without affecting cholesterol efflux in macrophages in vitro. By performing proximity labeling and proteomic analysis, we identified scavenger receptor CD36 as a cell surface protein interacting with Siglec-E. Further experiments performed in HEK293T cells transiently overexpressing Siglec-E and CD36 and peritoneal macrophages demonstrated that depletion of cell surface sialic acids by treatment with sialyltransferase inhibitor or sialidase did not affect interaction between Siglec-E and CD36 but retarded Siglec-E-mediated inhibition on oxidized LDL uptake. Subsequent experiments revealed that oxidized LDL induced transient Siglec-E tyrosine phosphorylation and recruitment of SHP-1 phosphatase in macrophages. VAV, a downstream effector implicated in CD36-mediated oxidized LDL uptake, was shown to interact with SHP-1 following oxidized LDL treatment. Moreover, oxidized LDL-induced VAV phosphorylation was substantially lower in WT macrophages comparing to Siglec-E^-/- counterparts.

CONCLUSIONS

These data support the protective role of Siglec-E in atherosclerosis. Mechanistically, Siglec-E interacts with CD36 to suppress downstream VAV signaling involved in modified LDL uptake.

Microarray investigation of glycan remodeling during macrophage polarization reveals α2,6 sialic acid as an anti-inflammatory indicator

Glycosylation is a widely occurring posttranslational modification. Here, we applied a quick, convenient and high-throughput strategy (lectin array) to investigate the variation in glycans on different macrophage subtypes derived from THP-1 and RAW264.7 cells. For THP-1 cells, there were more significant differences in the glycan on M2 macrophages compared to the other two subtypes. In contrast, M1 macrophages exhibited more significant glycan remodeling than the other subtypes for the RAW264.7 cell line. The response of the lectins which recogonize the N-glycan and α2,6 sialic acid was higher during polarization into anti-inflammatory phase (THP-1 derived M2 subtypes), and lower in pro-inflammatory phase (RAW264.7 M1 subtypes). The regulation of several α2,6 sialyltransferase genes was coincident with the regulation of the α2,6 sialic acid on the two cell lines. The lectin response and glycosyltranferase gene expression confirmed that α2,6 sialic acid showed higher expression in the anti-inflammatory phase. This indicated that α2,6 sialic acid was a potential indicator for the anti-inflammatory response.

The therapeutic potential of sialylated Fc domains of human IgG

Pathogens frequently use multivalent binding to sialic acid to infect cells or to modulate immunity through interactions with human sialic acid-binding immunoglobulin-type lectins (Siglecs). Molecules that interfere with these interactions could be of interest as diagnostics, anti-infectives or as immune modulators. This review describes the development of molecular scaffolds based on the crystallizable fragment (Fc) region of immunoglobulin (Ig) G that deliver high-avidity binding to innate immune receptors, including sialic acid-dependent receptors. The ways in which the sialylated Fc may be engineered as immune modulators that mimic the anti-inflammatory properties of intravenous polyclonal Ig or as blockers of sialic-acid-dependent infectivity by viruses are also discussed.

Neutrophils and Macrophages as Targets for Development of Nanotherapeutics in Inflammatory Diseases

Neutrophils and macrophages are major components of innate systems, playing central roles in inflammation responses to infections and tissue injury. If they are out of control, inflammation responses can cause the pathogenesis of a wide range of diseases, such as inflammatory disorders and autoimmune diseases. Precisely regulating the functions of neutrophils and macrophages in vivo is a potential strategy to develop immunotherapies to treat inflammatory diseases. Advances in nanotechnology have enabled us to design nanoparticles capable of targeting neutrophils or macrophages in vivo. This review discusses the current status of how nanoparticles specifically target neutrophils or macrophages and how they manipulate leukocyte functions to inhibit their activation for inflammation resolution or to restore their defense ability for pathogen clearance. Finally, we present a novel concept of hijacking leukocytes to deliver nanotherapeutics across the blood vessel barrier. This review highlights the challenges and opportunities in developing nanotherapeutics to target leukocytes for improved treatment of inflammatory diseases.

Neutrophils in respiratory syncytial virus infection: From harmful effects to therapeutic opportunities

Respiratory syncytial virus (RSV) is an important infectious agent in infants and young children. In most cases, RSV infection only causes mild disease, but in some, it requires invasive ventilation. Although antiviral drugs are obvious candidates to treat viral illness, and some have shown antiviral effects in humans, antivirals such as GS-5806, ALX-0171 and ALS-8176 have not yet met their expectations. Since the inappropriate or dysregulated immune response against RSV leads to harmful immune pathology, a robust immune cascade is probably underway by the time patients reach the hospital. RSV infection is associated with a strong neutrophil influx into the airway. It not clear if these cells contribute to antiviral defence or to lung pathology. This article discusses the protective and harmful roles of neutrophils during RSV infection and provides an overview of mechanisms by which neutrophil function could be targeted to prevent tissue injury and preserve homeostasis.

Current Status on Therapeutic Molecules Targeting Siglec Receptors

The sialic acid-binding immunoglobulin-type of lectins (Siglecs) are receptors that recognize sialic acid-containing glycans. In the majority of the cases, Siglecs are expressed on immune cells and play a critical role in regulating immune cell signaling. Over the years, it has been shown that the sialic acid-Siglec axis participates in immunological homeostasis, and that any imbalance can trigger different pathologies, such as autoimmune diseases or cancer. For all this, different therapeutics have been developed that bind to Siglecs, either based on antibodies or being smaller molecules. In this review, we briefly introduce the Siglec family and we compile a description of glycan-based molecules and antibody-based therapies (including CAR-T and bispecific antibodies) that have been designed to therapeutically targeting Siglecs.

Tools to study and target the Siglec-sialic acid axis in cancer

Siglecs are widely expressed on leucocytes and bind to ubiquitously presented glycans containing sialic acids (sialoglycans). Most Siglecs carry an immunoreceptor tyrosine-based inhibition motif (ITIM) and elicit an inhibitory intracellular signal upon ligand binding. A few Siglec receptors can, however, recruit immunoreceptor tyrosine-based activation motif (ITAM)-containing factors, which activate cells. The role of hypersialylation (the enhanced expression of sialoglycans) has recently been explored in cancer progression. Mechanistic studies have shown that hypersialylation on cancer cells can engage inhibitory Siglecs on the surface of immune cells and induce immunosuppression. These recent studies strongly suggest that the Siglec-sialic acid axis can act as a potential target for cancer immunotherapy. Moreover, the use of new tools and techniques is facilitating these studies. In this review, we summarise techniques used to study Siglecs, including different mouse models, monoclonal antibodies, Siglec fusion proteins, and sialoglycan arrays. Furthermore, we discuss the recent major developments in the study of Siglecs in cancer immunosuppression, tools, and techniques used in targeting the Siglec-sialic acid axis and the possibility of clinical intervention.

Biomedical nanomaterials for immunological applications: ongoing research and clinical trials

Research efforts on nanomaterial-based therapies for the treatment of autoimmune diseases and cancer have spiked and have made rapid progress over the past years. Nanomedicine has been shown to contribute significantly to overcome current therapeutic limitations, exhibiting advantages compared to conventional therapeutics, such as sustained drug release, delayed drug degradation and site-specific drug delivery. Multiple nanodrugs have reached the clinic, but translation is often hampered by either low targeting efficiency or undesired side effects. Nanomaterials, and especially inorganic nanoparticles, have gained criticism due to their potential toxic effects, including immunological alterations. However, many strategies have been attempted to improve the therapeutic efficacy of nanoparticles and exploit their unique properties for the treatment of inflammation and associated diseases. In this review, we elaborate on the immunomodulatory effects of nanomaterials, with a strong focus on the underlying mechanisms that lead to these specific immune responses. Nanomaterials to be discussed include inorganic nanoparticles such as gold, silica and silver, as well as organic nanomaterials such as polymer-, dendrimer-, liposomal- and protein-based nanoparticles. Furthermore, various approaches for tuning nanomaterials in order to enhance their efficacy and attenuate their immune stimulation or suppression, with respect to the therapeutic application, are described. Additionally, we illustrate how the acquired insights have been used to design immunotherapeutic strategies for a variety of diseases. The potential of nanomedicine-based therapeutic strategies in immunotherapy is further illustrated by an up to date overview of current clinical trials. Finally, recent efforts into enhancing immunogenic cell death through the use of nanoparticles are discussed.

High-throughput multiplex assays with mouse macrophages on pillar plate platforms

It is challenging to rapidly identify immune responses that reflect the state and capability of immune cells due to complex heterogeneity of immune cells and their plasticity to pathogens and modulating molecules. Thus, high-throughput and easy-to-use cell culture and analysis platforms are highly desired for characterizing complex immune responses and elucidating their underlying mechanisms as well. In response to this need, we have developed a micropillar chip and a 384-pillar plate, printed mouse macrophage, RAW 264.7 cell line in alginate on the pillar plate platforms, and established multiplex cell-based assays to rapidly measure cell viability, expression of cell surface markers, and secretion of cytokines upon stimulation with model compound, lipopolysaccharide (LPS), as well as synthetic N-glycan polymers that mimic native glycoconjugates and could bind to lectin receptors on RAW 264.7 cells. Interestingly, changes in RAW 264.7 cell viability, expression levels of cell surface makers, and release of cytokines measured from the pillar plate platforms in the presence and absence of LPS were well correlated with those obtained from their counterpart, the 96-well plate with 2D-cultured macrophages. With this approach, we identified that α2,3-linked N-sialyllactose polymer has significant macrophage modulation activity among the N-glycan polymers tested. Therefore, we successfully demonstrated that our pillar plate platforms with 3D-cultured macrophages can streamline immune cell imaging and analysis in high throughput in response to compound stimulation. We envision that the pillar plate platforms could potentially be used for rapid characterization of immune cell responses and for screening immune cell-modulating molecules.

Interferon-α alters host glycosylation machinery during treated HIV infection

Background

A comprehensive understanding of host factors modulated by the antiviral cytokine interferon-α (IFNα) is imperative for harnessing its beneficial effects while avoiding its detrimental side-effects during HIV infection. Cytokines modulate host glycosylation which plays a critical role in mediating immunological functions. However, the impact of IFNα on host glycosylation has never been characterized.

Methods

We assessed the impact of pegylated IFNα2a on IgG glycome, as well as CD8⁺ T and NK cell-surface glycomes, of 18 HIV-infected individuals on suppressive antiretroviral therapy. We linked these glycomic signatures to changes in inflammation, CD8⁺ T and NK cell phenotypes, and HIV DNA.

Findings

We identified significant interactions that support a model in which a) IFNα increases the proportion of pro-inflammatory, bisecting GlcNAc glycans (known to enhance FcγR binding) within the IgG glycome, which in turn b) increases inflammation, which c) leads to poor CD8⁺ T cell phenotypes and poor IFNα-mediated reduction of HIV DNA. Examining cell-surface glycomes, IFNα increases levels of the immunosuppressive GalNAc-containing glycans (T/Tn antigens) on CD8⁺ T cells. This induction is associated with lower HIV-gag-specific CD8⁺ T cell functions. Last, IFNα increases levels of fucose on NK cells. This induction is associated with higher NK functions upon K562 stimulation.

Interpretation

IFNα causes host glycomic alterations that are known to modulate immunological responses. These alterations are associated with both detrimental and beneficial consequences of IFNα. Manipulating host glycomic interactions may represent a strategy for enhancing the positive effects of IFNα while avoiding its detrimental side-effects.

Funding

NIH grants R21AI143385, U01AI110434.

Biomaterial-Driven Immunomodulation: Cell Biology-Based Strategies to Mitigate Severe Inflammation and Sepsis

Inflammation is an essential component of a wide variety of disease processes and oftentimes can increase the deleterious effects of a disease. Finding ways to modulate this essential immune process is the basis for many therapeutics under development and is a burgeoning area of research for both basic and translational immunology. In addition to developing therapeutics for cellular and molecular targets, the use of biomaterials to modify innate and adaptive immune responses is an area that has recently sparked significant interest. In particular, immunomodulatory activity can be engineered into biomaterials to elicit heightened or dampened immune responses for use in vaccines, immune tolerance, or anti-inflammatory applications. Importantly, the inherent physicochemical properties of the biomaterials play a significant role in determining the observed effects. Properties including composition, molecular weight, size, surface charge, and others affect interactions with immune cells (i.e., nano-bio interactions) and allow for differential biological responses such as activation or inhibition of inflammatory signaling pathways, surface molecule expression, and antigen presentation to be encoded. Numerous opportunities to open new avenues of research to understand the ways in which immune cells interact with and integrate information from their environment may provide critical solutions needed to treat a variety of disorders and diseases where immune dysregulation is a key inciting event. However, to elicit predictable immune responses there is a great need for a thorough understanding of how the biomaterial properties can be tuned to harness a designed immunological outcome. This review aims to systematically describe the biological effects of nanoparticle properties-separate from additional small molecule or biologic delivery-on modulating innate immune cell responses in the context of severe inflammation and sepsis. We propose that nanoparticles represent a potential polypharmacological strategy to simultaneously modify multiple aspects of dysregulated immune responses where single target therapies have fallen short for these applications. This review intends to serve as a resource for immunology labs and other associated fields that would like to apply the growing field of rationally designed biomaterials into their work.

Polysialic acid and Siglec-E orchestrate negative feedback regulation of microglia activation

Polysialic acid (polySia) emerges as a novel regulator of microglia activity. We recently identified polysialylated proteins in the Golgi compartment of murine microglia that are released in response to inflammatory stimulation. Since exogenously added polySia is able to attenuate the inflammatory response, we proposed that the release of polysialylated proteins constitutes a mechanism for negative feedback regulation of microglia activation. Here, we demonstrate that translocation of polySia from the Golgi to the cell surface can be induced by calcium depletion of the Golgi compartment and that polysialylated proteins are continuously released for at least 24 h after the onset of inflammatory stimulation. The latter was unexpected, because polySia signals detected by immunocytochemistry are rapidly depleted. However, it indicates that the amount of released polySia is much higher than anticipated based on immunostaining. This may be crucial for microglial responses during traumatic brain injury (TBI), as we detected polySia signals in activated microglia around a stab wound in the adult mouse brain. In BV2 microglia, the putative polySia receptor Siglec-E is internalized during lipopolysaccharide (LPS)-induced activation and in response to polySia exposure, indicating interaction. Correspondingly, CRISPR/Cas9-mediated Siglec-E knockout prevents inhibition of pro inflammatory activation by exogenously added polySia and leads to a strong increase of the LPS response. A comparable increase of LPS-induced activation has been observed in microglia with abolished polySia synthesis. Together, these results indicate that the release of the microglia-intrinsic polySia pool, as implicated in TBI, inhibits the inflammatory response by acting as a trans-activating ligand of Siglec-E.

Sepsis in the era of data-driven medicine: personalizing risks, diagnoses, treatments and prognoses

Sepsis is a series of clinical syndromes caused by the immunological response to infection. The clinical evidence for sepsis could typically attribute to bacterial infection or bacterial endotoxins, but infections due to viruses, fungi or parasites could also lead to sepsis. Regardless of the etiology, rapid clinical deterioration, prolonged stay in intensive care units and high risk for mortality correlate with the incidence of sepsis. Despite its prevalence and morbidity, improvement in sepsis outcomes has remained limited. In this comprehensive review, we summarize the current landscape of risk estimation, diagnosis, treatment and prognosis strategies in the setting of sepsis and discuss future challenges. We argue that the advent of modern technologies such as in-depth molecular profiling, biomedical big data and machine intelligence methods will augment the treatment and prevention of sepsis. The volume, variety, veracity and velocity of heterogeneous data generated as part of healthcare delivery and recent advances in biotechnology-driven therapeutics and companion diagnostics may provide a new wave of approaches to identify the most at-risk sepsis patients and reduce the symptom burden in patients within shorter turnaround times. Developing novel therapies by leveraging modern drug discovery strategies including computational drug repositioning, cell and gene-therapy, clustered regularly interspaced short palindromic repeats -based genetic editing systems, immunotherapy, microbiome restoration, nanomaterial-based therapy and phage therapy may help to develop treatments to target sepsis. We also provide empirical evidence for potential new sepsis targets including FER and STARD3NL. Implementing data-driven methods that use real-time collection and analysis of clinical variables to trace, track and treat sepsis-related adverse outcomes will be key. Understanding the root and route of sepsis and its comorbid conditions that complicate treatment outcomes and lead to organ dysfunction may help to facilitate identification of most at-risk patients and prevent further deterioration. To conclude, leveraging the advances in precision medicine, biomedical data science and translational bioinformatics approaches may help to develop better strategies to diagnose and treat sepsis in the next decade.

A thin hydrogel barrier linked onto cell surface sialic acids through covalent bonds induces cancer cell death in vivo

Hypersialylation is the aberrant expression of sialic acid in cell surface glycans and is pervasive in cancer cells. Recent studies have shown that hypersialylation provides a microenvironment conducive to cancer progression, mediated by the interaction between sialic acid and sialic acid-binding receptors. Therefore, a technique to block the interaction between the overexpressed sialic acid on cancer cell surfaces and its receptors is a promising approach to develop new cancer therapies. We focused on hydrogels as an artificial barrier to block this interaction and present here the development of a novel technique for selectively covalently binding a thin hydrogel barrier on sialic acid residues on cancer cell surfaces. This technique effectively inhibited cancer cell adhesion, motility and growth, caused cancer cell death in vitro, and completely suppressed tumor growth in vivo, thereby clearly demonstrating a potent antitumor effect.

Eosinophil and mast cell Siglecs: From biology to drug target

Mast cells and eosinophils are innate immune cells involved in both acute and chronic inflammatory responses. Siglecs are a family of cell surface receptors that share sialic acid binding activity. Over the past 20 years, our knowledge of the expression and function of Siglecs on cells of the immune system and others has greatly expanded, as has our understanding of their signaling, ligands, and possible roles in disease pathophysiology. Because of this, Siglecs have garnered interest as potential drug targets using strategies ranging from biologics to ligand-directed nanoparticles. This mini-review will highlight the state of our knowledge regarding human eosinophil and mast cell Siglecs, their biology, what they recognize, tools developed for in vitro and preclinical experimentation, and the status of ongoing efforts to develop drugs that engage eosinophil and mast cell Siglecs for potential therapeutic benefit.

Sialic Acid-Siglec Axis as Molecular Checkpoints Targeting of Immune System: Smart Players in Pathology and Conventional Therapy

The sialic acid-based molecular mimicry in pathogens and malignant cells is a regulatory mechanism that leads to cross-reactivity with host antigens resulting in suppression and tolerance in the immune system. The interplay between sialoglycans and immunoregulatory Siglec receptors promotes foreign antigens hiding and immunosurveillance impairment. Therefore, molecular targeting of immune checkpoints, including sialic acid-Siglec axis, is a promising new field of inflammatory disorders and cancer therapy. However, the conventional drugs used in regular management can interfere with glycome machinery and exert a divergent effect on immune controlling systems. Here, we focus on the known effects of standard therapies on the sialoglycan-Siglec checkpoint and their importance in diagnosis, prediction, and clinical outcomes.

Long noncoding RNA Gm20319, acting as competing endogenous RNA, regulated GNE expression by sponging miR-7240-5p to involve in deoxynivalenol-induced liver damage in vitro

The regulatory effects of competing endogenous RNA (ceRNA) network have been highlighted on the occurrence and development of diseases. However, the effect of ceRNA network in liver with subchronic deoxynivalenol (DON) exposure has remained unclear so far. Here, lncRNA Gm20319-miR-7240-5p-GNE (glucosamine UDP-N-acetyl-2-epimerase/N-acetylmannosamine kinase) network was identified in DON exposed-liver tissues after DON exposure for 90 days. Subchronic DON exposure induced the mild inflammation in liver tissues. In DON-treated liver tissues and Hepa 1-6 cell line, the expression of Gm20319 and GNE were both downregulated while miR-7240-5p expression was upregulated. The gain- and loss-of-function expression in vitro revealed there was a mutual repression between Gm20319 and miR-7240-5p, and they regulated GNE expression in an opposite direction. Dual luciferase reporter assays showed miR-7240-5p inhibited Gm20319 and GNE expression by directly binding. Co-transfection experiment in vitro revealed Gm20319 and miR-7240-5p could indirectly regulate sialic acid level by directly modulating GNE expression, thereby also influencing the expression of SOD1 and IL-1β. This study revealed Gm20319-miR-7240-5p-GNE network reduced sialic acid level to influence the expression of SOD1 and IL-1β in liver, which might involve in liver damage induced by DON. Gm20319 might be a potential research molecular target for DON-induced liver damage.

Treatment of severe sepsis with nanoparticulate cell-free DNA scavengers

Severe sepsis represents a common, expensive, and deadly health care issue with limited therapeutic options. Gaining insights into the inflammatory dysregulation that causes sepsis would help develop new therapeutic strategies against severe sepsis. In this study, we identified the crucial role of cell-free DNA (cfDNA) in the regulation of the Toll-like receptor 9-mediated proinflammatory pathway in severe sepsis progression. Hypothesizing that removing cfDNA would be beneficial for sepsis treatment, we used polyethylenimine (PEI) and synthesized PEI-functionalized, biodegradable mesoporous silica nanoparticles with different charge densities as cfDNA scavengers. These nucleic acid-binding nanoparticles (NABNs) showed superior performance compared with their nucleic acid-binding polymer counterparts on inhibition of cfDNA-induced inflammation and subsequent multiple organ injury caused by severe sepsis. Furthermore, NABNs exhibited enhanced accumulation and retention in the inflamed cecum, along with a more desirable in vivo safety profile. Together, our results revealed a key contribution of cfDNA in severe sepsis and shed a light on the development of NABN-based therapeutics for sepsis therapy, which currently remains intractable.

Cutting Edge: ST8Sia6-Generated α-2,8-Disialic Acids Mitigate Hyperglycemia in Multiple Low-Dose Streptozotocin-Induced Diabetes

The immune system contains a series of checks and balances that maintain tolerance and prevent autoimmunity. Sialic acid-binding Ig-type lectins (Siglecs) are cell surface receptors found on immune cells and inhibit inflammation by recruiting protein tyrosine phosphatases to ITIMs. Islet-resident macrophages express Siglec-E, and Siglec-E expression decreases on islet-resident macrophages as insulitis progresses in the NOD mouse. The sialyltransferase ST8Sia6 generates α-2,8-disialic acids that are ligands for Siglec-E in vivo. We hypothesized that engaging Siglec-E through ST8Sia6-generated ligands may inhibit the development of immune-mediated diabetes. Constitutive overexpression of ST8Sia6 in pancreatic β cells mitigated hyperglycemia in the multiple low-dose streptozotocin model of diabetes, demonstrating that engagement of this immune receptor facilitates tolerance in the setting of inflammation and autoimmune disease.

Choice of Host Cell Line Is Essential for the Functional Glycosylation of the Fc Region of Human IgG1 Inhibitors of Influenza B Viruses

Abs are glycoproteins that carry a conserved N-linked carbohydrate attached to the Fc whose presence and fine structure profoundly impacts on their in vivo immunogenicity, pharmacokinetics, and functional attributes. The host cell line used to produce IgG plays a major role in this glycosylation, as different systems express different glycosylation enzymes and transporters that contribute to the specificity and heterogeneity of the final IgG-Fc glycosylation profile. In this study, we compare two panels of glycan-adapted IgG1-Fc mutants expressed in either the human endothelial kidney 293-F or Chinese hamster ovary-K1 systems. We show that the types of N-linked glycans between matched pairs of Fc mutants vary greatly and in particular, with respect, to sialylation. These cell line effects on glycosylation profoundly influence the ability of the engineered Fcs to interact with either human or pathogen receptors. For example, we describe Fc mutants that potently disrupted influenza B-mediated agglutination of human erythrocytes when expressed in Chinese hamster ovary-K1, but not in human endothelial kidney 293-F cells.

Sialic acid-binding immunoglobulin-like lectins (Siglecs) detect self-associated molecular patterns to regulate immune responses

The mammalian immune system evolved to tightly regulate the elimination of pathogenic microbes and neoplastic transformed cells while tolerating our own healthy cells. Here, we summarize experimental evidence for the role of Siglecs-in particular CD33-related Siglecs-as self-receptors and their sialoglycan ligands in regulating this balance between recognition of self and non-self. Sialoglycans are found in the glycocalyx and extracellular fluids and matrices of all mammalian cells and can be considered as self-associated molecular patterns (SAMPs). We also provide an overview of the known interactions of Siglec receptors and sialoglycan-SAMPs. Manipulation of the Siglec-SAMP axis offers new therapeutic opportunities for the treatment of inflammatory conditions, autoimmune diseases and also cancer immunotherapy.

Elevated levels of lead exposure and impact on the anti-inflammatory ability of oral sialic acids among preschool children in e-waste areas

The oral health of preschool children in an electronic waste (e-waste) area is susceptible to lead (Pb) exposure increasing the risk of dental caries and causing periodontitis and other oral diseases. The aim of the present study is to investigate the relationship between chronic exposure to Pb and oral anti-inflammatory potential of preschool children. For this analysis, 574 preschool children from 2.5 to 6 years of age were recruited between November and December 2017, in which 357 preschool children were from Guiyu (n = 357), an e-waste-contaminated town, and 217 from Haojiang Shantou. We measured the levels of child blood Pb, salivary sialic acid, serum interleukin-6 (IL-6) and serum tumor necrosis factor-α (TNF-α), and investigated the prevalence of dental caries in deciduous teeth. The medians of blood Pb levels, serum IL-6 and TNF-α were significantly higher in the Guiyu children than in Haojiang children. Concomitantly, salivary sialic acids were lower in the Guiyu children [9.58 (3.97, 18.42) mg/dL] than in Haojiang [17.57 (5.95, 24.23) mg/dL]. Additionally, the prevalence of dental caries in deciduous teeth was significantly higher in the Guiyu children than in Haojiang (62.5% vs. 53.9%). Blood Pb levels were negatively correlated with salivary sialic acids, in which IL-6 played as a mediator of the association between blood Pb levels and saliva sialic acid concentrations according to the mediation model. To our knowledge, this is the first report on the potential association between chronic Pb exposure and the anti-inflammatory ability of oral sialic acids among preschool children. These results suggest that the chronic Pb exposure can reduce salivary sialic acid levels, attenuate oral anti-inflammatory potential and increase the potential risk of dental caries in deciduous teeth among preschool children in an e-waste site.

Sialylation and fucosylation modulate inflammasome-activating eIF2 Signaling and microbial translocation during HIV infection

An emerging paradigm suggests that gut glycosylation is a key force in maintaining the homeostatic relationship between the gut and its microbiota. Nevertheless, it is unclear how gut glycosylation contributes to the HIV-associated microbial translocation and inflammation that persist despite viral suppression and contribute to the development of several comorbidities. We examined terminal ileum, right colon, and sigmoid colon biopsies from HIV-infected virally-suppressed individuals and found that gut glycomic patterns are associated with distinct microbial compositions and differential levels of chronic inflammation and HIV persistence. In particular, high levels of the pro-inflammatory hypo-sialylated T-antigen glycans and low levels of the anti-inflammatory fucosylated glycans were associated with higher abundance of glycan-degrading microbial species (in particular, Bacteroides vulgatus), a less diverse microbiome, higher levels of inflammation, and higher levels of ileum-associated HIV DNA. These findings are linked to the activation of the inflammasome-mediating eIF2 signaling pathway. Our study thus provides the first proof-of-concept evidence that a previously unappreciated factor, gut glycosylation, is a force that may impact the vicious cycle between HIV infection, microbial translocation, and chronic inflammation.

Siglecs in Brain Function and Neurological Disorders

Siglecs (Sialic acid-binding immunoglobulin-type lectins) are a I-type lectin that typically binds sialic acid. Siglecs are predominantly expressed in immune cells and generate activating or inhibitory signals. They are also shown to be expressed on the surface of cells in the nervous system and have been shown to play central roles in neuroinflammation. There has been a plethora of reviews outlining the studies pertaining to Siglecs in immune cells. However, this review aims to compile the articles on the role of Siglecs in brain function and neurological disorders. In humans, the most abundant Siglecs are CD33 (Siglec-3), Siglec-4 (myelin-associated glycoprotein/MAG), and Siglec-11, Whereas in mice the most abundant are Siglec-1 (sialoadhesin), Siglec-2 (CD22), Siglec-E, Siglec-F, and Siglec-H. This review is divided into three parts. Firstly, we discuss the general biological aspects of Siglecs that are expressed in nervous tissue. Secondly, we discuss about the role of Siglecs in brain function and molecular mechanism for their function. Finally, we collate the available information on Siglecs and neurological disorders. It is intriguing to study this family of proteins in neurological disorders because they carry immunoinhibitory and immunoactivating motifs that can be vital in neuroinflammation.

A Sulfonamide Sialoside Analogue for Targeting Siglec-8 and -F on Immune Cells

The Siglec family of cell surface receptors have emerged as attractive targets for cell-directed therapies due to their restricted expression on immune cells, endocytic properties, and ability to modulate receptor signaling. Human Siglec-8, for instance, has been identified as a therapeutic target for the treatment of eosinophil and mast cell disorders. A promising strategy to target Siglecs involves the use of liposomal nanoparticles with a multivalent display of Siglec ligands. A key challenge for this approach is the identification of a high affinity ligand for the target Siglec. Here, we report the development of a ligand of Siglec-8 and its closest murine functional orthologue Siglec-F that is capable of targeting liposomes to cells expressing Siglec-8 or -F. A glycan microarray library of synthetic 9-N-sulfonyl sialoside analogues was screened to identify potential lead compounds. The best ligand, 9-N-(2-naphthyl-sulfonyl)-Neu5Acα2-3-[6-O-sulfo]-Galβ1-4GlcNAc (6'-O-sulfo ^NSANeu5Ac) combined the lead 2-naphthyl sulfonyl C-9 substituent with the preferred sulfated scaffold. The ligand 6'-O-sulfo ^NSANeu5Ac was conjugated to lipids for display on liposomes to evaluate targeted delivery to cells. Targeted liposomes showed strong in vitro binding/uptake and selectivity to cells expressing Siglec-8 or -F and, when administered to mice, exhibit in vivo targeting to Siglec-F⁺ eosinophils.

Engineering Cell Membrane-Based Nanotherapeutics to Target Inflammation

Inflammation is ubiquitous in the body, triggering desirable immune response to defend against dangerous signals or instigating undesirable damage to cells and tissues to cause disease. Nanomedicine holds exciting potential in modulating inflammation. In particular, cell membranes derived from cells involved in the inflammatory process may be used to coat nanotherapeutics for effective targeted delivery to inflammatory tissues. Herein, the recent progress of rationally engineering cell membrane-based nanotherapeutics for inflammation therapy is highlighted, and the challenges and opportunities presented in realizing the full potential of cell-membrane coating in targeting and manipulating the inflammatory microenvironment are discussed.

Macrophage-derived nanovesicles exert intrinsic anti-inflammatory properties and prolong survival in sepsis through a direct interaction with macrophages

Despite numerous advances in medical treatment, sepsis remains one of the leading causes of death worldwide. Sepsis is characterized by the involvement of all organs and tissues as a consequence of blood poisoning, resulting in organ failure and eventually death. Effective treatment remains an unmet need and novel approaches are urgently needed. The growing evidence of clinical and biological heterogeneity of sepsis suggests precision medicine as a possible key for achieving therapeutic breakthroughs. In this scenario, biomimetic nanomedicine represents a promising avenue for the treatment of inflammatory diseases, including sepsis. We investigated the role of macrophage-derived biomimetic nanoparticles, namely leukosomes, in a lipopolysaccharide-induced murine model of sepsis. We observed that treatment with leukosomes was associated with significantly prolonged survival. In vitro studies elucidated the potential mechanism of action of these biomimetic vesicles. The direct treatment of endothelial cells (ECs) with leukosomes did not alter the gene expression profile of EC-associated cell adhesion molecules. In contrast, the interaction of leukosomes with macrophages induced a decrease of pro-inflammatory genes (IL-6, IL-1b, and TNF-α), an increase of anti-inflammatory ones (IL-10 and TGF-β), and indirectly an anti-inflammatory response on ECs. Taken together, these results showed the ability of leukosomes to regulate the inflammatory response in target cells, acting as a bioactive nanotherapeutic.

Cargo-less nanoparticles program innate immune cell responses to toll-like receptor activation

Developing biomaterials to control the responsiveness of innate immune cells represents a clinically relevant approach to treat diseases with an underlying inflammatory basis, such as sepsis. Sepsis can involve activation of Toll-like receptor (TLR) signaling, which activates numerous inflammatory pathways. The breadth of this inflammation has limited the efficacy of pharmacological interventions that target a single molecular pathway. Here, we developed cargo-less particles as a single-agent, multi-target platform to elicit broad anti-inflammatory action against innate immune cells challenged by multiple TLR agonists. The particles, prepared from poly(lactic-co-glycolic acid) (PLGA) and poly(lactic acid) (PLA), displayed potent molecular weight-, polymer composition-, and charge-dependent immunomodulatory properties, including downregulation of TLR-induced costimulatory molecule expression and cytokine secretion. Particles prepared using the anionic surfactant poly(ethylene-alt-maleic acid) (PEMA) significantly blunted the responses of antigen presenting cells to TLR4 (lipopolysaccharide) and TLR9 (CpG-ODN) agonists, demonstrating broad inhibitory activity to both extracellular and intracellular TLR ligands. Interestingly, particles prepared using poly(vinyl alcohol) (PVA), a neutrally-charged surfactant, only marginally inhibited inflammatory cytokine secretions. The biochemical pathways modulated by particles were investigated using TRanscriptional Activity CEll aRrays (TRACER), which implicated IRF1, STAT1, and AP-1 in the mechanism of action for PLA-PEMA particles. Using an LPS-induced endotoxemia mouse model, administration of PLA-PEMA particles prior to or following a lethal challenge resulted in significantly improved mean survival. Cargo-less particles affect multiple biological pathways involved in the development of inflammatory responses by innate immune cells and represent a potentially promising therapeutic strategy to treat severe inflammation.

Targeted delivery of ibrutinib to tumor-associated macrophages by sialic acid-stearic acid conjugate modified nanocomplexes for cancer immunotherapy

Ibrutinib (IBR), an irreversible Bruton's tyrosine kinase (BTK) inhibitor, is expected to be a potent therapeutic modality, given that BTK is overexpressed in tumor-associated macrophages (TAMs) and participates in promoting tumor progression, angiogenesis, and immunosuppression. However, rapid clearance in vivo and low tumor accumulation have rendered effective uptake of IBR by TAMs challenge. Herein, we designed and synthesized a sialic acid (SA)-stearic acid conjugate modified on the surface of nanocomplexes to encapsulate IBR (SA/IBR/EPG) for targeted immunotherapy. Amphiphilic egg phosphatidylglycerol (EPG) structure and strong IBR-EPG interactions render these nanocomplexes high IBR loading capacity, prolonged blood circulation, and optimal particle sizes (∼30 nm), which can effectively deliver IBR to the tumor, followed by subsequent internalization of IBR by TAMs through SA-mediated active targeting. In vitro and in vivo tests showed that the prepared SA/IBR/EPG nanocomplexes could preferentially accumulate in TAMs and exert potent antitumor activity. Immunofluorescence staining analysis further confirmed that SA/IBR/EPG remarkably inhibited angiogenesis and tumorigenic cytokines released by TAM and eventually suppressed tumor progression, without eliciting any unwanted effect. Thus, SA-decorated IBR nanocomplexes present a promising strategy for cancer immunotherapy. STATEMENT OF SIGNIFICANCE: Ibrutinib (IBR), an irreversible Bruton's tyrosine kinase (BTK) inhibitor, is expected to be a potent therapeutic modality, given that BTK is overexpressed in tumor-associated macrophages (TAMs) and participates in promoting tumor progression, angiogenesis, and immunosuppression. However, rapid clearance in vivo and low tumor accumulation have rendered effective uptake of IBR by TAMs challenge. Herein, we designed and synthesized a sialic acid (SA)-stearic acid conjugate modified on the surface of nanocomplexes to encapsulate IBR (SA/IBR/EPG) for targeted delivery of IBR to TAMs. The developed SA/IBR/EPG nanocomplexes exhibited high efficiency in targeting TAMs and inhibiting BTK activation, consequently inhibiting Th2 tumorigenic cytokine release, reducing angiogenesis, and suppressing tumor growth. These results implied that the SA/IBR/EPG nanocomplex could be a promising strategy for TAM-targeting immunotherapy with minimal systemic side effects.

Nanoparticles Equipped with α2,8-Linked Sialic Acid Chains Inhibit the Release of Neutrophil Extracellular Traps

Neutrophils can combat the invasion of pathogens by the formation of neutrophil extracellular traps (NETs). The NET mechanism is not only an effective tool for combating pathogens, but is also associated with diseases. Therefore, NETs are a potential target for combating pathologies, such as cystic fibrosis and thrombosis. We investigated the potential of nanoparticles, which were modified with α2,8-linked sialic acid chains, to modulate NET release during phorbol myristate acetate stimulation. Interestingly, when these nanoparticles were applied, the formation of reactive oxygen species was partly inhibited and the release of NET was counteracted. However, although the release of NET fibers was prevented, the nuclei still lost their characteristic segmented structure and became swollen, indicating that only the release, and not complete activation was suppressed. Intriguingly, coincubation of α2,8-sialylated particles with free sialic acid chains prevented the outlined inhibitory effects. Thus, the sialic acid chains must be attached to a linker molecule to generate an active bioconjugate that is able to inhibit the release of NET.

Recent advances in nanomedicine for sepsis treatment

Sepsis and septic shock are life-threating conditions, which form a continuum of the body's response to overwhelming infection. The current treatment consists of fluid and metabolic resuscitation, hemodynamic and end-organ support, and timely initiation of antibiotics. However, these measures may be ineffective and the sepsis-related mortality toll remains substantial; therefore, an urgent need exists for new therapies. Recently, several nanoparticle (NP) systems have shown excellent protective effects against sepsis in preclinical models, suggesting a potential utility in the management of sepsis and septic shock. These NPs serve as antibacterial agents, provide platforms to immobilize endotoxin adsorbents, interact with inflammatory cells to restore homeostasis and detect biomarkers of sepsis for timely diagnosis. This review discusses the recent developments in NP-based approaches for the treatment of sepsis.

Breaking the Glyco-Code of HIV Persistence and Immunopathogenesis

PURPOSE OF REVIEW

Glycoimmunology is an emerging field focused on understanding how immune responses are mediated by glycans (carbohydrates) and their interaction with glycan-binding proteins called lectins. How glycans influence immunological functions is increasingly well understood. In a parallel way, in the HIV field, it is increasingly understood how the host immune system controls HIV persistence and immunopathogenesis. However, what has mostly been overlooked, despite its potential for therapeutic applications, is the role that the host glycosylation machinery plays in modulating the persistence and immunopathogenesis of HIV. Here, we will survey four areas in which the links between glycan-lectin interactions and immunology and between immunology and HIV are well described. For each area, we will describe these links and then delineate the opportunities for the HIV field in investigating potential interactions between glycoimmunology and HIV persistence/immunopathogenesis.

RECENT FINDINGS

Recent studies show that the human glycome (the repertoire of human glycan structures) plays critical roles in driving or modulating several cellular processes and immunological functions that are central to maintaining HIV infection. Understanding the links between glycoimmunology and HIV infection may create a new paradigm for discovering novel glycan-based therapies that can lead to eradication, functional cure, or improved tolerance of lifelong infection.

Modulation of Immune Tolerance via Siglec-Sialic Acid Interactions

One of the key features of the immune system is its extraordinary capacity to discriminate between self and non-self and to respond accordingly. Several molecular interactions allow the induction of acquired immune responses when a foreign antigen is recognized, while others regulate the resolution of inflammation, or the induction of tolerance to self-antigens. Post-translational signatures, such as glycans that are part of proteins (glycoproteins) and lipids (glycolipids) of host cells or pathogens, are increasingly appreciated as key molecules in regulating immunity vs. tolerance. Glycans are sensed by glycan binding receptors expressed on immune cells, such as C-type lectin receptors (CLRs) and Sialic acid binding immunoglobulin type lectins (Siglecs), that respond to specific glycan signatures by triggering tolerogenic or immunogenic signaling pathways. Glycan signatures present on healthy tissue, inflamed and malignant tissue or pathogens provide signals for “self” or “non-self” recognition. In this review we will focus on sialic acids that serve as “self” molecular pattern ligands for Siglecs. We will emphasize on the function of Siglec-expressing mononuclear phagocytes as sensors for sialic acids in tissue homeostasis and describe how the sialic acid-Siglec axis is exploited by tumors and pathogens for the induction of immune tolerance. Furthermore, we highlight how the sialic acid-Siglec axis can be utilized for clinical applications to induce or inhibit immune tolerance.