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Podoplanin (PDPN) is a transmembrane receptor glycoprotein that is upregulated on transformed cells, cancer associated fibroblasts and inflammatory macrophages that contribute to cancer progression. In particular, PDPN increases tumor cell clonal capacity, epithelial mesenchymal transition, migration, invasion, metastasis and inflammation. Antibodies, CAR‐T cells, biologics and synthetic compounds that target PDPN can inhibit cancer progression and septic inflammation in preclinical models. This review describes recent advances in how PDPN may be used as a biomarker and therapeutic target for many types of cancer, including glioma, squamous cell carcinoma, mesothelioma and melanoma. Podoplanin (PDPN) is a transmembrane receptor glycoprotein that is upregulated on transformed cells, cancer associated fibroblasts (CAFs), and inflammatory macrophages that contribute to cancer progression. This review describes recent advances in how PDPN may be used as a biomarker and therapeutic target for many types of cancer including glioma, squamous cell carcinoma, mesothelioma, and melanoma.

Inflammatory pathways and immune system dysregulation participate in the onset and progression of cardiometabolic diseases. The dendritic cell immunoreceptor 2 (DCIR2) is a C-type lectin receptor mainly expressed by conventional type 2 dendritic cells, involved in antigen recognition and in the modulation of T cell response. Here, we investigated the effect of DCIR2 deficiency during the development of obesity. DCIR2 KO mice and the WT counterpart were fed with high-fat diet (HFD) for 20 weeks. Weight gain, glucose and insulin tolerance were assessed, parallel to immune cell subset profiling and histological analysis. After HFD feeding, DCIR2 KO mice presented altered conventional dendritic cell distribution within the liver without affecting markers of hepatic inflammation. These observations were liver restricted, since immune profile of metabolic and lymphoid organs-namely adipose tissue, spleen and mesenteric lymph nodes-did not show differences between the two groups. This reflected in a similar metabolic profile of DCIR2 KO compared to WT mice, characterized by comparable body weight gain as well as adipose tissues, spleen, Peyer's patches and mesenteric lymph nodes weight at sacrifice. Also, insulin response was similar in both groups. Our data show that DCIR2 has a redundant role in the progression of diet-induced obesity and inflammation.

Introduction Cockroach allergen exposure elicits cockroach sensitization and poses an increased risk for asthma. However, the major components in cockroach allergen and the mechanisms underlying the induction of cockroach allergen‐induced allergy and asthma remain largely elusive. We sought to examine the role of cockroach‐associated glycan in regulating human basophil function. Methods N‐linked glycans from naturally purified cockroach allergen Bla g 2 were characterized by MALDI‐TOF mass spectrometry. Binding of cockroach allergen to serum IgE from cockroach allergic subjects was determined by solid‐phase binding immunoassays. Role of cockroach associated glycan in histamine release and IL‐4 production from human basophils was examined. Expression of C‐type lectin receptors (CLRs) and their role in mediating glycan‐uptake in the basophils was also investigated. Results MALDI‐TOF mass spectrometric analysis of N‐glycan from Bla g 2 showed complex hybrid‐types of glycans that terminated with mannose, galactose, and/or N‐acetyl glucosamine (GlcNAc). Deglycosylated Bla g 2 showed reduced binding to IgE and was less capable of inducing histamine release from human basophils. In contrast, N‐glycan derived from Bla g 2 significantly inhibited histamine release and IL‐4 production from basophils passively sensitized with serum from cockroach allergic subjects. An analysis of CLRs revealed the expression of DC‐SIGN and DCIR, but not MRC1 and dectin‐1, in human basophils. Neutralizing antibody to DCIR, but not DC‐SIGN, significantly inhibited Bla g 2 uptake by human basophils. A dose‐dependent bindings of cockroach allergen to DCIR was also observed. Conclusions These observations indicate a previously unrecognized role for cockroach allergen‐associated glycans in allergen‐induced immune reactions, and DCIR may play a role in mediating the regulation of glycan on basophil function. We examined the role of cockroach‐associated glycan in regulating human basophil function. These observations indicate a previously unrecognized role for cockroach associated glycans in allergen‐induced immune reactions, and DCIR may mediate the regulation of glycan on basophil function.

Sensing and reacting to tissue damage is a fundamental function of immune systems. Macrophage inducible C-type lectin (Mincle) is an activating C-type lectin receptor that senses damaged cells. Notably, Mincle also recognizes glycolipid ligands on pathogens. To elucidate endogenous glycolipids ligands derived from damaged cells, we fractionated supernatants from damaged cells and identified a lipophilic component that activates reporter cells expressing Mincle. Mass spectrometry and NMR spectroscopy identified the component structure as β-glucosylceramide (GlcCer), which is a ubiquitous intracellular metabolite. Synthetic β-GlcCer activated myeloid cells and induced production of inflammatory cytokines; this production was abrogated in Mincle-deficient cells. Sterile inflammation induced by excessive cell death in the thymus was exacerbated by hematopoietic-specific deletion of degrading enzyme of β-GlcCer (β-glucosylceramidase, GBA1). However, this enhanced inflammation was ameliorated in a Mincle-deficient background. GBA1-deficient dendritic cells (DCs) in which β-GlcCer accumulates triggered antigen-specific T-cell responses more efficiently than WT DCs, whereas these responses were compromised in DCs from GBA1 × Mincle double-deficient mice. These results suggest that β-GlcCer is an endogenous ligand for Mincle and possesses immunostimulatory activity.

Objectives C‐type lectin receptors (CLRs) are key receptors used by DCs to orchestrate responses to pathogens. During infections, the glycan–lectin interactions shape the virus–host interplay and viruses can subvert the function of CLRs to escape antiviral immunity. Recognition of virus/viral components and uptake by CLRs together with subsequent signalling cascades are crucial in initiating and shaping antiviral immunity, and decisive in the outcome of infection. Yet, the interaction of hepatitis B virus (HBV) with CLRs remains largely unknown. As HBV hijacks DC subsets and viral antigens harbour glycan motifs, we hypothesised that HBV may subvert DCs through CLR binding. Methods We investigated here the pattern of CLR expression on BDCA1+ cDC2s, BDCA2+ pDCs and BDCA3+ cDC1s from both blood and liver of HBV‐infected patients and explored the ability of HBsAg to bind DC subsets through specific CLRs. Results We highlighted for the first time that the CLR repertoire of circulating and intrahepatic cDC2s, cDC1s and pDCs was perturbed in patients with chronic HBV infection and that some CLR expression levels correlated with plasma HBsAg and HBV DNA levels. We also identified candidate CLR responsible for HBsAg binding to cDCs (CD367/DCIR/CLEC4A, CD32/FcɣRIIA) and pDCs (CD369/DECTIN1/CLEC7A, CD336/NKp44) and demonstrated that HBsAg inhibited DC functions in a CLR‐ and glycosylation‐dependent manner. Conclusion HBV may exploit CLR pathways to hijack DC subsets and escape from immune control. Such advances bring insights into the mechanisms by which HBV subverts immunity and pave the way for developing innovative therapeutic strategies to restore an efficient immune control of the infection by manipulating the viral glycan–lectin axis. Dendritic cells (DCs) are crucial in orchestrating immunity to pathogens. Sensing of virus/viral components and uptake by C‐type lectin receptors (CLRs) expressed by DCs initiate and shape antiviral immunity and are decisive in the outcome of infection. We demonstrate that hepatitis B virus exploits CLR pathways to hijack DC subsets and escape from immune control, paving the way for developing innovative antiviral approaches by manipulating the viral glycan–lectin axis.

Glycosylation is an integral post-translational modification present in more than half of all eukaryotic proteins. It affects key protein functions, including folding, stability, and immunogenicity. Glycoengineering approaches, such as the use of bacterial N-glycosylation systems, or expression systems, including yeasts, insect cells, and mammalian cells, have enabled access to defined and homogenous glycoproteins. Given that glycan structures on proteins can be recognized by host lectin receptors, they may facilitate cell-specific targeting and immune modulation. Myeloid C-type lectin receptors (CLRs) expressed by antigen-presenting cells are attractive targets to shape immune responses. Multivalent glycan display on nanoparticles, liposomes, or dendrimers has successfully enabled CLR targeting. In this review, we discuss novel strategies to access defined glycan structures and highlight CLR targeting approaches for immune modulation. Glycosylation affects key protein properties, such as stability, folding, molecular recognition, and immunogenicity. Recent glycoengineering approaches have optimized glycoprotein expression in yeasts, plants, insect cells, and mammalian cells, with the goal of producing glycoproteins with humanized glycosylation in the future. Advances in chemical and chemoenzymatic syntheses will help to obtain glycoproteins with defined and uniform glycosylation patterns. Lectin receptors are attractive targets for carbohydrate-based cell targeting. In particular, CLR targeting is a powerful strategy to shape immune responses. Multivalent glycan display can overcome the low affinities of single lectin–glycan interactions. In this context, glycan presentation on nanoparticles, dendrimers, polymers, and liposomes has proven useful for cell-specific targeting.

The occurrence of the novel severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), responsible for coronavirus disease 2019 (COVD-19), represents a catastrophic threat to global health. Protruding from the viral surface is a densely glycosylated spike (S) protein, which engages angiotensin-converting enzyme 2 (ACE2) to mediate host cell entry. However, studies have reported viral susceptibility in intra- and extrapulmonary immune and non-immune cells lacking ACE2, suggesting that the S protein may exploit additional receptors for infection. Studies have demonstrated interactions between S protein and innate immune system, including C-lectin type receptors (CLR), toll-like receptors (TLR) and neuropilin-1 (NRP1), and the non-immune receptor glucose regulated protein 78 (GRP78). Recognition of carbohydrate moieties clustered on the surface of the S protein may drive receptor-dependent internalization, accentuate severe immunopathological inflammation, and allow for systemic spread of infection, independent of ACE2. Furthermore, targeting TLRs, CLRs, and other receptors (Ezrin and dipeptidyl peptidase-4) that do not directly engage SARS-CoV-2 S protein, but may contribute to augmented anti-viral immunity and viral clearance, may represent therapeutic targets against COVID-19.

Tumor metastasis is the cause of most cancer deaths. Although metastases can form in multiple end organs, the liver is recognized as a highly permissive organ. Nevertheless, there is evidence for immune cell-mediated mechanisms that function to suppress liver metastasis by certain tumors, although the underlying mechanisms for the suppression of metastasis remain elusive. Here, we show that Dectin-2, a C-type lectin receptor (CLR) family of innate receptors, is critical for the suppression of liver metastasis of cancer cells. We provide evidence that Dectin-2 functions in resident macrophages in the liver, known as Kupffer cells, tomediate the uptake and clearance of cancer cells. Interestingly, Kupffer cells are selectively endowed with Dectin-2–dependent phagocytotic activity, with neither bone marrow-derived macrophages nor alveolar macrophages showing this potential. Concordantly, subcutaneous primary tumor growth and lung metastasis are not affected by the absence of Dectin-2. In addition, macrophage C-type lectin, a CLR known to be complex with Dectin-2, also contributes to the suppression of liver metastasis. Collectively, these results highlight the hitherto poorly understood mechanism of Kupffer cell-mediated control of metastasis that is mediated by the CLR innate receptor family, with implications for the development of anticancer therapy targeting CLRs.

C-type lectin receptors (CLRs) are important pattern recognition receptors involved in recognition and induction of adaptive immunity to pathogens. Certain CLRs play an important role in viral infections as they efficiently interact with viruses. However, it has become clear that deadly viruses subvert the function of CLRs to escape antiviral immunity and promote infection. In particular, viruses target CLRs to suppress or modulate type I interferons that play a central role in the innate and adaptive defense against viruses. In this review, we discuss the function of CLRs in binding to enveloped viruses like HIV-1 and Dengue virus, and how uptake and signaling cascades have decisive effects on the outcome of infection.

Cellular lipid uptake (through endocytosis) is a basic physiological process. Dysregulation of this process underlies the pathogenesis of diseases such as atherosclerosis, obesity, diabetes, and cancer. However, to date, only some mechanisms of lipid endocytosis have been discovered. Here, we show a previously unknown mechanism of lipid cargo uptake into cells mediated by the receptor Mincle. We found that the receptor Mincle, previously shown to be a pattern recognition receptor of the innate immune system, tightly binds a range of self-lipids. Moreover, we revealed the minimal molecular motif in lipids that is sufficient for Mincle recognition. Superresolution microscopy showed that Mincle forms vesicles in cytoplasm and colocalizes with added fluorescent lipids in endothelial cells but does not colocalize with either clathrin or caveolin-1, and the added lipids were predominantly incorporated in vesicles that expressed Mincle. Using a model of ganglioside GM3 uptake in brain vessel endothelial cells, we show that the knockout of Mincle led to a dramatic decrease in lipid endocytosis. Taken together, our results have revealed a fundamental lipid endocytosis pathway, which we call Mincle-mediated endocytosis (MiME), and indicate a prospective target for the treatment of disorders of lipid metabolism, which are rapidly increasing in prevalence.