SIGLEC-3 (CD33) serves as an immune checkpoint receptor for HBV infection.

Chronic hepatitis B (CHB) infection is rarely eradicated by current antiviral nucleos(t)ide analogues. We found that α2,6-biantennary sialoglycans of HBV surface antigen (HBsAg) bound human SIGLEC-3 (CD33) by IP and ELISA, and the binding affinity between SIGLEC-3 and α2,6-biantennary sialoglycans was determined by biolayer interferometry (equilibrium dissociation constant [KD]: 1.95 × 10-10 ± 0.21 × 10-10 M). Moreover, HBV activated SIGLEC-3 on myeloid cells and induced immunosuppression by stimulating immunoreceptor tyrosine-based inhibitory motif phosphorylation and SHP-1/-2 recruitment via α2,6-biantennary sialoglycans on HBsAg. An antagonistic anti-SIGLEC-3 mAb reversed this effect and enhanced cytokine production in response to TLR-7 agonist GS-9620 in PBMCs from CHB patients. Moreover, anti-SIGLEC-3 mAb alone was able to upregulate the expression of molecules involved in antigen presentation, such as CD80, CD86, CD40, MHC-I, MHC-II, and PD-L1 in CD14+ cells. Furthermore, SIGLEC-3 SNP rs12459419 C, which expressed a higher amount of SIGLEC-3, was associated with increased risk of hepatocellular carcinoma (HCC) in CHB patients (HR: 1.256, 95% CI: 1.027-1.535, P = 0.0266). Thus, blockade of SIGLEC-3 is a promising strategy to reactivate host immunity to HBV and lower the incidence of HCC in the CHB patient population.

Decoy Receptor 3 Inhibits Monosodium Urate-Induced NLRP3 Inflammasome Activation via Reduction of Reactive Oxygen Species Production and Lysosomal Rupture.

Gout is a common inflammatory arthritis caused by the deposition of monosodium urate (MSU) crystals in the joints. This activates the macrophages into a proinflammatory state by inducing NLRP3-dependent interleukin-1ß (IL-1ß) secretion, resulting in neutrophil recruitment. Soluble decoy receptor 3 (DcR3) is an immune modulator and can exert biological functions via decoy and non-decoy actions. Previously, we showed that DcR3 suppresses lipopolysaccharides (LPS)- and virus-induced inflammatory responses in the macrophages and promotes the macrophages into the M2 phenotype. In this study, we clarified the actions of DcR3 and its non-decoy action motif heparin sulfate proteoglycan (HSPG) binding domain (HBD) in the MSU crystal-induced NLRP3 inflammasome activation in the macrophages and in mice. In bone marrow-derived macrophages, THP-1 and U937 cells, we found that the MSU crystal-induced secretion of IL-1ß and activation of NLRP3 were suppressed by both DcR3.Fc and HBD.Fc. The suppression of the MSU-induced NLRP3 inflammasome activation is accompanied by the inhibition of lysosomal rupture, mitochondrial production of the reactive oxygen species (ROS), expression of cathepsins, and activity of cathepsin B, without affecting the crystal uptake and the expression of NLRP3 or pro-IL-1ß. In the air pouch mice model of gout, MSU induced less amounts of IL-1ß and chemokines secretion, an increased M2/M1 macrophage ratio, and a reduction of neutrophil recruitment in DcR3-transgenic mice, which expresses DcR3 in myeloid cells. Similarly, the mice intravenously treated with DcR3.Fc or HBD.Fc displayed less inflammation response. These findings indicate that HBD of DcR3 can reduce MSU crystal-induced NLRP3 inflammasome activation via modulation of mitochondrial and lysosomal functions. Therefore, we, for the first time, demonstrate a new therapeutic potential of DcR3 for the treatment of gout.

Endosomal TLR3 co-receptor CLEC18A enhances host immune response to viral infection.

Human C-type lectin member 18A (CLEC18A) is ubiquitously expressed in human, and highest expression levels are found in human myeloid cells and liver. In contrast, mouse CLEC18A (mCLEC18A) is only expressed in brain, kidney and heart. However, the biological functions of CLEC18A are still unclear. We have shown that a single amino acid change (S339 →R339) in CTLD domain has profound effect in their binding to polysaccharides and house dust mite allergens. In this study, we further demonstrate that CLEC18A and its mutant CLEC18A(S339R) associate with TLR3 in endosome and bind poly (I:C) specifically. Compared to TLR3 alone, binding affinity to poly (I:C) is further increased in TLR3-CLEC18A and TLR3-CLEC18A(S339R) complexes. Moreover, CLEC18A and CLEC18A(S339R) enhance the production of type I and type III interferons (IFNs), but not proinflammatory cytokines, in response to poly (I:C) or H5N1 influenza A virus (IAV) infection. Compared to wild type (WT) mice, ROSA-CLEC18A and ROSA-CLEC18A(S339R) mice generate higher amounts of interferons and are more resistant to H5N1 IAV infection. Thus, CLEC18A is a TLR3 co-receptor, and may contribute to the differential immune responses to poly (I:C) and IAV infection between human and mouse.

Antibody blockade of Dectin-2 suppresses house dust mite-induced Th2 cytokine production in dendritic cell- and monocyte-depleted peripheral blood mononuclear cell co-cultures from asthma patients.

BACKGROUND: Dectin-2, which is a C-type lectin, interacts with the house dust mite (HDM) Dermatophagoides pteronyssinus allergen. This study aimed to investigate whether Dectin-2 blockade by antagonistic monoclonal antibodies (MoAbs) attenuates HDM-induced allergic responses. METHODS: Two anti-Dectin-2 MoAbs were generated and validated for specific binding to Dectin-2 Fc fusion protein (Dectin-2.Fc) and inhibition of Dectin-2.Fc/HDM interaction. Patients with asthma exhibiting high titers of anti-D. pteronyssinus IgE were enrolled. Peripheral blood mononuclear cells with depleted CD14+ monocytes were obtained from these patients and co-cultured with autologous monocyte-derived conventional dendritic cells in the presence of D. pteronyssinus or its group 2 allergens (Der p 2). Interleukin (IL)-5 and IL-13 levels in the culture supernatants were determined using ELISA in the presence or absence of anti-Dectin-2 MoAbs. RESULTS: Two MoAbs, 6A4G7 and 17A1D10, showed specific binding to recombinant Dectin-2.Fc and inhibited HDM binding to Dectin-2.Fc. Both anti-Dectin-2 MoAbs inhibited IL-5 and IL-13 production in co-cultures with Der p 2 stimulation in a dose-dependent manner. 6A4G7 and 17A1D10 (3 µg/mL) significantly inhibited Der p 2-induced (3 µg/mL) IL-5 production by 69.7 and 86.4% and IL-13 production by 84.0 and 81.4%, respectively. Moreover, this inhibitory effect of the two MoAbs remained significant in the presence of D. pteronyssinus. CONCLUSIONS: Anti-Dectin-2 MoAbs significantly inhibited HDM-induced allergic responses in vitro and therefore have the potential to become therapeutic agents in mite-induced allergic diseases.

Decoy receptor 3 promotes cell adhesion and enhances endometriosis development.

Endometriosis is a multifactorial inflammatory disease with persistent activation of the nuclear factor-κB (NF-κB) signalling pathway. Aberrant adhesion of endometrium is the essential step in the progression of endometriosis, but the molecular mechanism of ectopic growth of endometrium is still unclear. Decoy receptor 3 (DcR3)/TNFRSF6B, a pleiotropic immunomodulator regulated by oestrogen, is able to activate focal adhesion kinase to promote cell adhesion. We found that DcR3 is upregulated in human ectopic endometrial cells via activation of the Akt-NF-κB signalling pathway, and its expression level correlates positively with that of the adhesion molecules intercellular adhesion molecule 1 (ICAM-1) and homing cell adhesion molecule (HCAM; CD44). In a multivariate regression model, DcR3 expression level was the most significant parameter associated with endometriosis severity. Knockdown of DcR3 not only downregulated the expression of ICAM-1 and HCAM, but also reduced cell adhesion and migration. In vivo investigation further showed that DcR3 promoted the growth and spread of endometrium, whereas knockdown of DcR3 by lentivirus-delivered short hairpin RNA inhibited ectopic adhesion of endometrium and abrogated endometriosis progression. These observations are in support of DcR3 playing a critical role in the pathogenesis of endometriosis, and the inhibition of DcR3 expression being a promising approach for the treatment of endometriosis. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

DcR3 suppresses influenza virus-induced macrophage activation and attenuates pulmonary inflammation and lethality.

UNLABELLED: Influenza A virus (IAV) infects macrophages and stimulates innate immunity receptors and sensors to produce proinflammatory cytokines and chemokines, which are responsible for IAV-induced pulmonary inflammation and injury. Decoy receptor 3 (DcR3) is a soluble protein belonging to the tumor necrosis factor receptor superfamily (TNFRSF), and is able to skew macrophage differentiation into an M2 phenotype. We demonstrated that DcR3 attenuated IAV-induced secretion of proinflammatory cytokines and chemokine from macrophages, and mitigated pulmonary infiltration and reduce lethality. Proteome-wide phosphoproteomic mapping revealed that DcR3 not only activated STK10, a negative regulator of cell migration, but also inactivated PKC-α, which are crucial for the activation of ERK and JNK in human macrophages. Furthermore, less pulmonary infiltration with lower levels of proinflammatory cytokines and chemokine in bronchoalveolar lavage fluid (BALF) were observed in DcR3-transgenic mice. Moreover, recombinant DcR3.Fc and heparan sulfate proteoglycan binding domain of DcR3.Fc (HBD.Fc) fusion proteins attenuated weight loss and protected mice from IAV-induced lethality. Thus, DcR3-mediated protection is not only via suppression of proinflammatory cytokine and chemokine release, but also via activation of STK10 to inhibit cell infiltration. DcR3 fusion proteins may become therapeutic agents to protect host from IAV-induced lethality in the future. KEY MESSAGE: • DcR3 suppresses IAV-induced cytokine secretion.• DcR3 inhibits IAV-induced JNK and ERK activation in human macrophages.• DcR3 downregulates TLR3 and 7 expressions in human macrophages.• DcR3 protects mice from IAV-induced lethality.

Profiling carbohydrate-receptor interaction with recombinant innate immunity receptor-Fc fusion proteins.

The recognition of bacteria, viruses, fungi, and other microbes is controlled by host immune cells, which are equipped with many innate immunity receptors, such as Toll-like receptors, C-type lectin receptors, and immunoglobulin-like receptors. Our studies indicate that the immune modulating properties of many herbal drugs, for instance, the medicinal fungus Reishi (Ganoderma lucidum) and Cordyceps sinensis, could be attributed to their polysaccharide components. These polysaccharides specifically interact with and activate surface receptors involved in innate immunity. However, due to the complexity of polysaccharides and their various sources from medicinal fungi, quantitative analysis of medicinal polysaccharide extracts with regard to their functions represents a major challenge. To profile carbohydrate-immune receptor interactions, the extracellular domains of 17 receptors were cloned as Fc-fusion proteins, such that their interactions with immobilized polysaccharides could be probed in an enzyme-linked immunosorbent assay. The results show that several innate immune receptors, including Dectin-1, DC-SIGN, Langerin, Kupffer cell receptor, macrophage mannose receptor, TLR2, and TLR4, interact with the polysaccharide extracts from G. lucidum (GLPS). This analysis revealed distinct polysaccharide profiles from different sources of medicinal fungi, and the innate immune receptor-based enzyme-linked immunosorbent assay described here can serve as a high-throughput profiling method for the characterization and quality control of medicinal polysaccharides. It also provides a means to dissect the molecular mechanism of medicinal polysaccharide-induced immunomodulation events.

CLEC5A is critical for dengue-virus-induced lethal disease.

Dengue haemorrhagic fever and dengue shock syndrome, the most severe responses to dengue virus (DV) infection, are characterized by plasma leakage (due to increased vascular permeability) and low platelet counts. CLEC5A (C-type lectin domain family 5, member A; also known as myeloid DAP12-associating lectin (MDL-1)) contains a C-type lectin-like fold similar to the natural-killer T-cell C-type lectin domains and associates with a 12-kDa DNAX-activating protein (DAP12) on myeloid cells. Here we show that CLEC5A interacts with the dengue virion directly and thereby brings about DAP12 phosphorylation. The CLEC5A-DV interaction does not result in viral entry but stimulates the release of proinflammatory cytokines. Blockade of CLEC5A-DV interaction suppresses the secretion of proinflammatory cytokines without affecting the release of interferon-alpha, supporting the notion that CLEC5A acts as a signalling receptor for proinflammatory cytokine release. Moreover, anti-CLEC5A monoclonal antibodies inhibit DV-induced plasma leakage, as well as subcutaneous and vital-organ haemorrhaging, and reduce the mortality of DV infection by about 50% in STAT1-deficient mice. Our observation that blockade of CLEC5A-mediated signalling attenuates the production of proinflammatory cytokines by macrophages infected with DV (either alone or complexed with an enhancing antibody) offers a promising strategy for alleviating tissue damage and increasing the survival of patients suffering from dengue haemorrhagic fever and dengue shock syndrome, and possibly even other virus-induced inflammatory diseases.