C-type lectins in immunity: recent developments

Syk-dependent glycolytic reprogramming in dendritic cells regulates IL-1β production to β-glucan ligands in a TLR-independent manner

Dendritic cells (DCs) activated via TLR ligation experience metabolic reprogramming, in which the cells are heavily dependent on glucose and glycolysis for the synthesis of molecular building blocks essential for maturation, cytokine production, and the ability to stimulate T cells. Although the TLR-driven metabolic reprogramming events are well documented, fungal-mediated metabolic regulation via C-type lectin receptors such as Dectin-1 and Dectin-2 is not clearly understood. Here, we show that activation of DCs with fungal-associated β-glucan ligands induces acute glycolytic reprogramming that supports the production of IL-1β and its secretion subsequent to NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome activation. This acute glycolytic induction in response to β-glucan ligands requires spleen tyrosine kinase signaling in a TLR-independent manner, suggesting now that different classes of innate immune receptors functionally induce conserved metabolic responses to support immune cell activation. These studies provide new insight into the complexities of metabolic regulation of DCs immune effector function regarding cellular activation associated with protection against fungal microbes.

Glutathione Reductase Promotes Fungal Clearance and Suppresses Inflammation during Systemic Candida albicans Infection in Mice

Glutathione reductase (Gsr) catalyzes the reduction of glutathione disulfide to glutathione, which plays an important role in redox regulation. We have previously shown that Gsr facilitates neutrophil bactericidal activities and is pivotal for host defense against bacterial pathogens. However, it is unclear whether Gsr is required for immune defense against fungal pathogens. It is also unclear whether Gsr plays a role in immunological functions outside of neutrophils during immune defense. In this study, we report that Gsr^-/- mice exhibited markedly increased susceptibility to Candida albicans challenge. Upon C. albicans infection, Gsr^-/- mice exhibited dramatically increased fungal burden in the kidneys, cytokine and chemokine storm, striking neutrophil infiltration, histological abnormalities in both the kidneys and heart, and substantially elevated mortality. Large fungal foci surrounded by massive numbers of neutrophils were detected outside of the glomeruli in the kidneys of Gsr ^-/- mice but were not found in wild-type mice. Examination of the neutrophils and macrophages of Gsr^-/- mice revealed several defects. Gsr ^-/- neutrophils exhibited compromised phagocytosis, attenuated respiratory burst, and impaired fungicidal activity in vitro. Moreover, upon C. albicans stimulation, Gsr ^-/- macrophages produced increased levels of inflammatory cytokines and exhibited elevated p38 and JNK activities, at least in part, because of lower MAPK phosphatase (Mkp)-1 activity and greater Syk activity. Thus, Gsr-mediated redox regulation is crucial for fungal clearance by neutrophils and the proper control of the inflammatory response by macrophages during host defense against fungal challenge.

Innate immunity in allergy

Innate immune system quickly responds to invasion of microbes and foreign substances through the extracellular and intracellular sensing receptors, which recognize distinctive molecular and structural patterns. The recognition of innate immune receptors leads to the induction of inflammatory and adaptive immune responses by activating downstream signaling pathways. Allergy is an immune-related disease and results from a hypersensitive immune response to harmless substances in the environment. However, less is known about the activation of innate immunity during exposure to allergens. New insights into the innate immune system by sensors and their signaling cascades provide us with more important clues and a framework for understanding allergy disorders. In this review, we will focus on recent advances in the innate immune sensing system.

A single-CRD C-type lectin (CgCLec-3) with novel DIN motif exhibits versatile immune functions in Crassostrea gigas

C-type lectins (CTLs), as important pattern recognition receptors (PRRs), are a superfamily of Ca²⁺-dependent carbohydrate-recognition proteins which participate in nonself-recognition and eliminating pathogens. In the present study, a novel CTL (designated as CgCLec-3) was identified from the Pacific oyster Crassostrea gigas. There was only one carbohydrate-recognition domain (CRD) of 151 amino acid residues within the deduced amino acid sequence of CgCLec-3. The deduced amino acid sequence of CgCLec-3 CRD shared low homology with the CRDs of other CTLs in oyster with the identities ranging from 12% to 22%. A novel DIN motif was found in Ca²⁺-binding site 2 of CgCLec-3. The relative expression level of CgCLec-3 in hemocytes was up-regulated significantly after the stimulations of bacteria and Pathogen Associated Molecular Patterns (PAMPs). Immunohistochemistry assay showed that CgCLec-3 protein was mainly distributed in gill and mantle, less in gonad, and could not be detected in adductor muscle and hepatopancreas. The recombinant protein (rCgCLec-3) could bind lipopolysaccharide (LPS), mannose (MAN) and peptidoglycan (PGN), but not poly (I:C). rCgCLec-3 exihibited strong binding ability to Vibrio anguillarum and V. splendidus, moderate binding activities to Escherichia coli, Pichia pastoris and Yarrowia lipolytica, weak binding affinity to Staphylococcus aureus and Micrococcus luteus. rCgCLec-3 could agglutinate microorganisms, in a Ca²⁺-dependent manner and its activity to agglutinate V. splendidus was remarkably higher than that to agglutinate E. coli, S. aureus and P. pastoris. The phagocytic activity of oyster hemocytes was significantly enhanced after incubation with rCgCLec-3. rCgCLec-3 also exhibited antibacterial activity against E. coli and S. aureus. The results clearly suggested that CgCLec-3 in Pacific oyster C. gigas not only served as a PRR involved in the PAMPs recognition and microbes binding, but also functioned as an immune effector participating in the clearance of invaders.

A novel C-type lectin from spotted knifejaw, Oplegnathus punctatus possesses antibacterial and anti-inflammatory activity

C-type lectin is a type of carbohydrate-binding protein and plays significant roles in innate immune response against pathogen infection. To date, thousands of C-type lectin had been identified in teleost. In the present study, we isolated a novel isoform of C-type lectin (OppCTL) from spotted knifejaw (Oplegnathus punctatus). The OppCTL encoded a typical Ca²⁺-dependent carbohydrate-binding protein, and was mainly expressed in liver in a tissue specific fashion. The expression of OppCTL was significantly up-regulated following Vibrio anguillarum infection in vivo, suggesting involvement in immune response. Hemagglutination analysis showed that the recombinant OppCTL (rOppCTL) could agglutinate erythrocyte from Mus musculus, Oplegnathus punctatus, Sebastes schlegelii and Paralichthys olivaceus. The rOppCTL could bind and agglutinate all tested bacteria. The rOppCTL possessed capacities of calcium-dependent agglutination to all tested bacteria. Sugar binding assay revealed that rOppCTL could also bind to the glycoconjugates of the bacterial surface, including lipopolysaccharide and peptidoglycan. Interestingly, Dual-luciferase analysis revealed that OppCTL could inhibit the activity of NF-κB in HEK-293T cells after OppCTL overexpression. Taken together, these results indicate that OppCTL has immune activity capable of defending invading pathogens and possesses potential immunoregulatory activity, enriching our understanding of the function of C-type lectin.

The uric acid crystal receptor Clec12A potentiates type I interferon responses

Viral infections are accompanied by the release of pathogen-associated molecular patterns (PAMPs) during the virus life-cycle and damage-associated molecular patterns (DAMPs) from collateral injured cells. The sensing of viral PAMPs by pattern recognition receptors (PRRs) such as Toll-like receptors RIG-I and cGAS is essential in initiating host antiviral responses, especially the type I interferon (IFN-I) response. Here, we report that the DAMP-sensing C-type lectin receptor Clec12A positively regulates the IFN-I response induced by RIG-I, providing a mechanism of cross-talk between PAMP- and DAMP-triggered signaling pathways. Moreover, this modulatory function of Clec12A has functional consequences in both acute and chronic viral infection in mice.

The detection of microbes and damaged host cells by the innate immune system is essential for host defense against infection and tissue homeostasis. However, how distinct positive and negative regulatory signals from immune receptors are integrated to tailor specific responses in complex scenarios remains largely undefined. Clec12A is a myeloid cell-expressed inhibitory C-type lectin receptor that can sense cell death under sterile conditions. Clec12A detects uric acid crystals and limits proinflammatory pathways by counteracting the cell-activating spleen tyrosine kinase (Syk). Here, we surprisingly find that Clec12A additionally amplifies type I IFN (IFN-I) responses in vivo and in vitro. Using retinoic acid-inducible gene I (RIG-I) signaling as a model, we demonstrate that monosodium urate (MSU) crystal sensing by Clec12A enhances cytosolic RNA-induced IFN-I production and the subsequent induction of IFN-I–stimulated genes. Mechanistically, Clec12A engages Src kinase to positively regulate the TBK1-IRF3 signaling module. Consistently, Clec12A-deficient mice exhibit reduced IFN-I responses upon lymphocytic choriomeningitis virus (LCMV) infection, which affects the outcomes of these animals in acute and chronic virus infection models. Thus, our results uncover a previously unrecognized connection between an MSU crystal-sensing receptor and the IFN-I response, and they illustrate how the sensing of extracellular damage-associated molecular patterns (DAMPs) can shape the immune response.

C-type lectins in immunity and homeostasis

The C-type lectins are a superfamily of proteins that recognize a broad repertoire of ligands and that regulate a diverse range of physiological functions. Most research attention has focused on the ability of C-type lectins to function in innate and adaptive antimicrobial immune responses, but these proteins are increasingly being recognized to have a major role in autoimmune diseases and to contribute to many other aspects of multicellular existence. Defects in these molecules lead to developmental and physiological abnormalities, as well as altered susceptibility to infectious and non-infectious diseases. In this Review, we present an overview of the roles of C-type lectins in immunity and homeostasis, with an emphasis on the most exciting recent discoveries.

Human thioredoxin, a damage-associated molecular pattern and Malassezia-crossreactive autoallergen, modulates immune responses via the C-type lectin receptors Dectin-1 and Dectin-2

Human thioredoxin (hTrx), which can be secreted from cells upon stress, functions in allergic skin inflammation as a T cell antigen due to homology and cross-reactivity with the fungal allergen Mala s13 of the skin-colonizing yeast Malassezia sympodialis. Recent studies have shown that cell wall polysaccharides of Malassezia are detected by the immune system via the C-type lectin receptors Dectin-1 and Dectin-2, which are expressed on myeloid cells. Therefore, this study aimed to investigate a putative interaction between Dectin-1, Dectin-2 and the allergens Mala s13 and hTrx. Stimulation of human monocyte-derived dendritic cells or macrophages with Mala s13 or hTrx resulted in remarkable secretion of IL-1β and IL-23. Blocking experiments suggest that hTrx induces IL-23 by Dectin-1 binding and IL-1β by binding to either Dectin-1 or Dectin-2. Regarding Mala s13, Dectin-1 appears to be involved in IL-1β signaling. Interference of Syk kinase function was performed to investigate downstream signaling, which led to diminished hTrx responses. In our experiments, we observed rapid internalization of Mala s13 and hTrx upon cell contact and we were able to confirm direct interaction with Dectin-1 as well as Dectin-2 applying a fusion protein screening platform. We hypothesize that this cytokine response may result in a Th2/Th17-polarizing milieu, which may play a key role during the allergic sensitization in the skin, where allergen presentation to T cells is accompanied by microbial colonization and skin inflammation.

The macrophage tetraspan MS4A4A enhances dectin-1-dependent NK cell-mediated resistance to metastasis

The plasma membrane tetraspan molecule MS4A4A is selectively expressed by macrophage-lineage cells, but its function is unknown. Here we report that MS4A4A was restricted to murine and human mononuclear phagocytes and was induced during monocyte-to-macrophage differentiation in the presence of interleukin 4 or dexamethasone. Human MS4A4A was co-expressed with M2/M2-like molecules in subsets of normal tissue-resident macrophages, infiltrating macrophages from inflamed synovium and tumor-associated macrophages. MS4A4A interacted and colocalized with the β-glucan receptor dectin-1 in lipid rafts. In response to dectin-1 ligands, Ms4a4a-deficient macrophages showed defective signaling and defective production of effector molecules. In experimental models of tumor progression and metastasis, Ms4a4a deficiency in macrophages had no impact on primary tumor growth, but was essential for dectin-1-mediated activation of macrophages and natural killer (NK) cell-mediated metastasis control. Thus, MS4A4A is a tetraspan molecule selectively expressed in macrophages during differentiation and polarization, essential for dectin-1-dependent activation of NK cell-mediated resistance to metastasis.

Morphometric image analysis of placental C-type lectin domain family 2, member D (CLEC2D) immuno-expression in HIV associated pre-eclampsia

OBJECTIVE

C-type lectin domain family 2, member D (CLEC2D) is implicated in the immune response. Pre-eclampsia and HIV infection have opposing immune responses. In view of the high prevalence of HIV infection and pre-eclampsia in South Africa, this study assessed the placental immuno-expression of CLEC2D in HIV associated pre-eclampsia.

METHOD

Placental tissue was obtained from 60 pregnancies which were categorized according to pregnancy type (pre-eclamptic or normotensive) and HIV status (positive or negative). Immunohistochemistry and morphometric image analysis were used to evaluate placental CLEC2D immuno-expression.

RESULTS

CLEC2D expression was significantly decreased in the conducting villi of pre-eclamptic vs normotensive placentae (p = 0.0418) but was increased in the exchange villi, albeit non-significant (p = 0.4948). HIV positive status intensified placental CLEC2D immuno-expression in conducting (p = 0.0312) and exchange (p = 0.0025) villi. CLEC2D expression was significantly different in exchange vs conducting villi (p < 0.0001) and across study groups (p = 0.0003). Normotensive; HIV negative placentae (control) had a non-significant difference in CLEC2D expression across villi types, however significant difference was noted within the remaining groups: normotensive; HIV positive (p < 0.05), pre-eclamptic; HIV positive (p < 0.01 and pre-eclamptic; HIV negative (p < 0.001).

CONCLUSION

The contrasting expression of CLEC2D in HIV infection and pre-eclampsia is demonstrative of the immunosuppressive and pro-inflammatory roles of the respective pathologies. However, this implication may be confounded by highly active anti-retroviral treatment (HAART).

Proteomic Investigation of a Diseased Gorgonian Coral Indicates Disruption of Essential Cell Function and Investment in Inflammatory and Other Immune Processes

As scleractinian coral cover declines in the face of increased frequency in disease outbreaks, future reefs may become dominated by octocorals. Understanding octocoral disease responses and consequences is therefore necessary if we are to gain insight into the future of ecosystem services provided by coral reefs. In Florida, populations of the octocoral Eunicea calyculata infected with Eunicea black disease (EBD) were observed in the field in the fall of 2011. This disease was recognized by a stark, black pigmentation caused by heavy melanization. Histological preparations of E. calyculata infected with EBD demonstrated granular amoebocyte (GA) mobilization, melanin granules in much of the GA population, and the presence of fungal hyphae penetrating coral tissue. Previous transcriptomic analysis also identified immune trade-offs evidenced by increased immune investment at the expense of growth. Our investigation utilized proteogenomic techniques to reveal decreased investment in general cell signaling while increasing energy production for immune responses. Inflammation was also prominent in diseased E. calyculata and sheds light on factors driving the extreme phenotype observed with EBD. With disease outbreaks continuing to increase in frequency, our results highlight new targets within the cnidarian immune system and provide a framework for understanding transcriptomics in the context of an organismal disease phenotype and its protein expression.

Total Synthesis of an Immunogenic Trehalose Phospholipid from Salmonella Typhi and Elucidation of Its sn-Regiochemistry by Mass Spectrometry

Diphosphatidyltrehalose (diPT) is an immunogenic glycolipid, recently isolated from Salmonella Typhi. Despite rigorous structure elucidation, the sn-position of the acyl chains on the glycerol backbone had not been unequivocally established. A stereoselective synthesis of diPT and its regioisomer is reported herein. Using a hybrid MS³ approach combining collisional dissociation and ultraviolet photodissociation mass spectrometry for analysis of the regioisomers and natural diPT, the regiochemistry of the acyl chains of this abundant immunostimulatory glycolipid was established.

Immune Function and Diversity of Osteoclasts in Normal and Pathological Conditions

Osteoclasts (OCLs) are key players in controlling bone remodeling. Modifications in their differentiation or bone resorbing activity are associated with a number of pathologies ranging from osteopetrosis to osteoporosis, chronic inflammation and cancer, that are all characterized by immunological alterations. Therefore, the 2000s were marked by the emergence of osteoimmunology and by a growing number of studies focused on the control of OCL differentiation and function by the immune system. At the same time, it was discovered that OCLs are much more than bone resorbing cells. As monocytic lineage-derived cells, they belong to a family of cells that displays a wide heterogeneity and plasticity and that is involved in phagocytosis and innate immune responses. However, while OCLs have been extensively studied for their bone resorption capacity, their implication as immune cells was neglected for a long time. In recent years, new evidence pointed out that OCLs play important roles in the modulation of immune responses toward immune suppression or inflammation. They unlocked their capacity to modulate T cell activation, to efficiently process and present antigens as well as their ability to activate T cell responses in an antigen-dependent manner. Moreover, similar to other monocytic lineage cells such as macrophages, monocytes and dendritic cells, OCLs display a phenotypic and functional plasticity participating to their anti-inflammatory or pro-inflammatory effect depending on their cell origin and environment. This review will address this novel vision of the OCL, not only as a phagocyte specialized in bone resorption, but also as innate immune cell participating in the control of immune responses.

Development and characterization of a stable bovine intestinal sub-epithelial myofibroblast cell line from ileum of a young calf

Intestinal sub-epithelial myofibroblasts (ISEMFs) are mesenchymal cells that do not express cytokeratin but express α-smooth muscle actin and vimentin. Despite being cells with diverse functions, there is a paucity of knowledge about their origin and functions primarily due to the absence of a stable cell line. Although myofibroblast in vitro models for human, mouse, and pig are available, there is no ISEMF cell line available from young calves. We isolated and developed an ileal ISEMF cell line from a 2-d-old calf that expressed α-smooth muscle actin and vimentin but no cytokeratin indicating true myofibroblast cells. To overcome replicative senescence, we immortalized primary cells with SV40 large T antigen. We characterized and compared both primary and immortalized ileal ISEMF cells for surface glycan and Toll-like-receptor (TLR) expression by lectin-binding assay and real-time quantitative PCR (RT-qPCR) assay respectively. SV40 immortalization significantly decreased surface lectin binding for lectins GSL-I, PHA-L, ECL, Jacalin, Con-A, LCA, and LEL. Both cell types expressed TLRs 1-9 and showed no significant differences in TLR expression. Thus, these cells can be useful in vitro model to study ISEMF's origin, physiology, and functions.

The lectin domain containing proteins with mucosal immunity and digestive functions in oyster Crassostrea gigas

Lectins are carbohydrate-binding proteins with lectin domains, which are extensively studied for their numerous roles in biological recognition. However, the lectin domain containing proteins (LDCPs) chimerized with other non-lectin domains have not received sufficient attention. In the present study, a genome-wide survey of LDCPs in oyster Crassostrea gigas was conducted, and an expansive 640 LDCPs derived from ten lectin domains were identified and functionally explored. In these LDCPs, a total of 282 kinds of domains were predicted, and 90% of the LDCPs contained more than one kind of domain. The lectin domains were frequently fused with non-lectin domains, such as epidermal growth factor domain and peptidase related domains, which supplied LDCPs with more diversity in structures and functions. The C-type lectin domains were the most abundant domains in LDCPs, and they were largely co-existed with non-lectin domains of complement activation-related domains (such as CUB domain and PAN-1 domain) but relative independence with other lectin domains. Furthermore, the C-type lectin domain containing proteins (CTLPs) found to mainly act as pattern immune recognition receptors and were highly expressed in mucosal tissues (digestive gland, male gonad and labial palp) to provide mucosal immune protections. The Concanavalin A-like lectin domains were the second richest domains in LDCPs, and they were mostly constructed into chimeric proteins with epidermal growth factor domain and peptidase related domains. The Concanavalin A-like lectin domain containing proteins (CALPs) were significantly enriched with peptidase activities and mainly expressed in digestive tissues. All the results suggested the mucosal immunity and digestive functions of oyster LDCPs, which provided a fresh idea about the functions of invertebrate lectin family.

The Cross-Talk between miR-511-3p and C-Type Lectin Receptors on Dendritic Cells Affects Dendritic Cell Function

MicroRNAs are small, noncoding RNAs that function as posttranscriptional modulators of gene expression by binding target mRNAs and inhibiting translation. They are therefore crucial regulators of several biological as well as immunological events. Recently, miR-511-3p has been implicated in the development and differentiation of APCs, such as dendritic cells (DCs), and regulating several human diseases. Interestingly, miR-511-3p is embedded within the human MRC1 gene that encodes the mannose receptor. In this study, we sought to examine the impact of miR-511-3p up- or downregulation on human DC surface phenotype, cytokine profile, immunogenicity (using IDO activity as a surrogate), and downstream T cell polarization. Using gene silencing and a selection of microRNA mimics, we could successfully suppress or induce the expression of miR-511-3p in DCs. Consequently, we show for the first time, to our knowledge, that inhibition and/or overexpression of miR-511-3p has opposing effects on the expression levels of two key C-type lectin receptors, namely the mannose receptor and DC-specific ICAM 3 nonintegrin at protein and mRNA levels, thereby affecting C-type lectin receptor-induced modulation of IDO activity in DCs. Furthermore, we show that downregulation of miR-511-3p drives an anti-inflammatory DC response characterized by IL-10 production. Interestingly, the miR-511-3p^low DCs also promoted IL-4 secretion and suppressed IL-17 in cocultures with autologous T cells. Together, our data highlight the potential role of miR-511 in regulating DC function and downstream events leading to Th polarization and immune modulation.

Association between CLEC4E gene polymorphism of mincle and pulmonary tuberculosis infection in a northern Chinese population

BACKGROUND

Pulmonary tuberculosis caused by an intracellular pathogen, Mycobacterium tuberculosis continues to exist as a hazardous disease to human life globally. Genetic polymorphisms regulate resistance and susceptibility to tuberculosis. The C-type lectin receptor of family 4 member E (CLEC4E) confers protection against tuberculosis in laboratory animals but its function in influencing exposure or resistance to pulmonary tuberculosis (PTB) in humans remains obscure.

AIM

We conducted this research to analyze the effects or concomitance of CLEC4E gene variations with susceptibility to pulmonary tuberculosis in a northern Chinese population.

METHOD

In this study, 202 participants with pulmonary tuberculosis and 214 controls without PTB were enrolled. Two single nucleotide polymorphisms (SNPs) for CLEC4E on chromosome 12 were selected with a minor allele frequency of >0.05. All the SNPs were genotyped using high resolution melting analysis-PCR.

RESULTS

We estimated and compared two SNPs, rs10841845 and rs10841847. From our study findings, CLEC4E rs10841845 conferred protection against the development of pulmonary TB with a P value of <0.05 and odds ratio of <1 for all models of genetic inheritance. CLEC4E rs10841847 genotypes in co-dominant, Recessive, Dominant models and alleles had a significant statistical difference between patients and controls associated with resistance against the development of PTB (P<0.05 and OR<1).

CONCLUSION

Our findings suggest that variations at rs10841845 and rs10841847 of CLEC4E genes are associated with increased individual protection against PTB.

Endogenous Nucleic Acid Recognition by RIG-I-Like Receptors and cGAS

The innate immune defense of mammalian hosts relies on its capacity to detect invading pathogens and then directly eliminate them or help guide adaptive immune responses. Recognition of microbial DNA and RNA by pattern recognition receptors (PRRs) is central to the detection of pathogens by initiating cytokine-mediated innate immunity. In contrast, disturbance of this pathogen surveillance system can result in aberrant innate immune activation, leading to proinflammatory or autoimmune diseases. Among the many important PRRs are proteins of the retinoic acid-inducible gene-I (RIG-I)-like receptor (RLR) family as well as cyclic GMP-AMP synthase (cGAS), which detect viral RNA and DNA, respectively, within the host cell. Intriguingly, recent evidence has shown that "unmasked," misprocessed, or mislocalized host-derived RNA or DNA molecules can also be recognized by RLRs or cGAS, thereby triggering antiviral host defenses or causing inflammation. Here, we review recent advances of endogenous nucleic acid recognition by RLRs and cGAS during viral infection and systemic proinflammatory/autoimmune disorders.

Fungal Translocation Is Associated with Immune Activation and Systemic Inflammation in Treated HIV

The mechanisms causing HIV-associated immune activation remain incompletely understood. Alteration of intestinal integrity with subsequent translocation of bacterial products appears to play an important role; however, little is known about the impact of fungal translocation. We assessed the effect of fungal translocation and its association with immune activation in people living with HIV (PLWH) compared with uninfected controls. We measured serum levels of β-D-glucan (BDG) and anti-Saccharomyces cerevisiae antibodies (ASCA) immunoglobulin G (IgG) and immunoglobulin A (IgA) and markers of systemic inflammation and immune activation in virally suppressed PLWH on antiretroviral therapy (ART) and uninfected controls. T-test and Mann-Whitney tests were used to compare markers by HIV status and correlation and regression analyses were used to assess associations of fungal translocation markers with markers of inflammation. One hundred seventy-six participants were included (128 HIV+ and 48 HIV-); 72% male, 65% African American, median age was 50 years, and CD4 was 710 cells/cm³. Levels of BDG tended to be lower in HIV+ when compared with controls (p = .05). No significant difference in levels of ASCA IgG and IgA was seen between groups (p > .75). There was a significant correlation between BDG and several markers of inflammation and immune activation in PLWH, not seen in uninfected controls. In contrast, no correlations were seen between levels of ASCA IgG and IgA with inflammatory markers. PLWH on ART do not have higher levels of BDG or ASCA when compared with uninfected controls, however, the association found between BDG and several inflammation markers suggests a potential role of fungal translocation in the heightened immune activation seen in treated HIV.

Mammalian sugar-binding receptors: known functions and unexplored roles

Mammalian glycan-binding receptors, sometimes known as lectins, interact with glycans, the oligosaccharide portions of endogenous mammalian glycoproteins and glycolipids as well as sugars on the surfaces of microbes. These receptors guide glycoproteins out of and back into cells, facilitate communication between cells through both adhesion and signaling, and allow the innate immune system to respond quickly to viral, fungal, bacterial, and parasitic pathogens. For many of the roughly 100 glycan-binding receptors that are known in humans, there are good descriptions of what types of glycans they bind and how selectivity for these ligands is achieved at the molecular level. In some cases, there is also comprehensive evidence for the roles that the receptors play at the cellular and organismal levels. In addition to highlighting these well-understood paradigms for glycan-binding receptors, this review will suggest where gaps remain in our understanding of the physiological functions that they can serve.

Macrophage Phosphoproteome Analysis Reveals MINCLE-dependent and -independent Mycobacterial Cord Factor Signaling

Immune sensing of Mycobacterium tuberculosis relies on recognition by macrophages. Mycobacterial cord factor, trehalose-6,6'-dimycolate (TDM), is the most abundant cell wall glycolipid and binds to the C-type lectin receptor (CLR) MINCLE. To explore the kinase signaling linking the TDM-MINCLE interaction to gene expression, we employed quantitative phosphoproteome analysis. TDM caused upregulation of 6.7% and suppressed 3.8% of the 14,000 phospho-sites identified on 3727 proteins. MINCLE-dependent phosphorylation was observed for canonical players of CLR signaling (e.g. PLCγ, PKCδ), and was enriched for PKCδ and GSK3 kinase motifs. MINCLE-dependent activation of the PI3K-AKT-GSK3 pathway contributed to inflammatory gene expression and required the PI3K regulatory subunit p85α. Unexpectedly, a substantial fraction of TDM-induced phosphorylation was MINCLE-independent, a finding paralleled by transcriptome data. Bioinformatics analysis of both data sets concurred in the requirement for MINCLE for innate immune response pathways and processes. In contrast, MINCLE-independent phosphorylation and transcriptome responses were linked to cell cycle regulation. Collectively, our global analyses show substantial reprogramming of macrophages by TDM and reveal a dichotomy of MINCLE-dependent and -independent signaling linked to distinct biological responses.

Calcineurin inhibitors reduce NFAT-dependent expression of antifungal pentraxin-3 by human monocytes

Calcineurin (CN) inhibitors are effective clinical immunosuppressants but leave patients vulnerable to potentially fatal fungal infections. This study tested the hypothesis that CN inhibition interferes with antifungal immune defenses mediated by monocytes. We showed that NFAT is expressed by human monocytes, and is activated by exposure to fungal ligands. We confirmed that NFAT translocation potently activated target gene transcription using a human monocytic reporter cell line. Inhibition of CN‐NFAT by cyclosporine A significantly reduced monocyte production of TNF‐α, IL‐10, and MCP‐1 proteins in response to pattern recognition receptor ligands as well as to Aspergillus fumigatus conidia. Moreover, we revealed that human monocytes express the antifungal protein pentraxin‐3 under control of NFAT. In conclusion, clinical CN inhibitors have the potential to interfere with the novel NFAT‐dependent pentraxin‐3 pathway as well as antifungal cytokine production in human monocytes, thereby impeding monocyte‐mediated defenses against fungal infection in immune‐suppressed patients.

Comparative study on pattern recognition receptors in non-teleost ray-finned fishes and their evolutionary significance in primitive vertebrates

Pattern recognition receptors (PRRs) play important roles in innate immunity system and trigger the specific pathogen recognition by detecting the pathogen-associated molecular patterns. The main four PRRs components including Toll-like receptors (TLRs), RIG-I-like receptors (RLRs), NOD-like receptors (NLRs) and C-type lectin receptors (CLRs) were surveyed in the five genomes of non-teleost ray-finned fishes (NTR) including bichir (Polypterus senegalus), American paddlefish (Polyodon spathula), alligator gar (Atractosteus spatula), spotted gar (Lepisosteus oculatus) and bowfin (Amia calva), representing all the four major basal groups of ray-finned fishes. The result indicates that all the four PRRs components have been well established in these NTR fishes. In the RLR-MAVS signal pathway, which detects intracellular RNA ligands to induce production of type I interferons (IFNs), the MAVS was lost in bichir particularly. Also, the essential genes of recognition of Lipopolysaccharide (LPS) commonly in mammals like MD2, LY96 and LBP could not be identified in NTR fishes. It is speculated that TLR4 in NTR fishes may act as a cooperator with other PRRs and has a different pathway of recognizing LPS compared with that in mammals. In addition, we provide a survey of NLR and CLR in NTR fishes. The CLRs results suggest that Group V receptors are absent in fishes and Group II and VI receptors are well established in the early vertebrate evolution. Our comprehensive research of PRRs involving NTR fishes provides a new insight into PRR evolution in primitive vertebrate.

Genetic defects in fungal recognition and susceptibility to invasive pulmonary aspergillosis

The interindividual variability in the onset and clinical course of invasive pulmonary aspergillosis (IPA) raises fundamental questions about its actual pathogenesis. Clinical and epidemiological studies have reported only a few examples of monogenic defects, however an expanding number of common polymorphisms associated with IPA has been identified. Understanding how genetic variation regulates the immune response to Aspergillus provides critical insights into the human immunobiology of IPA by pinpointing directly relevant immune molecules and interacting pathways. Most of the genetic defects reported to increase susceptibility to infection were described or suggested to impair fungal recognition by the innate immune system. In this review, we discuss the contribution of host genetic variation in pattern recognition receptors to the development of IPA. An improved understanding of the molecular and cellular processes that regulate human susceptibility to IPA is ultimately expected to pave the way toward personalized medical interventions based on host-directed risk stratification and individualized immunotherapy.

Use of Dendritic Cell Receptors as Targets for Enhancing Anti-Cancer Immune Responses

A successful anti-cancer vaccine construct depends on its ability to induce humoral and cellular immunity against a specific antigen. Targeting receptors of dendritic cells to promote the loading of cancer antigen through an antibody-mediated antigen uptake mechanism is a promising strategy in cancer immunotherapy. Researchers have been targeting different dendritic cell receptors such as Fc receptors (FcR), various C-type lectin-like receptors such as dendritic and thymic epithelial cell-205 (DEC-205), dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN), and Dectin-1 to enhance the uptake process and subsequent presentation of antigen to T cells through major histocompatibility complex (MHC) molecules. In this review, we compare different subtypes of dendritic cells, current knowledge on some important receptors of dendritic cells, and recent articles on targeting those receptors for anti-cancer immune responses in mouse models.

Deletion of hematopoietic Dectin-2 or CARD9 does not protect against atherosclerotic plaque formation in hyperlipidemic mice

Inflammatory reactions activated by pattern recognition receptors (PRRs) on the membrane of innate immune cells play an important role in atherosclerosis. Whether the PRRs of the C-type lectin receptor (CLR) family including Dectin-2 may be involved in the pathogenesis of atherosclerosis remains largely unknown. Recently, the CLR-adaptor molecule caspase recruitment domain family member 9 (CARD9) has been suggested to play a role in cardiovascular pathologies as it provides the link between CLR activation and transcription of inflammatory cytokines as well as immune cell recruitment. We therefore evaluated whether hematopoietic deletion of Dectin-2 or CARD9 reduces inflammation and atherosclerosis development. Low-density lipoprotein receptor (Ldlr)-knockout mice were transplanted with bone marrow from wild-type, Dectin-2- or Card9-knockout mice and fed a Western-type diet containing 0.1% (w/w) cholesterol. After 10 weeks, lipid and inflammatory parameters were measured and atherosclerosis development was determined. Deletion of hematopoietic Dectin-2 or CARD9 did not influence plasma triglyceride and cholesterol levels. Deletion of hematopoietic Dectin-2 did not affect atherosclerotic lesion area, immune cell composition, ex vivo cytokine secretion by peritoneal cells or bone marrow derived macrophages. Unexpectedly, deletion of hematopoietic CARD9 increased atherosclerotic lesion formation and lesion severity. Deletion of hematopoietic CARD9 did also not influence circulating immune cell composition and peripheral cytokine secretion. Besides a tendency to a reduced macrophage content within these lesions, plasma MCP-1 levels decreased upon WTD feeding. Deletion of hematopoietic Dectin-2 did not influence atherosclerosis development in hyperlipidemic mice. The absence of CARD9 unexpectedly increased atherosclerotic lesion size and severity, suggesting that the presence of CARD9 may protect against initiation of atherosclerosis development.

A low-density lipoprotein receptor (LDLR) class A domain-containing C-type lectin from Litopenaeus vannamei plays opposite roles in antibacterial and antiviral responses

C-type lectins (CTLs) are a group of pattern recognition receptors (PRRs) that contain carbohydrate recognition domains and play important roles in innate immunity. CTLs that contain an additional low-density lipoprotein receptor (LDLR) class A domain (LdlrCTL) have been identified in many crustaceans, but their functions in immune responses are mostly unknown. In this study, a novel LdlrCTL was identified from pacific white shrimp Litopenaeus vannamei (LvLdlrCTL), which showed high homology with previously reported crustacean LdlrCTLs. LvLdlrCTL was highly expressed in hemocytes and its expression was up-regulated after immune stimulations. Silencing of LdlrCTL significantly promoted infection of shrimp by Vibrio parahaemolyticus but inhibited infection by white spot syndrome virus (WSSV), suggesting that LdlrCTL could play opposite roles in antibacterial and antiviral responses. LdlrCTL exhibited agglutination activity against bacteria and fungi and could potentiate the phagocytosis of hemocytes. Moreover, the expression of many immune effector genes and signalling pathway components was significantly changed in LdlrCTL-silenced shrimp, indicating that LdlrCTL could be involved in immune regulation.

Long noncoding RNA Malat1 regulates differential activation of macrophages and response to lung injury

Macrophage activation, i.e., classical M1 and the alternative M2, plays a critical role in many pathophysiological processes, such as inflammation and tissue injury and repair. Although the regulation of macrophage activation has been under extensive investigation, there is little knowledge about the role of long noncoding RNAs (lncRNAs) in this event. In this study, we found that lncRNA Malat1 expression is distinctly regulated in differentially activated macrophages in that it is upregulated in LPS-treated and downregulated in IL-4-treated cells. Malat1 knockdown attenuates LPS-induced M1 macrophage activation. In contrast, Malat1 knockdown enhanced IL-4-activated M2 differentiation as well as a macrophage profibrotic phenotype. Mechanistically, Malat1 knockdown led to decreased expression of Clec16a, silencing of which phenocopied the regulatory effect of Malat1 on M1 activation. Interestingly, Malat1 knockdown promoted IL-4 induction of mitochondrial pyruvate carriers (MPCs) and their mediation of glucose-derived oxidative phosphorylation (OxPhos), which was crucial to the Malat1 regulation of M2 differentiation and profibrotic phenotype. Furthermore, mice with either global or conditional myeloid knockout of Malat1 demonstrated diminished LPS-induced systemic and pulmonary inflammation and injury. In contrast, these mice developed more severe bleomycin-induced lung fibrosis, accompanied by alveolar macrophages displaying augmented M2 and profibrotic phenotypes. In summary, we have identified what we believe is a previously unrecognized role of Malat1 in the regulation of macrophage polarization. Our data demonstrate that Malat1 is involved in pulmonary pathogeneses in association with aberrant macrophage activation.

The critical role of Dectin-1 in host controlling systemic Candida krusei infection

There are increasing invasive fungal infections associated with non-albicans, which causes mortal infections in immune deficiency population. Candida krusei is a major non-albicans that exhibits intrinsic resistance to fluconazole and makes clinical treatment difficult. Previous studies revealed that C-type lectin receptors (CLRs) Dectin-1 plays critical roles in host defense against C. albicans infections. C. krusei and C. albicans are phylogenetically different although in the same genus. Whether Dectin-1 contributes to host immune response against C. krusei infection is still unknown. In the present study, we explored the potential roles of the Dectin-1 in host defense against C. krusei. We found that Dectin-1 ligand β-(1,3)-glucan markedly exposed on the cell surface of C. krusei, while β-(1,3)-glucan of C. albicans is masked. Dectin-1 is required for host myeloid cells recognition, killing of C. krusei, and development of subsequent Th1 and Th17 cell-mediated adaptive immune response. Furthermore, Dectin-1-deficient mice (Dectin-1^-/- ) are more susceptible to C. krusei infection. Together, we confirmed the important roles of Dectin-1 in host defense against C. krusei infection, demonstrating a previously unknown mechanism for C. krusei infection. Our study, therefore, provides a further understanding of host immune response against C. krusei.

Innate Immune Signaling and Its Role in Metabolic and Cardiovascular Diseases

The innate immune system is an evolutionarily conserved system that senses and defends against infection and irritation. Innate immune signaling is a complex cascade that quickly recognizes infectious threats through multiple germline-encoded cell surface or cytoplasmic receptors and transmits signals for the deployment of proper countermeasures through adaptors, kinases, and transcription factors, resulting in the production of cytokines. As the first response of the innate immune system to pathogenic signals, inflammatory responses must be rapid and specific to establish a physical barrier against the spread of infection and must subsequently be terminated once the pathogens have been cleared. Long-lasting and low-grade chronic inflammation is a distinguishing feature of type 2 diabetes and cardiovascular diseases, which are currently major public health problems. Cardiometabolic stress-induced inflammatory responses activate innate immune signaling, which directly contributes to the development of cardiometabolic diseases. Additionally, although the innate immune elements are highly conserved in higher-order jawed vertebrates, lower-grade jawless vertebrates lack several transcription factors and inflammatory cytokine genes downstream of the Toll-like receptors (TLRs) and retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) pathways, suggesting that innate immune signaling components may additionally function in an immune-independent way. Notably, recent studies from our group and others have revealed that innate immune signaling can function as a vital regulator of cardiometabolic homeostasis independent of its immune function. Therefore, further investigation of innate immune signaling in cardiometabolic systems may facilitate the discovery of new strategies to manage the initiation and progression of cardiometabolic disorders, leading to better treatments for these diseases. In this review, we summarize the current progress in innate immune signaling studies and the regulatory function of innate immunity in cardiometabolic diseases. Notably, we highlight the immune-independent effects of innate immune signaling components on the development of cardiometabolic disorders.

Dectin-1 Contributes to Myocardial Ischemia/Reperfusion Injury by Regulating Macrophage Polarization and Neutrophil Infiltration

BACKGROUND

Macrophage-associated immune response plays an important role in myocardial ischemia/reperfusion (IR) injury. Dectin-1, expressed mainly on activated myeloid cells, is crucial for the regulation of immune homeostasis as a pattern recognition receptor. However, its effects and roles during the myocardial IR injury remain unknown.

METHODS

Genetic ablation, antibody blockade, or Dectin-1 activation, along with the adoptive bone marrow transfer chimeric model, was used to determine the functional significance of Dectin-1 in myocardial IR injury. Immune cell filtration and inflammation were examined by flow cytometry, quantitative real-time polymerase chain reaction, and immunohistochemistry. Moreover, Dectin-1⁺ cells were analyzed by flow cytometry in the blood of patients with ST-segment-elevation myocardial infarction and stable patients with normal coronary artery (control).

RESULTS

We demonstrated that Dectin-1 expression observed on the bone marrow-derived macrophages is increased in the heart during the early phase after IR injury. Dectin-1 deficiency and antibody-mediated Dectin-1 inhibition led to a considerable improvement in cardiac function, accompanied by a reduction in cardiomyocyte apoptosis, which was associated with a decrease in M1 macrophage polarization and Ly-6C⁺ monocyte and neutrophil infiltration. Activation of Dectin-1 with its agonist had the opposite effects. Furthermore, Dectin-1 contributed to neutrophil recruitment through the regulation of Cxcl1 and granulocyte colony-stimulating factor expression. In addition, Dectin-1-dependent interleukin-23/interleukin-1β production was shown to be essential for interleukin-17A expression by γδT cells, leading to neutrophil recruitment and myocardial IR injury. Furthermore, we demonstrated that circulating Dectin-1⁺CD14⁺⁺CD16^- and Dectin-1⁺CD14⁺⁺CD16⁺ monocyte levels were significantly higher in patients with ST-segment-elevation myocardial infarction than in controls and positively correlated with the severity of cardiac dysfunction.

CONCLUSIONS

Our results reveal a crucial role of Dectin-1 in the process of mouse myocardial IR injury and provide a new, clinically significant therapeutic target.

mKLRL1 regulates the maturation of dendritic cells and plays important roles in immune tolerance

KLRL1 is a member of C-type lectin-like receptors (CLEC) and preferentially expressed on the surface of immune cells. We have previously illustrated its inhibitory role in Natural killer (NK) cells. Though cloned from dendritic cells (DCs), its role in DCs has not been fully identified. Here, we found that mKLRL1 markedly decreased during DC maturation; mKLRL1-modifed DCs showed enhanced phagocytic capability and reduced ability to induce T cell proliferation, which mimics immature DCs. Further investigation revealed that IL-10 was indispensable for mKLRL1 to suppress DC maturation. And p38 activation was responsible for preferential IL-10 production. Pretreatment with mKLRL1-modified DCs protected mice from subsequently EAE induction, indicating a role in immune tolerance. Taken together, our results have revealed an inhibitory role of KLRL1 in mouse DCs.

Expression of C-type lectin receptor mRNA in otitis media with effusion and chronic otitis media with and without cholesteatoma

BACKGROUND & OBJECTIVES

C-type lectin receptors (CLRs) are a family of pattern recognition receptors (PRPs). The expression of CLRs has been analyzed in other diseases but has not yet been compared in patients with otitis media with effusion (OME), chronic otitis media (COM) and COM with cholesteatoma (Chole OM). This study therefore evaluated the levels of expression of mRNAs encoding Dectin-1, MR1, MR2, DC-SIGN, Syk, Card-9, Bcl-10, Malt-1, Src, DEC-205, Tim-3, Trem-1, and DAP-12 in patients with OME, COM, and Chole OM.

METHODS

CLR mRNA levels in patients with OME, COM, and Chole OM were assessed by real-time polymerase chain reaction. The level of expression of each mRNA was compared in patients with and without bacteria, and in patients with conductive hearing loss (CHL) and sensorineural hearing loss (SNHL).

RESULTS

The patterns of expression of CLRs differed in patients with OME, COM, and Chole OM. Galectin-1 mRNA level was significantly higher in the COM than in the Chole OM group (p<0.05), and MR1 and Galectin-1 mRNA levels among patients with CHL were significantly higher in those with COM than with Chole OM (p<0.05). Galectin-1 mRNA level among patients with SNHL was also significantly higher in the COM than in the Chole OM group (p<0.05).

CONCLUSIONS

The levels of expression of mRNAs encoding the CLRs Dectin-1, MR1, MR2, DC-SIGN, Syk, Card-9, Bcl-10, Malt-1, Src, DEC-205, Tim-3, Trem-1 and DAP-12 differ among patients with OME, COM, and Chole OM.

Synthesis and comparison of linear and hyperbranched multivalent glycosides for C-type lectin binding

Hyperbranched and linear polyglycerol-based mannoside and fucosyllactoside residues with different ligand densities showed nanomolar binding affinities for MBL and DC-SIGN proteins.

Impact of the Environment upon the Candida albicans Cell Wall and Resultant Effects upon Immune Surveillance

The fungal cell wall is an essential organelle that maintains cellular morphology and protects the fungus from environmental insults. For fungal pathogens such as Candida albicans, it provides a degree of protection against attack by host immune defences. However, the cell wall also presents key epitopes that trigger host immunity and attractive targets for antifungal drugs. Rather than being a rigid shield, it has become clear that the fungal cell wall is an elastic organelle that permits rapid changes in cell volume and the transit of large liposomal particles such as extracellular vesicles. The fungal cell wall is also flexible in that it adapts to local environmental inputs, thereby enhancing the fitness of the fungus in these microenvironments. Recent evidence indicates that this cell wall adaptation affects host-fungus interactions by altering the exposure of major cell wall epitopes that are recognised by innate immune cells. Therefore, we discuss the impact of environmental adaptation upon fungal cell wall structure, and how this affects immune recognition, focussing on C. albicans and drawing parallels with other fungal pathogens.

Diverse Roles of DEAD/DEAH-Box Helicases in Innate Immunity and Diseases

DEAD/DEAH-box helicases are enzymes that belong to the DEAD/H-box family of SF2 helicase superfamily. These enzymes are essential in RNA metabolism, where they are involved in a number of processes that require manipulation of RNA structure. Recent studies have found that some DEAD/DEAH-box helicases play important roles in innate immunity, where they act as sensors of cytosolic DNA/RNA, as adaptor proteins, or as regulators of signaling and gene expression. In spite of their function in immunity, DEAD/DEAH-box helicases can also be hijacked and exploited by viruses to circumvent detection and aid in viral replication. These findings not only imply that DEAD/DEAH-box helicases have a broader function than previously thought, but also give us a much better understanding of immune mechanisms and diseases that arise due to the dysregulation or evasion thereof. In this chapter, we demonstrate the known scope of activities of human DEAD/DEAH-box helicases in innate immunity and interaction with viruses or other pathogens. Additionally, we give an outline of diseases in which they are, or may be, involved in the context of immunity.

The hepatic lectin of zebrafish binds a wide range of bacteria and participates in immune defense

C-type lectins (CTLs) have a diverse range of functions including cell-cell adhesion, immune response to pathogens and apoptosis. Asialoglycoprotein receptor (ASGPR), also known as hepatic lectin, a member of CTLs, was the first animal lectin identified, yet information regarding it remains rather limited in teleost. In this study, we identified a putative protein in zebrafish, named as the zebrafish hepatic lectin (Zhl). The zhl encoded a typical Ca²⁺-dependent carbohydrate-binding protein, and was mainly expressed in the liver in a tissue specific fashion. Challenge with LPS and LTA resulted in significant up-regulation of zhl expression, suggesting involvement in immune response. Actually, recombinant C-type lectin domain (rCTLD) of Zhl was found to be capable of agglutinating and binding to both Gram-negative and Gram-positive bacteria and enhancing the phagocytosis of the bacteria by macrophages. Moreover, rCTLD specifically bound to insoluble lipopolysaccharide (LPS), lipoteichoic acid (LTA) and peptidoglycan (PGN), which were inhibited by galactose. Interestingly, Zhl was located in the membrane, and its overexpression could inhibit the production of pre-inflammatory cytokines. Taken together, these results indicate that Zhl has immune activity capable of defending invading pathogens, enriching our understanding of the function of ASGPR/hepatic lectin.

Neutrophil Caspase-11 Is Required for Cleavage of Caspase-1 and Secretion of IL-1β in Aspergillus fumigatus Infection

Neutrophils are an important source of IL-1β secretion in bacterial infections, where they infiltrate affected tissues in log-fold higher numbers than macrophages. Neutrophils also have functional NLRP3 and NLRC4 inflammasomes that can process pro-IL-1β to the bioactive 17-kDa form. In the current study, we examined the role of IL-1β in response to corneal infection with the filamentous fungus Aspergillus fumigatus and found that neutrophils were the predominant source of bioactive IL-1β in the cornea. We also observed that caspase-11^-/- mice exhibit the same susceptibility phenotype as IL-1β^-/-, ASC^-/-, NLRP3^-/-, and caspase-1^-/- mice, with impaired neutrophil recruitment to infected corneas and increased hyphal growth. We further demonstrate that caspase-11 is required for caspase-1 activation and IL-1β processing during infection. In vitro, we show that caspase-11 is regulated by the common type I IFN receptor (IFNAR) through JAK-STAT signaling and that caspase-11 is required for speck formation and caspase-1 activity. Aspergillus spores (conidia) stimulate IL-1β processing and secretion in neutrophils activation of Dectin-1 and signaling through the Raf1 kinase/MEKK rather than the spleen tyrosine kinase pathway. Collectively, these findings reveal unexpected regulation of IL-1β production by neutrophils in response to pathogenic fungi.

The first line of defence: insights into mechanisms and relevance of phagocytosis in epithelial cells

Epithelial tissues cover most of the external and internal surfaces of the body and its organs. Inevitably, these tissues serve as first line of defence against inorganic, organic, and microbial intruders. Epithelial cells are the main cell type of these tissues. Besides their function as cellular barrier, there is growing evidence that epithelial cells are of particular relevance as initial sensors of danger and also as executers of adequate defence responses. These cells feature various essential functions to maintain tissue integrity in health and disease. In this review, we survey some of the different innate immune functions of epithelial cells in mucosal tissues being constantly exposed to a plethora of harmless contaminants but also of pathogens. We discuss how epithelial cells avoid inadequate immune responses in such conditions. In particular, we will focus on the diverse types and mechanisms of phagocytosis used by epithelial cells to not only maintain homeostasis but to also harness the host response against invading pathogens.

YesU from Bacillus subtilis preferentially binds fucosylated glycans

The interaction of carbohydrate-binding proteins (CBPs) with their corresponding glycan ligands is challenging to study both experimentally and computationally. This is in part due to their low binding affinity, high flexibility, and the lack of a linear sequence in carbohydrates, as exists in nucleic acids and proteins. We recently described a function-prediction technique called SPOT-Struc that identifies CBPs by global structural alignment and binding-affinity prediction. Here we experimentally determined the carbohydrate specificity and binding affinity of YesU (RCSB PDB ID: 1oq1), an uncharacterized protein from Bacillus subtilis that SPOT-Struc predicted would bind high mannose-type glycans. Glycan array analyses however revealed glycan binding patterns similar to those exhibited by fucose (Fuc)-binding lectins, with SPR analysis revealing high affinity binding to Lewis^x and lacto-N-fucopentaose III. Structure based alignment of YesU revealed high similarity to the legume lectins UEA-I and GS-IV, and docking of Lewis^x into YesU revealed a complex structure model with predicted binding affinity of −4.3 kcal/mol. Moreover the adherence of B. subtilis to intestinal cells was significantly inhibited by Le^x and Le^y but by not non-fucosylated glycans, suggesting the interaction of YesU to fucosylated glycans may be involved in the adhesion of B. subtilis to the gastrointestinal tract of mammals.

Wnt5a contributes to dectin-1 and LOX-1 induced host inflammatory response signature in Aspergillus fumigatus keratitis

Fungal keratitis causes devastating corneal ulcers which can result in significant visual impairment and even blindness. As a ligand that activates the non-canonical Wnt signaling pathways, Wnt5a triggers the production of important inflammatory chemokines and the chemotactic migration of neutrophils. In this study we aimed to characterize the role of Wnt5a production, in situ, in vivo and in vitro in response to fungal keratitis. Wnt5a expression in corneas of Aspergillus fumigatus (A. fumigatus) keratitis patients was determined by quantitative polymerase chain reaction (qRT-PCR) and immunofluorescence. In vivo and in vitro experiments were then performed in mouse models and THP-1 macrophages cell cultures infected with A. fumigatus, respectively. C57BL/6 mice were pretreated with siRNAs or neutralizing antibodies for dectin-1, LOX-1 and Wnt5a, or inhibitors of erk1/2 and JNK. Changes in Wnt5a expression were assessed by clinical evaluation, qRT-PCR, immunofluorescence, western blot and bioluminescence imaging system image acquisition. We confirmed that corneal Wnt5a expression increased with A. fumigatus keratitis in patients and a murine model. Wnt5a production was dependent on dectin-1 and LOX-1 expression with contributions by Erk1/2 and JNK pathways. Additionally, Wnt5a knockdown revealed decreased levels of MPO, lower neutrophil recruitment, and a higher fungal load in mouse models. Compared with controls, Wnt5a knockdown impaired pro-inflammatory cytokine IL-1β production in response to A. fumigatus exposure. Wnt5a also produces dectin-1 and LOX-1 induced inflammatory signature via effective neutrophil recruitment and inflammatory cytokine production in response to A. fumigatus keratitis. These findings demonstrate that Wnt5a is a critical component of the antifungal immune response.

Dectin-1 on macrophages modulates the immune response to Fasciola hepatica products through the ERK signaling pathway

Fasciolosis is a zoonotic disease of increasing importance due to its worldwide distribution and elevated economic losses. Previously, we demonstrated that Fasciola hepatica excretory-secretory products (FhESP) induce immunomodulatory effects on peritoneal macrophages in a Dectin-1 dependent manner. In this study, we observed that peritoneal macrophages from naive BALB/c mice stimulated in vitro with FhESP presented increased expression levels of phosphorylated extracellular-signal-regulated kinase (ERK), and this effect was dependent on Syk, protein kinase C (PKC) and Dectin-1. In this sense, we observed increased levels of arginase activity, IL-10 and TGF-β in macrophages stimulated with FhESP, which were dependent on PKC and ERK. Furthermore, we observed that the increased arginase activity, as well as in TGF-β and IL-10 levels, was partially dependent on IL-10 receptor signaling in macrophages that were pre-incubated with anti-IL10R before being stimulated with FhESP. Taken together, these results suggest the participation of Dectin-1 and Syk in FhESP interaction with peritoneal macrophages and the possible role of ERK and IL-10 in downstream signaling pathways involved in the immunomodulatory effects induced by Fasciola hepatica products.

β-(1,3)-Glucan derived from Candida albicans induces inflammatory cytokines from macrophages and lamina propria mononuclear cells derived from patients with Crohn's disease

Background/Aims

Recent research has highlighted the importance of interactions between commensal fungi and intestinal inflammation. However, there are few studies investigating whether commensal fungi contribute to inflammation in patients with Crohn's disease (CD). The aim of this study is to investigate reveal interactions between commensal fungi and host immune cells in CD.

Methods

CD14-positive monocytes were isolated from peripheral blood mononuclear cells from healthy human volunteers and then differentiated in the presence of macrophage colony-stimulating factor (M-CSF) (referred to as M-macrophages, M-Mϕs) or M-CSF and interferon-γ (IFN-γ) (referred to as M-gamma macrophages, Mγ-Mϕs). Cytokine production by these in vitro differentiated macrophages in response to β-(1,3)-glucan was analyzed by flow cytometry. Expression of Dectin-1 was examined using flow cytometry, western blotting, and quantitative reverse transcription-polymerase chain reaction. Cytokine production by in vitro differentiated macrophages in response to β-(1,3)-glucan was measured in the presence of an anti-Dectin-1 receptor antagonist, anti-Syr, or an anti-Fas-1 antibody. Cytokine production by lamina propria mononuclear cells (LPMCs) derived from CD patients in response to β-(1,3)-glucan was also analyzed.

Results

Mγ-Mϕs produced a large amount of tumor necrosis factor-α (TNF-α) and interleukin-6 in response to β-(1,3)-glucan. Dectin-1 expression was significantly higher in Mγ-Mϕs than in M-Mϕs. The increase in TNF-α production by Mγ-Mϕs stimulated with glucan was reversed by blocking Dectin-1, Syr or Fas-1. LPMCs derived from CD patients stimulated with β-(1,3)-glucan produced significantly higher amount of TNF-α than LPMCs derived from UC patients.

Conclusions

These results suggest that commensal fungal microbiota may contribute to the pathogenesis of CD by inducing macrophages-derived pro-inflammatory cytokines.

Simultaneous quadruple-channel optical transduction of a nanosensor for multiplexed qualitative and quantitative analysis of lectins

A multichannel optical nanosensor capable of identifying and quantitating multiple lectins simultaneously was developed. The quadruple channel of fluorescence and scattering signals can be in situ collected from the same solution system, which offers high accuracy, discrimination resolution and measurement convenience. This nanosensor can in principle be generalized to the analysis of all lectins and saccharide binding organisms.

The Mycobacterial Adjuvant Analogue TDB Attenuates Neuroinflammation via Mincle-Independent PLC-γ1/PKC/ERK Signaling and Microglial Polarization

Microglial activation has long been recognized as a hallmark of neuroinflammation. Recently, the bacillus Calmette-Guerin (BCG) vaccine has been reported to exert neuroprotective effects against several neurodegenerative disorders. Trehalose-6,6'-dibehenate (TDB) is a synthetic analogue of trehalose-6,6'-dimycolate (TDM, also known as the mycobacterial cord factor) and is a new adjuvant of tuberculosis subunit vaccine currently in clinical trials. Both TDM and TDB can activate macrophages and dendritic cells through binding to C-type lectin receptor Mincle; however, its action mechanism in microglia and their relationship with neuroinflammation are still unknown. In this article, we found that TDB inhibited LPS-induced M1 microglial polarization in primary microglia and BV-2 cells. However, TDB itself had no effects on IKK, p38, and JNK activities or cytokine expression. In contrast, TDB activated ERK1/2 through PLC-γ1/PKC signaling and in turn decreased LPS-induced NF-κB nuclear translocation. Furthermore, TDB-induced AMPK activation via PLC-γ1/calcium/CaMKKβ-dependent pathway and thereby enhanced M2 gene expressions. Interestingly, knocking out Mincle did not alter the anti-inflammatory and M2 polarization effects of TDB in microglia. Conditional media from LPS-stimulated microglial cells can induce in vitro neurotoxicity, and this action was attenuated by TDB. Using a mouse neuroinflammation model, we found that TDB suppressed LPS-induced M1 microglial activation and sickness behavior, but promoted M2 microglial polarization in both WT and Mincle^-/- mice. Taken together, our results suggest that TDB can act independently of Mincle to inhibit LPS-induced inflammatory response through PLC-γ1/PKC/ERK signaling and promote microglial polarization towards M2 phenotype via PLC-γ1/calcium/CaMKKβ/AMPK pathway. Thus, TDB may be a promising therapeutic agent for the treatment of neuroinflammatory diseases.