Group XIV C-type lectins: emerging targets in tumor angiogenesis

C-type lectins, distinguished by a C-type lectin binding domain (CTLD), are an evolutionarily conserved superfamily of glycoproteins that are implicated in a broad range of physiologic processes. The group XIV subfamily of CTLDs are comprised of CD93, CD248/endosialin, CLEC14a, and thrombomodulin/CD141, and have important roles in creating and maintaining blood vessels, organizing extracellular matrix, and balancing pro- and anti-coagulative processes. As such, dysregulation in the expression and downstream signaling pathways of these proteins often lead to clinically relevant pathology. Recently, group XIV CTLDs have been shown to play significant roles in cancer progression, namely tumor angiogenesis and metastatic dissemination. Interest in therapeutically targeting tumor vasculature is increasing and the search for novel angiogenic targets is ongoing. Group XIV CTLDs have emerged as key moderators of tumor angiogenesis and metastasis, thus offering substantial therapeutic promise for the clinic. Herein, we review our current knowledge of group XIV CTLDs, discuss each's role in malignancy and associated potential therapeutic avenues, briefly discuss group XIV CTLDs in the context of two other relevant lectin families, and offer future direction in further elucidating mechanisms by which these proteins function and facilitate tumor growth.

A novel exoskeletal-derived C-type lectin facilitates phagocytosis of hemocytes in the oriental river prawn Macrobrachium nipponense

C-type lectins (CTLs) execute critical functions in multiple immune responses of crustaceans as a member of pattern recognition receptors (PRRs) family. In this study, a novel CTL was identified from the exoskeleton of the oriental river prawn Macrobrachium nipponense (MnLec3). The full-length cDNA of MnLec3 was 1150 bp with an open reading frame of 723 bp, encoding 240 amino acids. MnLec3 protein contained a signal peptide and one single carbohydrate-recognition domain (CRD). MnLec3 transcripts were widely distributed at the exoskeleton all over the body. Significant up-regulation of MnLec3 in exoskeleton after Aeromonas hydrophila challenged suggested the involvement of MnLec3 as well as the possible function of the exoskeleton in immune response. In vitro tests with recombinant MnLec3 protein (rMnLec3) manifested that it had polysaccharide binding activity, a wide spectrum of bacterial binding activity and agglutination activity only for tested Gram-negative bacteria (Escherichia coli, Vibrio anguillarum and A. hydrophila). Moreover, rMnLec3 significantly promoted phagocytic ability of hemocytes against A. hydrophila in vivo. What's more, MnLec3 interference remarkably impaired the survivability of the prawns when infected with A. hydrophila. Collectively, these results ascertained that MnLec3 derived from exoskeleton took an essential part in immune defense of the prawns against invading bacteria as a PRR.

The C-type lectin DCIR contributes to the immune response and pathogenesis of colorectal cancer

Development and progression of malignancies are accompanied and influenced by alterations in the surrounding immune microenvironment. Understanding the cellular and molecular interactions between immune cells and cancer cells has not only provided important fundamental insights into the disease, but has also led to the development of new immunotherapies. The C-type lectin Dendritic Cell ImmunoReceptor (DCIR) is primarily expressed by myeloid cells and is an important regulator of immune homeostasis, as demonstrated in various autoimmune, infectious and inflammatory contexts. Yet, the impact of DCIR on cancer development remains largely unknown. Analysis of available transcriptomic data of colorectal cancer (CRC) patients revealed that high DCIR gene expression is associated with improved patients' survival, immunologically "hot" tumors and high immunologic constant of rejection, thus arguing for a protective and immunoregulatory role of DCIR in CRC. In line with these correlative data, we found that deficiency of DCIR1, the murine homologue of human DCIR, leads to the development of significantly larger tumors in an orthotopic murine model of CRC. This phenotype is accompanied by an altered phenotype of tumor-associated macrophages (TAMs) and a reduction in the percentage of activated effector CD4+ and CD8+ T cells in CRC tumors of DCIR1-deficient mice. Overall, our results show that DCIR promotes antitumor immunity in CRC, making it an attractive target for the future development of immunotherapies to fight the second deadliest cancer in the world.

A novel C-type lectin protein (BjCTL5) interacts with apoptosis stimulating proteins of p53 (ASPP) to activate NF-κB signaling pathway in primitive chordate

C-type lectin proteins (CTLs), a group of pattern recognition receptors (PRRs), play pivotal roles in immune responses. However, the signal transduction and regulation of CTLs in cephalochordates have yet to be explored. In this study, we examined the composition of CTLs in Branchiostoma japonicum, identifying a total of 272 CTLs. These CTLs underwent further analysis concerning domain arrangement, tandem and segmental duplication events. A multidomain C-type lectin gene, designated as BjCTL5, encompassing CLECT, KR, CUB, MAM, and SR domains, was the focal point of our investigation. BjCTL5 exhibits ubiquitous expression across all detected tissues and is responsive to stimulation by LPS, mannose, and poly (I:C). The recombinant protein of BjCTL5 can bind to Escherichia coli and Staphylococcus aureus, inducing their agglutination and inhibiting the proliferation of S. aureus. Yeast two-hybrid, CoIP, and confocal immunofluorescence experiments revealed the interaction between BjCTL5 and apoptosis-stimulating proteins of p53, BjASPP. Intriguingly, BjCTL5 was observed to induce the luciferase activity of the NF-κB promoter in HEK293T cells. These results suggested a potential interaction between BjCTL5 and BjASPP, implicating that they involve in the activation of the NF-κB signaling pathway, which provides an evolutionary viewpoint on NF-κB signaling pathway in primitive chordate.

A CTL - Lys immune function maintains insect metamorphosis by preventing gut bacterial dysbiosis and limiting opportunistic infections

BACKGROUND

Gut bacteria are beneficial to the host, many of which must be passed on to host offspring. During metamorphosis, the midgut of holometabolous insects undergoes histolysis and remodeling, and thus risks losing gut bacteria. Strategies employed by holometabolous insects to minimize this risk are obscure. How gut bacteria affect host insects after entering the hemocoel and causing opportunistic infections remains largely elusive.

RESULTS

We used holometabolous Helicoverpa armigera as a model and found low Lactobacillus load, high level of a C-type lectin (CTL) gene CD209 antigen-like protein 2 (CD209) and its downstream lysozyme 1 (Lys1) in the midgut of the wandering stage. CD209 or Lys1 depletion increased the load of midgut Lactobacillus, which further translocate to the hemocoel. In particular, CD209 or Lys1 depletion, injection of Lactobacillus plantarum, or translocation of midgut L. plantarum into the hemocoel suppressed 20-hydroxyecdysone (20E) signaling and delayed pupariation. Injection of L. plantarum decreased triacylglycerol and cholesterol storage, which may result in insufficient energy and 20E available for pupariation. Further, Lysine-type peptidoglycan, the major component of gram-positive bacterial cell wall, contributed to delayed pupariation and decreased levels of triacylglycerols, cholesterols, and 20E, in both H. armigera and Drosophila melanogaster.

CONCLUSIONS

A mechanism by which (Lactobacillus-induced) opportunistic infections delay insect metamorphosis was found, namely by disturbing the homeostasis of lipid metabolism and reducing 20E production. Moreover, the immune function of CTL - Lys was characterized for insect metamorphosis by maintaining gut homeostasis and limiting the opportunistic infections.

Transcriptome Analysis of Meloidogyne javanica and the Role of a C-Type Lectin in Parasitism

Meloidogyne javanica is one of the most widespread and economically important sedentary endoparasites. In this study, a comparative transcriptome analysis of M. javanica between pre-parasitic second-stage juveniles (Pre-J2) and parasitic juveniles (Par-J3/J4) was conducted. A total of 48,698 unigenes were obtained, of which 18,826 genes showed significant differences in expression (p < 0.05). In the differentially expressed genes (DEGs) from transcriptome data at Par-J3/J4 and Pre-J2, a large number of unigenes were annotated to the C-type lectin (CTL, Mg01965), the cathepsin L-like protease (Mi-cpl-1), the venom allergen-like protein (Mi-mps-1), Map-1 and the cellulase (endo-β-1,4-glucanase). Among seven types of lectins found in the DEGs, there were 10 CTLs. The regulatory roles of Mj-CTL-1, Mj-CTL-2 and Mj-CTL-3 in plant immune responses involved in the parasitism of M. javanica were investigated. The results revealed that Mj-CTL-2 could suppress programmed cell death (PCD) triggered by Gpa2/RBP-1 and inhibit the flg22-stimulated ROS burst. In situ hybridization and developmental expression analyses showed that Mj-CTL-2 was specifically expressed in the subventral gland of M. javanica, and its expression was up-regulated at Pre-J2 of the nematode. In addition, in planta silencing of Mj-CTL-2 substantially increased the plant resistance to M. javanica. Moreover, yeast co-transformation and bimolecular fluorescence complementation assay showed that Mj-CTL-2 specifically interacted with the Solanum lycopersicum catalase, SlCAT2. It was demonstrated that M. javanica could suppress the innate immunity of plants through the peroxide system, thereby promoting parasitism.

PvMR1, a novel C-type lectin plays a crucial role in the antibacterial immune response of Pacific white shrimp, Penaeus vannamei

C-type lectins (CTLs) are important immune molecules in innate immune, which participate in non-self recognition and clearance of pathogens. Here, a new CTL with two distinct C-type lectin domains (CTLDs) from Pacific white shrimp Penaeus vannamei, designated as PvMR1 was identified. The obtained PvMR1 coding sequence (CDS) was 1044 bp long encoding a protein with 347 amino acids. PvMR1 had two CTLD, a conserved mannose-specific EPN motif and a galactose-specific QPD motif, clustering into the same branch as the crustacean CTLs. PvMR1 was widely distributed in shrimp tissues with the highest transcription level in the hepatopancreas, with significantly induced mRNA expression on the hepatopancreas and intestines after immune challenge with Vibrio anguillarum. In vitro assays with recombinant PvMR1 (rPvMR1) protein revealed that it exhibited a wide range of antimicrobial activity, bacterial binding ability, and bacterial agglutination activity in a Ca2+-independent manner. Moreover, PvMR1 promoted bacterial phagocytosis in hemocytes. Furthermore, rPvMR1 treatment could significantly enhance the bacterial clearance in hemolymph and greatly improved the survival of shrimp under V. anguillarum infection in vivo. These results collectively suggest that PvMR1 plays an important role in antibacterial immune response of P. vannamei.

Lectin diversity and their positive roles in WSSV replication through regulation of calreticulin expression and inhibiting ALFs expression

In biological evolution, gene duplication (GD) generates new genes to facilitate new functions. C-type lectins (CTLs) in crayfish have been extended by GD to expand their family members. In this study, four CTL genes generated by GD were identified from Procambarus clarkii (PcLec1-4). Among these four genes, PcLec1 can also generate new isoforms with different numbers of tandem repeats through DNA slip mispairing. PcLec1-4 was widely expressed in multiple tissues. The expression levels of PcLec1-4 were upregulated in the intestine of P. clarkii upon white spot syndrome virus (WSSV) challenge at multiple time points. Further analysis indicated that GATA transcription factor regulated PcLec1-4 expression. RNA interference and recombinant PcLec1-4 protein injection experiments suggested that PcLec1-4 promoted the expression of calreticulin (PcCRT) and negatively regulated the expression of antimicrobial peptides, thereby promoting WSSV replication. This study contributes to the understanding of the function of CTLs produced by GD during WSSV invasion in crustaceans.

CLEC19A overexpression inhibits tumor cell proliferation/migration and promotes apoptosis concomitant suppression of PI3K/AKT/NF-κB signaling pathway in glioblastoma multiforme

BACKGROUND

GBM is the most frequent malignant primary brain tumor in humans. The CLEC19A is a member of the C-type lectin family, which has a high expression in brain tissue. Herein, we sought to carry out an in-depth analysis to pinpoint the role of CLEC19A expression in GBM.

METHODS

To determine the localization of CLEC19A, this protein was detected using Western blot, Immunocytochemistry/Immunofluorescence, and confocal microscopy imaging. CLEC19A expression in glioma cells and tissues was evaluated by qRT-PCR. Cell viability, proliferation, migration, and apoptosis were examined through MTT assay, CFSE assay, colony formation, wound healing assay, transwell test, and flow cytometry respectively after CLEC19A overexpression. The effect of CLEC19A overexpression on the PI3K/AKT/NF-κB signaling pathway was investigated using Western blot. An in vivo experiment substantiated the in vitro results using the glioblastoma rat models.

RESULTS

Our in-silico analysis using TCGA data and measuring CLEC19A expression level by qRT-PCR determined significantly lower expression of CLEC19A in human glioma tissues compared to healthy brain tissues. By employment of ICC/IF, confocal microscopy imaging, and Western blot we could show that CLEC19A is plausibly a secreted protein. Results obtained from several in vitro readouts showed that CLEC19A overexpression in U87 and C6 glioma cell lines is associated with the inhibition of cell proliferation, viability, and migration. Further, qRT-PCR and Western blot analysis showed CLEC19A overexpression could reduce the expression levels of PI3K, VEGFα, MMP2, and NF-κB and increase PTEN, TIMP3, RECK, and PDCD4 expression levels in glioma cell lines. Furthermore, flow cytometry results revealed that CLEC19A overexpression was associated with significant cell cycle arrest and promotion of apoptosis in glioma cell lines. Interestingly, using a glioma rat model we could substantiate that CLEC19A overexpression suppresses glioma tumor growth.

CONCLUSIONS

To our knowledge, this is the first report providing in-silico, molecular, cellular, and in vivo evidences on the role of CLEC19A as a putative tumor suppressor gene in GBM. These results enhance our understanding of the role of CLEC19A in glioma and warrant further exploration of CLEC19A as a potential therapeutic target for GBM.

Tentaclins-A Novel Family of Phage Receptor-Binding Proteins That Can Be Hypermutated by DGR Systems

Diversity-generating retroelements (DGRs) are prokaryotic systems providing rapid modification and adaptation of target proteins. In phages, the main targets of DGRs are receptor-binding proteins that are usually parts of tail structures and the variability of such host-recognizing structures enables phage adaptation to changes on the bacterial host surface. Sometimes, more than one target gene containing a hypermutated variable repeat (VR) can be found in phage DGRs. The role of mutagenesis of two functionally different genes is unclear. In this study, several phage genomes that contain DGRs with two target genes were found in the gut virome of healthy volunteers. Bioinformatics analysis of these genes indicated that they encode proteins with different topology; however, both proteins contain the C-type lectin (C-lec) domain with a hypermutated beta-hairpin on its surface. One of the target proteins belongs to a new family of proteins with a specific topology: N-terminal C-lec domain followed by one or more immunoglobulin domains. Proteins from the new family were named tentaclins after TENTACLe + proteIN. The genes encoding such proteins were found in the genomes of prophages and phages from the gut metagenomes. We hypothesized that tentaclins are involved in binding either to bacterial receptors or intestinal/immune cells.

A novel C-type lectin (SpccCTL) suppresses MCRV replication by binding viral protein and regulating antiviral peptides in Scylla paramamosain

Pattern recognition receptors (PRRs) play a crucial role in the recognition and activation of innate immune responses against invading microorganisms. This study characterizes a novel C-type lectin (CTL), SpccCTL. The cDNA sequence of SpccCTL has a full length of 1744 bp encoding a 338-amino acid protein. The predicted protein contains a signal peptide, a coiled-coil (CC) domain, and a CLECT domain. It shares more than 50 % similarity with a few CTLs with a CC domain in crustaceans. SpccCTL is highly expressed in gills and hemocytes and upregulated after MCRV challenge, suggesting that it may be involved in antiviral immunity. Recombinant SpccCTL (rSpccCTL) as well as two capsid proteins of MCRV (VP11 and VP12) were prepared. Pre-incubating MCRV virions with rSpccCTL significantly suppresses the proliferation of MCRV in mud crabs, compared with the control (treatment with GST protein), and the survival rate of mud crabs is also significantly decreased. Knockdown of SpccCTL significantly facilitates the proliferation of MCRV in mud crabs. These results reveal that SpccCTL plays an important role in antiviral immune response. GST pull-down assay result shows that rSpccCTL interacts specifically with VP11, but not to VP12. This result is further confirmed by a Co-IP assay. In addition, we found that silencing SpccCTL significantly inhibits the expression of four antimicrobial peptides (AMPs). Considering that these AMPs are members of anti-lipopolysaccharide factor family with potential antiviral activity, they are likely involved in immune defense against MCRV. Taken together, these findings clearly demonstrate that SpccCTL can recognize MCRV by binding viral capsid protein VP11 and regulate the expression of certain AMPs, suggesting that SpccCTL may function as a potential PRR playing an essential role in anti-MCRV immunity of mud crab. This study provides new insights into the antiviral immunity of crustaceans and the multifunctional characteristics of CTLs.

A C-type lectin with a single carbohydrate-recognition domain (CRD) containing unique QPN/WDD motifs from Tegillarca granosa is involved in the innate immune defense

C-type lectins (CTLs), a superfamily of Ca2+-dependent carbohydrate-recognition proteins, serve as pattern recognition receptors (PRRs) in the immune response of many species. However, little is currently known about the CTLs of the commercially and ecologically important bivalve species, blood clam (Tegillarca granosa). In this study, a CTL (designated as TgCTL-1) with a single carbohydrate-recognition domain (CRD) containing unique QPN/WDD motifs was identified in the blood clam through transcriptome and whole-genome searching. Multiple alignment and phylogenetic analysis strongly suggested that TgCTL-1 was a new member of the CTL superfamily. Expression analysis demonstrated that TgCTL-1 was highly expressed in the hemocytes and visceral mass of the clam under normal condition. In addition, the expression of TgCTL-1 was shown to be significantly up-regulated upon pathogen challenge. Moreover, the recombinant TgCTL-1 (rTgCTL-1) displayed agglutinating and binding activities against both the gram-positive and gram-negative bacteria tested in a Ca2+-dependent manner. Furthermore, it was found that the in vitro phagocytic activity of hemocytes was significantly enhanced by rTgCTL-1. In general, our results showed that TgCTL-1 was an inducible acute-phase secretory protein, playing crucial roles in recognizing, agglutinating, and binding to pathogenic bacteria as well as modulating phagocytic activity of hemocytes in the innate immune defense of blood clam.

Identification of potential biomarkers associated with CD4+ T cell infiltration in myocardial ischemia-reperfusion injury using bioinformation analysis

Background

Myocardial ischemia-reperfusion injury (MIRI) is often part of clinical events such as cardiac arrest, resuscitation, and reperfusion after coronary artery occlusion. Recently, more and more studies have shown that the immune microenvironment is an integral part of ischemia-reperfusion injury (IRI), and CD4+ T-cell infiltration plays an important role, but there are no relevant molecular targets for clinical diagnosis and treatment.

Methods

The transcriptome data and matched group information were retrieved from the Gene Expression Omnibus (GEO) database. The ImmuCellAI-mouse (Immune Cell Abundance Identifier for mouse) algorithm was used to calculate each symbol's CD4+ T cell infiltration score. The time period with the greatest change in the degree of CD4+ T cell infiltration [ischemia-reperfusion 6 hours (IR6h)-ischemia-reperfusion 24 hours (IR24h)] was selected for the next analysis. Weighted gene co-expression network analysis (WGCNA) and differential expression analysis were performed to screen out CD4+ T cell-related genes and from which the gene CLEC5A was screened for the highest correlation with CD4+ T cell infiltration. The potential regulatory mechanism of CD4+ T cells in MIRI was discussed through various enrichment analysis. Finally, we analyzed the expression and molecular function (MF) of CLEC5A and its related genes in MIRI.

Results

A total of 406 CD4+ T cell-related genes were obtained by intersecting the results of WGCNA and differential expression analysis. Functional enrichment analysis indicated that the CD4+ T cell-related genes were mainly involved in chemokine signaling pathway and cell cycle. By constructing a protein-protein interaction (PPI) network, a total of 12 hub genes were identified as candidate genes for further analysis. Through the correlation analysis between the 12 candidate genes found in the PPI network and CD4+ T cell infiltration fraction, we determined the core gene CLEC5A. Finally, a gene interaction network was constructed to decipher the biological functions of CLEC5A using GeneMANIA.

Conclusions

In this study, RNA sequencing (RNA-Seq) data at different time points after reperfusion were subjected to a series of bioinformatics methods such as PPI network, WGCNA module, etc., and CLEC5A, a pivotal gene associated with CD4+ T-cells, was found, which may serve as a new target for diagnosis or treatment.

Modified CLEC3A-Derived Antimicrobial Peptides Lead to Enhanced Antimicrobial Activity against Drug-Resistant Bacteria

Antimicrobial peptides (AMPs) represent a promising alternative to conventional antibiotics. Sequence changes can significantly improve the therapeutic properties of antimicrobial peptides. In our study, we apply different sequence modifications to enhance the performance of the CLEC3A-derived AMPs HT-16 and HT-47. We truncated their sequences, inserting a triple-glycine linker, adding an N-terminal tryptophan residue, and generating a D-amino acid variant, resulting in the generation of seven new peptides. We investigated their antimicrobial activity against gram-positive and gram-negative bacteria, their cytotoxicity to murine cells, and the biostability of the modified peptides in serum. We identified a novel antimicrobial peptide, WRK-30, with enhanced antimicrobial potency against S. aureus and MRSA. Additionally, WRK-30 was less cytotoxic to eukaryotic cells, allowing its application in higher concentrations in an in vivo setting. In conclusion, we identified a novel CLEC3A-derived antimicrobial peptide WRK-30 with significantly improved therapeutic properties and the potential to widen the repertoire of conventional antibiotics.

Functional characterization of Bombyx mori (Lepidoptera: Bombycidae) C-type lectin 5

C-type lectins (CTLs) are an important family of pattern recognition receptors (PRRs) that regulate immune responses. The CTL5 gene of the silkworm Bombyx mori L. (Lepidoptera: Bombycidae) encodes a protein comprised of 223 amino acids, containing a signal peptide and a carbohydrate recognition domain (CRD). Our previous study showed that CTL5 can facilitate the clearance of bacteria from larval hemocoel but the underlying mechanisms are unclear. In this study, we found that CTL5 was mainly expressed in fourth-instar larvae, adult moths, and the larval epidermis. CTL5 expression showed differential responses to both pathogenic stimuli and the molting hormone 20-hydroxyecdysone. The full-length (FL) and truncated (ΔN/ΔC/ΔNC) CTL5 recombinant proteins can bind to hemocytes, polysaccharides, bacteria, and spores of the entomopathogenic fungus Beauveria bassiana. Yeast 2-hybrid assays showed that the recombinant proteins can interact with integrin β2-β5 subunits. Recombinant proteins increased the phagocytic rate of hemocytes. Injection of recombinant CTL5 stimulated the expression of many immune genes in hemocytes, mainly antimicrobial peptides and immune signaling molecules. Additionally, transcriptomic sequencing of CTL5-stimulated hemocytes revealed 265 upregulated and 580 downregulated genes. Functional enrichment and the gene set enrichment analyses showed that differentially expressed genes were mainly enriched in innate immune responses and signaling. Our study suggests that CTL5 may act as an opsonin to enhance the clearance of pathogens by regulating both humoral and cellular responses.

Binding of Trichinella spiralis C-type lectin with syndecan-1 on intestinal epithelial cells mediates larval invasion of intestinal epithelium

C-type lectin (CTL) is a protein that binds to saccharides and plays an important role in parasite adhesion, host cell invasion and immune evasion. Previous studies showed that recombinant T. spiralis C-type lectin (rTsCTL) promotes larval invasion of intestinal epithelium cells (IEC), whereas anti-rTsCTL antibodies inhibits larval invasion. Syndecan-1 (SDC-1) is a member of the heparan sulfate proteoglycan family which is mainly expressed on the surface of IEC and in extracellular matrices where they interact with a plethora of ligands. SDC-1 has a principal role in maintaining cell morphogenesis, establishing cell-cell adhesions, and regulating the gut mucosal barrier. The aim of this study was to investigate whether rTsCTL binds to SDC-1 on IEC, and the binding of rTsCTL with SDC-1 promotes larval invasion and its mechanism. IFA results show that rTsCTL and SDC-1 co-localized on Caco-2 cell membrane. GST pull-down and Co-IP verified the direct interaction between rTsCTL and SDC-1 on Caco-2 cells. qPCR and Western blotting revealed that rTsCTL binding to SDC-1 increased the expression of SDC-1 and claudin-2, and reduced the expression of occludin and claudin-1 in Caco-2 cells incubated with rTsCTL via the STAT3 pathway. β-Xyloside (a syndecan-1 synthesis inhibitor) and Stattic (a STAT3 inhibitor) significantly inhibited rTsCTL binding to syndecan-1 in Caco-2 cells and activation of the STAT3 pathway, abrogated the effects of rTsCTL on the expression of gut tight junctions, and impeded larval invasion. The results demonstrate that binding of rTsCTL to SDC-1 on Caco-2 cells activated the STAT3 pathway, decreased gut tight junction expression, damaged the integrity of the gut epithelial barrier, and mediated T. spiralis invasion of the gut mucosa. TsCTL might be regarded as a candidate vaccine target against T. spiralis invasion and infection.

Zearalenone-14-glucoside specifically promotes dysplasia of Gut-Associated Lymphoid Tissue: A natural product for constructing intestinal nodular lymphatic hyperplasia model

INTRODUCTION

Zearalenone-14-glucoside (Z14G) is a modified mycotoxin that widely contaminates food across the world. Our preliminary experiment showed that Z14G degrades to zearalenone (ZEN) in the intestine exerting toxicity. Notably, oral administration of Z14G in rats induces intestinal nodular lymphatic hyperplasia.

OBJECTIVES

To investigate the mechanism of Z14G intestinal toxicity and how it differs from ZEN toxicity. We conducted a precise toxicology study on the intestine of rats exposed to Z14G and ZEN using multi-omics technology.

METHODS

Rats were exposed to ZEN (5 mg/kg), Z14G-L (5 mg/kg), Z14G-H (10 mg/kg), and pseudo germ free (PGF)-Z14G-H (10 mg/kg) for 14 days. Histopathological studies were performed on intestines from each group and compared. Metagenomic, metabolomic, and proteomic analyses were performed on rat feces, serum, and intestines, respectively.

RESULTS

Histopathological studies showed that Z14G exposure resulted in dysplasia of gut-associated lymphoid tissue (GALT) compared to ZEN exposure. The elimination of gut microbes in the PGF-Z14G-H group alleviated or eliminated Z14G-induced intestinal toxicity and GALT dysplasia. Metagenomic analysis revealed that Z14G exposure significantly promoted the proliferation of Bifidobacterium and Bacteroides compared to ZEN. Metabolomic analysis showed that Z14G exposure significantly reduced bile acid, while proteomic analysis found that Z14G exposure significantly reduced the expression of C-type lectins compared to ZEN.

CONCLUSIONS

Our experimental results and previous research suggest that Z14G is hydrolyzed to ZEN by Bifidobacterium and Bacteroides promoting their co-trophic proliferation. This leads to inactivation of lectins by hyperproliferative Bacteroides when ZEN caused intestinal involvement, resulting in abnormal lymphocyte homing and ultimately GALT dysplasia. It is noteworthy that Z14G is a promising model drug to establish rat models of intestinal nodular lymphatic hyperplasia (INLH), which is of great significance for studying the pathogenesis, drug screening and clinical application of INLH.

Characterization and functional analysis of a novel C-type lectin in blunt snout bream (Megalobrama amblycephala)

C-type lectins, one of the pattern recognition receptors (PRRs), play significant roles in innate immune responses through binding to the pathogen-associated molecular patterns (PAMPs) presented on surfaces of microorganisms. Here, a novel C-type lectin (named as MaCTL) from blunt snout bream (Megalobrama amblycephala) was cloned and characterized. The open reading frame (ORF) of MaCTL is 573 bp long encoding a putative protein of 190 amino acids (aa), which contains a typical feature of signal peptide at 1-23 aa, a characteristic CRD domain at 45-178 aa and a WND/EPN motif that is required for carbohydrates-binding specificity. Phylogenetic analysis indicated that MaCTL is a novel member of CTL family and possessed the highest similarity to that of grass carp (92.11%). The qRT-PCR analysis revealed that MaCTL expressed widely in all examined normal tissues, including heart, liver, spleen, kidney, head-kidney, gill, intestine and muscle, with the higher expression in the spleen, liver and muscle. The expression of MaCTL in spleen was significantly elevated, peaking at 9 h and 6 h after LPS stimulation and Aeromonas hydrophila challenge, respectively, suggesting its association with involvement in innate immune response. The recombinant MaCTL protein (rMaCTL) agglutinated markedly both Gram-positive (Staphylococcus aureus) and Gram-negative bacteria, including Escherichia coli, Vibrio anguillarum, Vibrio vulnificus and Aeromonas hydrophila, in a Ca2+-dependent manner. Meanwhile, rMaCTL showed the binding effects on the five bacteria and four carbohydrates, such as glucose, surose, LPS and PGN. Moreover, rMaCTL could remarkably inhibit the growth of three types of bacteria in vitro. Overall, the results obtained above demonstrated firmly that MaCTL binds to carbohydrates on the surface of diverse pathogens as a PRR and elicits antimicrobial responses, which shed new light on a better understanding of antibacterial functions of CTLs in teleost fish.

Identification, characterization, and agglutinating activity of a novel C-type lectin domain family 3 member B (CLEC3B) discovered in golden pompano, Trachinotus ovatus

The lectins are a large family of carbohydrate-binding proteins that play important roles in the innate immune response of various organisms. Although C-type lectin domain family 3 member B (CLEC3B), an important member of C-type lectin, has been well documented in humans and several other higher vertebrates, little is currently known about this molecule in economically important marine fish species. In this study, through transcriptomic and BLAST screening, a novel CLEC3B gene was identified in the golden pompano (Trachinotus ovatus). The T. ovatus CLEC3B (ToCLEC3B) was subsequently characterized by bioinformatic analysis and compared with those reported in other species. In addition, the expression patterns of ToCLEC3B in different tissues under normal condition and at different times post pathogen challenge were assessed. Furthermore, the agglutinating activity of ToCLEC3B with and without Ca2+ against different bacteria and blood cells of donor species were verified using the recombinant T. ovatus CLEC3B (rToCLEC3B). Our results demonstrated that ToCLEC3B is a Ca2+-dependent galactose-binding lectin with a single copy of carbohydrate recognition domain (CRD). Similar to CLEC3B reported in other species, the CRD domain of ToCLEC3B consists of two α-helices, six β-sheets, and four loops, forming two Ca2+- and a galactose-binding sites. According to the phylogenetic analysis, the ToCLEC3B was highly similar (similarity at 95.00%) to that of its relative, the greater amberjack (Seriola dumerili). The expression of ToCLEC3B was detected in all tissues examined under normal condition and was significantly up-regulated by injection of pathogenic microbes. In addition, the rToCLEC3B exhibited strong agglutinating activity against different bacteria and blood cells of donor species in the presence of Ca2+. Our results indicate that ToCLEC3B is a constitutive and inducible acute-phase immune factor in the host's innate immune response of T. ovatus.

Natural selection has driven the recurrent loss of an immunity gene that protects Drosophila against a major natural parasite

Polymorphisms in immunity genes can have large effects on susceptibility to infection. To understand the origins of this variation, we have investigated the genetic basis of resistance to the parasitoid wasp Leptopilina boulardi in Drosophila melanogaster. We found that increased expression of the gene lectin-24A after infection by parasitic wasps was associated with a faster cellular immune response and greatly increased rates of killing the parasite. lectin-24A encodes a protein that is strongly up-regulated in the fat body after infection and localizes to the surface of the parasite egg. In certain susceptible lines, a deletion upstream of the lectin-24A has largely abolished expression. Other mutations predicted to abolish the function of this gene have arisen recurrently in this gene, with multiple loss-of-expression alleles and premature stop codons segregating in natural populations. The frequency of these alleles varies greatly geographically, and in some southern African populations, natural selection has driven them near to fixation. We conclude that natural selection has favored the repeated loss of an important component of the immune system, suggesting that in some populations, a pleiotropic cost to lectin-24A expression outweighs the benefits of resistance.

A C-type lectin in saliva of Aedes albopictus (Diptera: Culicidae) bind and agglutinate microorganisms with broad spectrum

Via complex salivary mixture, mosquitos can intervene immune response and be helpful to transmit several viruses causing deadly human diseases. Some C-type lectins (CTLs) of mosquito have been reported to be pattern recognition receptor to either resist or promote pathogen invading. Here, we investigated the expression profile and agglutination function of an Aedes albopictus CTL (Aalb_CTL2) carrying a single carbohydrate-recognition domain (CRD) and WND/KPD motifs. The results showed that Aalb_CTL2 was found to be specifically expressed in mosquito saliva gland and its expression was not induced by blood-feeding. The recombinant Aalb_CTL2 (rAalb_CTL2) could agglutinate mouse erythrocytes in the presence of calcium and the agglutinating activity could be inhibited by EDTA. rAalb_CTL2 also displayed the sugar binding ability to D-mannose, D-galactose, D-glucose, and maltose. Furthermore, it was demonstrated that rAalb_CTL2 could bind and agglutinate Gram positive bacteria Staphylococcus aureus and Bacillus subtilis, Gram negative bacteria Escherichia coli and Pseudomonas aeruginosa, as well as fungus Candida albicans in vitro in a calcium dependent manner. However, rAalb_CTL2 could not promote type 2 dengue virus (DENV-2) replication in THP-1 and BHK-21 cell lines. These findings uncover that Aalb_CTL2 might be involved in the innate immunity of mosquito to resist microorganism multiplication in sugar and blood meals to help mosquito survive in the varied natural environment.

Functional Analysis of a CTL-X-Type Lectin CTL16 in Development and Innate Immunity of Tribolium castaneum

C-type lectins (CTLs) are a class of proteins containing carbohydrate recognition domains (CRDs), which are characteristic modules that recognize various glycoconjugates and function primarily in immunity. CTLs have been reported to affect growth and development and positively regulate innate immunity in Tribolium castaneum. However, the regulatory mechanisms of TcCTL16 proteins are still unclear. Here, spatiotemporal analyses displayed that TcCTL16 was highly expressed in late pupae and early adults. TcCTL16 RNA interference in early larvae shortened their body length and narrowed their body width, leading to the death of 98% of the larvae in the pupal stage. Further analysis found that the expression level of muscle-regulation-related genes, including cut, vestigial, erect wing, apterous, and spalt major, and muscle-composition-related genes, including Myosin heavy chain and Myosin light chain, were obviously down-regulated after TcCTL16 silencing in T. castaneum. In addition, the transcription of TcCTL16 was mainly distributed in the hemolymph. TcCTL16 was significantly upregulated after challenges with lipopolysaccharides, peptidoglycans, Escherichia coli, and Staphylococcus aureus. Recombinant CRDs of TcCTL16 bind directly to the tested bacteria (except Bacillus subtilis); they also induce extensive bacterial agglutination in the presence of Ca²⁺. On the contrary, after TcCTL16 silencing in the late larval stage, T. castaneum were able to develop normally. Moreover, the transcript levels of seven antimicrobial peptide genes (attacin2, defensins1, defensins2, coleoptericin1, coleoptericin2, cecropins2, and cecropins3) and one transcription factor gene (relish) were significantly increased under E. coli challenge and led to an increased survival rate of T. castaneum when infected with S. aureus or E. coli, suggesting that TcCTL16 deficiency could be compensated for by increasing AMP expression via the IMD pathways in T. castaneum. In conclusion, this study found that TcCTL16 could be involved in developmental regulation in early larvae and compensate for the loss of CTL function by regulating the expression of AMPs in late larvae, thus laying a solid foundation for further studies on T. castaneum CTLs.

A C-type lectin induces NLRP3 inflammasome activation via TLR4 interaction in human peripheral blood mononuclear cells

Lectins are a large group of proteins found in many snake venoms. BjcuL is a C-type lectin from Bothrops jararacussu snake venom that does not present cytotoxicity action on human peripheral blood mononuclear cells (PBMCs) at concentrations of 5 and 10 μg/mL. BjcuL demonstrates an immunomodulatory role in PBMCs with the production of pro- and anti-inflammatory cytokines (IL-2, IL-10, IFN-γ, IL-6, TNF-α, and IL-17) in addition to stimulate T cells to produce reactive oxygen species (ROS) that could play a role in the acute inflammatory reaction observed in the victims. Inflammasomes are an essential arm in cells of innate immunity to detect and sense a range of endogenous or exogenous, sterile, or infectious stimuli to elicit cellular responses and effector mechanisms. NLRP3 inflammasome is a significant target for this study, because the lectin is responsible for leukocyte activation stimulating the release of inflammatory mediators, which results in dynamic cellular responses to remove the detrimental process to the body in snakebites. Thus, this study aimed to investigate how isolated BjcuL from B. jararacussu venom affects NLRP3 inflammasome activation on PBMCs. For this, the cells were isolated by density gradient and incubated with BjcuL at different periods and concentrations for the evaluation of the activation of the NLRP3 inflammasome through gene and protein expressions of ASC, CASPASE-1, and NLRP3 by RT-qPCR, Western blot, and immunofluorescence, as well as the participation of Toll-like receptor 4 (TLR4) and ROS in the IL-1β production, a product resultant of the NLRP3 inflammasome activation. Herein, BjcuL interacts with TLR4 as demonstrated by in vitro and in silico studies and induces cytokines release via NF-κB signaling. By genic and protein expression assays, BjcuL activates NLRP3 inflammasome, and the pharmacological modulation with LPS-RS, an antagonist of TLR4; LPS-SM, an agonist of TLR4; MCC950, a specific NLRP3 inhibitor, and rotenone, an inhibitor of mitochondrial ROS, confirmed the participation of TLR4 and ROS in the NLRP3 inflammasome activation and IL-1β liberation. The effects of BjcuL on the regulation and activation of the NLRP3 inflammasome complex via TLR4 activation with ROS participation may be determinant for the development of the inflammatory local effects seen in snakebite victims. In addition, in silico together with in vitro studies provide information that may be useful in the rational design of TLR agonists as well as new adjuvants for immunomodulatory therapy.

A C-type lectin from Crassostrea gigas with novel EFG/FVN motif involved in recognition of various PAMPs and induction of interleukin expression

C-type lectins (CTLs) are a superfamily of Ca²⁺-dependent carbohydrate-recognition proteins, which participate in the nonself-recognition and triggering the transduction pathways in the innate immunity. In the present study, a novel CTL (designated as CgCLEC-TM2) with a carbohydrate-recognition domain (CRD) and a transmembrane domain (TM) was identified from the Pacific oyster Crassostrea gigas. Two novel EFG and FVN motifs were found in Ca²⁺-binding site 2 of CgCLEC-TM2. The mRNA transcripts of CgCLEC-TM2 were detected in all tested tissues with the highest expression level in haemocytes, which was 94.41-fold (p < 0.01) of that in adductor muscle. The relative expression level of CgCLEC-TM2 in haemocytes significantly up-regulated at 6 h and 24 h after the stimulation of Vibrio splendidus, which was 4.94- and 12.77-fold of that in control group (p < 0.01), respectively. The recombinant CRD of CgCLEC-TM2 (rCRD) was able to bind lipopolysaccharide (LPS), mannose (MAN), peptidoglycan (PGN), and poly (I: C) in a Ca²⁺-dependent manner. The rCRD exhibited binding activity to V. anguillarum, Bacillus subtilis, V. splendidus, Escherichia coli, Pichia pastoris, Staphylococcus aureus and Micrococcus luteus in a Ca²⁺-dependent manner. The rCRD also exhibited agglutination activity to E. coli, V. splendidus, S. aureus, M. luteus and P. pastoris in a Ca²⁺-dependent manner. The phagocytosis rate of haemocytes towards V. splendidus significantly down-regulated from 27.2% to 20.9% after treatment of anti-CgCLEC-TM2-CRD antibody, while the growth of V. splendidus and E. coli was inhibited compared with the TBS and rTrx groups. After the expression of CgCLEC-TM2 was inhibited by RNAi, the expression level of phospho-extracellular regulated protein kinases (p-CgERK) in haemocytes, and the mRNA expressions of interleukin17s (CgIL17-1 and CgIL17-4) decreased significantly after V. splendidus stimulation, compared with that in EGFP-RNAi oysters, respectively. These results suggested that CgCLEC-TM2 with novel motifs served as a pattern recognition receptor (PRR) involved in the recognition of microorganisms, and induction of CgIL17s expression in the immune response of oysters.

A unique C-type lectin, Ladderlectin, from large yellow croaker (Larimichthys crocea) is involved in bacterial cell membrane damage

Ladderlectin is unique C-type lectin because it has been so far found only in teleost fish. In this study, large yellow croaker (Larimichthys crocea) Ladderlecin (LcLL) sequence was identified and characterized. LcLL encodes a polypeptide of 186 amino acids that includes a signal peptide and a C-type lectin-like domains (CTLD) with two sugar-binding motifs of WSD and EPN. Tissues distribution analysis revealed that LcLL is a ubiquitous gene, with the highest expression in head kidney and gill. Subcellular localization showed that LcLL was in cytoplasm and nucleus of HEK 293T cells. Transcripts of LcLL were significantly up regulated after immune challenge with P. plecoglossicida. In contrast to this, a sharp down-regulation occurred after Scuticociliatida infection. Moreover, recombinant LcLL (rLcLL) was prepared and exhibited hemagglutination on L. crocea and N. albiflora erythrocytes in a Ca²⁺-dependent manner, which can be only inhibited by LPS. rLcLL showed a strong ability of binding to Gram + bacteria (M. lysodeikticus, S. aureus, B. subtilis) and Gram-bacteria (P. plecoglossicida, E. coli, V. Vulnificus, V. harveyi, V. alginolyticus, V. parahaemolyticus. A. hydrophila, and E. tarda), and could agglutinate all tested bacteria except for P. plecoglossicida. Further study showed that rLcLL promoted the gathered bacteria death through damaging cell membrane based on PI staining and SEM observation. However, rLcLL does neither kill bacteria directly nor have complement-activating activities. Altogether, these results demonstrated that LcLL played a vital role in L. crocea innate immune towards bacterial and parasitic challenge.

A novel C-type lectin for Litopenaeus vannamei involved in the innate immune response against Vibrio infection

C-type lectins (CTLs), as a member of pattern recognition receptors, play a vital role in the innate immune response of invertebrates to eliminate micro-invaders. In this study, a novel CTL of Litopenaeus vannamei, namely, LvCTL7, was successfully cloned, with an open reading frame of 501 bp and a capability to encode 166 amino acids. Blast analysis showed that the amino acid sequence similarity between LvCTL7 and MjCTL7 (Marsupenaeus japonicus) was 57.14%. LvCTL7 was mainly expressed in hepatopancreas, muscle, gill and eyestalk. Vibrio harveyi can significantly affect LvCTL7 expression level in hepatopancreases, gills, intestines and muscles (p < 0.05). LvCTL7 recombinant protein can bind to Gram-positive bacteria (Bacillus subtilis) and Gram-negative bacteria (Vibrio parahaemolyticus and V. harveyi). It can cause the agglutination of V. alginolyticus and V. harveyi, but it had no effect on Streptococcus agalactiae and B. subtilis. The expression levels of SOD, CAT, HSP 70, Toll 2, IMD and ALF genes in the challenge group added with LvCTL7 protein were more stable than those in the direct challenge group (p < 0.05). Moreover, knockdown of LvCTL7 by double-stranded RNA interference downregulated the expression levels of genes (ALF, IMD and LvCTL5) that protect against bacterial infection (p < 0.05). These results indicated that LvCTL7 had microbial agglutination and immunoregulatory activity, and it was involved in the innate immune response against Vibrio infection in L. vannamei.

Identification and analysis of C-type lectins from Helicoverpa armigera in response to the entomopathogenic fungus Metarhizium rileyi infection

C-type lectins (CTLs) function as pattern recognition receptors (PRRs) and play an important role in the innate immunity of insects. To investigate the role of CTLs in the antifungal responses, we analyzed expression profiles of 36 CTLs of Helicoverpa armigera in the tissues (hemocytes, fat bodies, and midgut) after the infection by entomopathogenic fungus Metarhizium rileyi. The expression levels of many HaCTLs were found to be up-regulated after the infection. Four recombinant HaCTLs (rHaCTL11, rHaCTL12, rHaCTL27, and rHaCTL45) were expressed and purified. Analysis of the purified rHaCTLs revealed that rHaCTLs were able to bind to conidia and hyphal bodies of M. rileyi, and the affinity of rHaCTL11 and rHaCTL27 for hyphal bodies was weaker than for conidia. All these rHaCTLs agglutinate conidia and hyphal bodies in a calcium (Ca²⁺) dependent manner. Sugar specificity assays showed that d-trehalose, mannan, β-1,3-glucan, d-galactose, glucose, d-raffinose, lipopolysaccharide, and d-xylose can inhibit the binding of HaCTLs to M. rileyi. Additionally, survival assays showed that pretreatment of fungal conidia with rHaCTL11 significantly reduced the rate of host death, and knockdown of HaCTL11 significantly increased H. armigera sensitivity to fungal infection. These results suggest that HaCTLs play significant role as PRRs in the defense of H. armigera against M. rileyi infection.

A C-type lectin TcCTL1 is required for embryogenesis in Tribolium castaneum

C-type lectin S group (CTL-S) plays a variety of roles in invertebrate including pathogen recognition and activation of immune responses. Previous studies have shown that CTL-S subfamily of Tribolium castaneum is mainly divided into two clades, of which only TcCTL1 was separately located in one clade. However, it remains unclear whether TcCTL1 occurs the differentiation of function. Therefore, the CTL-S TcCTL1 gene was cloned and characterized from T. castaneum. Functional analysis revealed that TcCTL1 could recognize and agglutinate pathogens, as well as activate immune signaling pathways to participate in immune response, which was consistent with our previously reported for TcCTL5 and TcCTL6. Differently, RNAi of TcCTL1 discovered that the egg produced by dsTcCTL1-treated adult could not hatch into larvae. Further DAPI-straining embryo indicated that the process of embryogenesis in dsTcCTL1-treated beetle was defeated, implying that TcCTL1 is required for embryogenesis in T. castaneum except for immune response. These results will aid implications for the understanding of CTL-S in invertebrate.

Immune functions of C-type lectins in medical arthropods

C-type lectins (CTLs) are a family of proteins that contain 1 or more carbohydrate-recognition domains (CRDs) and bind to a broad repertoire of ligands in the presence of calcium ions. CTLs play important roles in innate immune defenses against microorganisms by acting as pattern-recognition receptors (PRRs) for invading pathogens, such as bacteria, viruses, and parasites. After binding to pathogen-associated ligands, CTLs mediate immune responses, such as agglutination, phagocytosis, and the activation of phenol oxidase progenitors, thereby clearing pathogens. CTLs are an evolutionarily conserved family found in almost all vertebrates and invertebrates. Medical arthropods can acquire and transmit a range pathogens through various approaches, such as bloodsucking, lancing, and parasitism, thus infecting humans and animals with related diseases, some of which can be life-threatening. Recent studies have shown that lectins are important components of the arthropod immune system and are essential for the immune responses of arthropods to arthropod-borne pathogens. This article reviews the current understanding of the structure, function, and signaling pathways involved in CTLs derived from important medical arthropods.

RNAi-mediated silencing of an egg-specific gene Nllet1 results in hatch failure in the brown planthopper

BACKGROUND

The brown planthopper (BPH) is one of the most destructive agricultural pests in Asia. RNA interference (RNAi)-mediated pest management has been under development for years, and the selection of appropriate target genes is important for pest-targeted RNAi. C-type lectins (CTLs) are a class of genes that perform a variety of functions, such as the regulation of growth and development.

RESULTS

A CTL-S protein named Nllet1, containing a single calcium ion (Ca²⁺ )-dependent carbohydrate-binding domain (CRD) with a conserved triplet motif QPD was identified and functionally characterized in BPH. Expression profiles at both the transcriptional and translational levels show that Nllet1 accumulates during the serosal cuticle (SC) formation period. Immunofluorescence and immunogold labeling further demonstrated that Nllet1 is located in the serosal endocuticle (en-SC). Maternal RNAi-mediated silencing of Nllet1 disrupted the SC structure, accompanied by a loss of the outward barrier and 100% embryo mortality. Injection of 10 ng dsNllet1 or dsNllet1' per female adult BPH resulted in a total failure of egg hatching.

CONCLUSION

Nllet1 is essential for SC formation and embryonic development in BPH, which helps us understand the important roles of CTL-Ss. Additionally, BPH eggs show high sensitivity to the depletion of Nllet1. This study indicates that Nllet1 is a promising candidate gene that can be used to develop RNAi-based control strategies at the BPH egg stage, and it can also be used as a target for developing novel ovicides. © 2022 Society of Chemical Industry.

Orientia tsutsugamushi Infection Stimulates Syk-Dependent Responses and Innate Cytosolic Defenses in Macrophages

Orientia tsutsugamushi is an obligately intracellular bacterium and an etiological agent of scrub typhus. Human studies and animal models of scrub typhus have shown robust type 1-skewed proinflammatory responses during severe infection. Macrophages (MΦ) play a critical role in initiating such responses, yet mechanisms of innate recognition for O. tsutsugamushi remain unclear. In this study, we investigated whether Syk-dependent C-type lectin receptors (CLRs) contribute to innate immune recognition and the generation of proinflammatory responses. To validate the role of CLRs in scrub typhus, we infected murine bone marrow-derived MΦ with O. tsutsugamushi in the presence of selective Syk inhibitors and analyzed a panel of CLRs and proinflammatory markers via qRT-PCR. We found that Mincle/Clec4a and Clec5a transcription was significantly abrogated upon Syk inhibition at 6 h of infection. The effect of Syk inhibition on Mincle protein expression was validated via Western blot. Syk-inhibited MΦ had diminished expression of type 1 cytokines/chemokines (Il12p40, Tnf, Il27p28, Cxcl1) during infection. Additionally, expression of innate immune cytosolic sensors (Mx1 and Oas1-3) was highly induced in the brain of lethally infected mice. We established that Mx1 and Oas1 expression was reduced in Syk-inhibited MΦ, while Oas2, Oas3, and MerTK were not sensitive to Syk inhibition. This study reveals that Syk-dependent CLRs contribute to inflammatory responses against O. tsutsugamushi. It also provides the first evidence for Syk-dependent activation of intracellular defenses during infection, suggesting a role of pattern recognition receptor crosstalk in orchestrating macrophage-mediated responses to this poorly studied bacterium.

Reference Genome Sequences of the Oriental Armyworm, Mythimna separata (Lepidoptera: Noctuidae)

Lepidopteran insects are an important group of animals, including those used as biochemical and physiological model species in the insect and silk industries as well as others that are major agricultural pests. Therefore, the genome sequences of several lepidopteran insects have been reported. The oriental armyworm, Mythimna separata, is an agricultural pest commonly used to study insect immune reactions and interactions with parasitoid wasps as hosts. To improve our understanding of these research topics, reference genome sequences were constructed in the present study. Using long-read and short-read sequence data, de novo assembly and polishing were performed and haplotigs were purged. Subsequently, gene predictions and functional annotations were performed. To search for orthologs of the Toll and Immune Deficiency (IMD) pathways and for C-type lectins, annotation data analysis, BLASTp, and Hummer scans were performed. The M. separata genome is 682 Mbp; its contig N50 was 2.7 Mbp, with 21,970 genes and 24,452 coding sites predicted. All orthologs of the core components of the Toll and IMD pathways and 105 C-type lectins were identified. These results suggest that the genome data were of sufficient quality for use as reference genome data and could contribute to promoting M. separata and lepidopteran research at the molecular and genome levels.

Water-soluble trehalose glycolipids show superior Mincle binding and signaling but impaired phagocytosis and IL-1β production

The tremendous potential of trehalose glycolipids as vaccine adjuvants has incentivized the study of how the structures of these ligands relate to their Mincle-mediated agonist activities. Despite this, structure-activity work in the field has been largely empirical, and less is known about how Mincle-independent pathways might be affected by different trehalose glycolipids, and whether Mincle binding by itself can serve as a proxy for adjuvanticity. There is also much demand for more water-soluble Mincle ligands. To address this need, we prepared polyethylene glycol modified trehalose glycolipids (PEG-TGLs) with enhanced water solubility and strong murine Mincle (mMincle) binding and signaling. However, only modest cytokine and chemokine responses were observed upon the treatment of GM-CSF treated bone-marrow cells with the PEG-TGLs. Notability, no IL-1β was observed. Using RNA-Seq analysis and a representative PEG-TGL, we determined that the more water-soluble adducts were less able to activate phagocytic pathways, and hence, failed to induce IL-1β production. Taken together, our data suggests that in addition to strong Mincle binding, which is a pre-requisite for Mincle-mediated cellular responses, the physical presentation of trehalose glycolipids in colloidal form is required for inflammasome activation, and hence, a strong inflammatory immune response.

Neighboring mutation-mediated enhancement of dengue virus infectivity and spread

Frequent turnover of dengue virus (DENV) clades is one of the major forces driving DENV persistence and prevalence. In this study, we assess the fitness advantage of nine stable substitutions within the envelope (E) protein of DENV serotypes. Two tandem neighboring substitutions, threonine to lysine at the 226th (T226K) and glycine to glutamic acid at the 228th (G228E) residues in the DENV2 Asian I genotype, enhance virus infectivity in either mosquitoes or mammalian hosts, thereby promoting clades turnover and dengue epidemics. Mechanistic studies indicate that the substitution-mediated polarity changes in these two residues increase the binding affinity of E for host C-type lectins. Accordingly, we predict that a G228E substitution could potentially result in a forthcoming epidemic of the DENV2 Cosmopolitan genotype. Investigations into the substitutions associated with DENV fitness in hosts may offer mechanistic insights into dengue prevalence, thus providing a warning of potential epidemics in the future.

Identification and functional characterization of C-type lectins and crustins provide new insights into the immune response of Portunus trituberculatus

A meticulous understanding of the immune characteristics of aquaculture animals is the basis for developing precise disease prevention and control strategies. In this study, four novel C-type lectins (PtCTL-5, PtCTL-6, PtCTL-7 and PtCTL-8) including a single carbohydrate-recognition domain (CRD), and four novel crustins (Ptcrustin-1, Ptcrustin-2, Ptcrustin-3 and Ptcrustin-4) with a single whey acidic protein (WAP) domain were identified from the swimming crab Portunus trituberculatus. Tissue distribution analysis indicated that most of the target genes were predominantly expressed in the hepatopancreas in all examined tissues, except for Ptcrustin-1 which were mainly expressed in the gills. Our results showed that the eight genes displayed various transcriptional profiles across different tissues. In hemocytes, the PtCTL-7 responded quickly to Vibrio alginolyticus and exhibited much more strongly up-regulation than other three PtCTLs. The Ptcrustin-1 rapidly responded to V. alginolyticus within 3 h in all the three tested tissues. Furthermore, recombinant proteins of PtCTL-5 and PtCTL-8 were successfully obtained, and both of them displayed bacterial binding activities toward V. alginolyticus, V. harveyi and Staphylococcus aureus, and only showed antibacterial activity against V. harveyi. These findings provided new insights into the diverse immune response of P. trituberculatus and laid theoretical foundations for the development of precise disease prevention and control strategies in P. trituberculatus farming. Moreover, the specific anti-V. harveyi activities exhibited by rPtCTL-5 and rPtCTL-8 suggested their promising application prospects for controlling diseases caused by V. harveyi.

Immulectin-2 from the ghost moth, Thitarodes xiaojinensis (Lepidoptera: Hepialidae), modulates cellular and humoral responses against fungal infection

C type-lectins constitute a large family of pattern recognition receptors, playing important roles in insect immune defenses. Thitarodes xiaojinensis larvae showed distinct immune features after Ophiocordyceps sinensis, Cordyceps militaris, or Beauveria bassiana infection. Based on transcriptome and immunoblot analysis, we found that immulectin-2 (IML2) was induced after T. xiaojinensis larvae were infected by C. militaris or B. bassiana but maintained at a low level after larvae injected with O. sinensis or Ringer's buffer. Recombinant IML2 (rIML2) could promote melanization, encapsulation, phagocytosis, and hemocyte aggregation in vitro. RNA interference with IML2 induced a significant reduction in the transcript levels of various antimicrobial peptides. Importantly, we found that the abundance of O. sinensis blastospores coated with rIML2 dramatically decreased in the host hemolymph. Overall, this study demonstrated that T. xiaojinensis IML2 modulates cellular and humoral responses to entomopathogenic fungi, broadening our view of the immune interaction between O. sinensis and its host.

A C-type lectin containing two carbohydrate recognition domains participates in the antibacterial response by regulating the JNK pathway and promoting phagocytosis

C-type lectins (CTLs) are important immune-related molecules in crustaceans. However, the immunologic mechanism by which CTLs eliminate invading pathogens is still unclear. In this study, we studied the antimicrobial mechanism of a CTL containing two carbohydrate recognition domains (DClec). After Aeromonas hydrophila challenge, several antimicrobial peptides (ALF1, ALF4, ALF5 and lys-i2) were upregulated. The transcript levels of ALF1, ALF4 and ALF5 were downregulated after A. hydrophila challenge in groups with DClec interference or inhibition compared with the control group. Similar results were obtained after c-Jun N-terminal kinase (JNK) interference. This finding indicates that DClec might regulate the JNK signalling pathway and subsequently adjust antimicrobial peptide (AMP) expression. Additionally, we found that DClec was secreted into the hemolymph. Recombinant protein DClec (rDClec) agglutinated gram-positive or gram-negative bacteria. Both rDClec and the native DClec in hemolymph bound to different bacteria. In this process, Ca²⁺ promoted the rDClec bacterial binding ability. After DClec interference, the phagocytosis ability of hemocytes was lower than that of the control group. Therefore, DClec can facilitate bacterial elimination by promoting AMPs expression and hemocyte phagocytosis.

mori Nucleopolyhedrovirus (BmNPV) through Involvement in Apoptosis

C-type lectins (CTLs) are widely distributed in mammals, insects, and plants, which act as pattern recognition receptors (PRRs) to recognize pathogens and initiate immune responses. In this study, we identified a C-type lectin gene called BmIML-2 from the silkworm Bombyx mori. Its open reading frame (ORF) encodes 314 amino acids, which contain dual tandem C-type lectin-like domain (CTLD). BmIML-2 is highly expressed in the fat body and is significantly induced at 24 h after BmNPV infection. Moreover, overexpression of BmIML-2 dramatically inhibited the proliferation of BmNPV, and knockdown assay via siRNA further validated the inhibition of BmIML-2 on viral proliferation. In addition, transcript level detection of apoptosis-related genes and observation of apoptosis bodies implied that overexpression of BmIML-2 promoted BmNPV-induced apoptosis. Immunofluorescence analysis indicated that BmIML-2 distributed throughout the cytoplasm and was slightly concentrated in the cell membrane. Taken together, our results suggest that BmIML-2 could inhibit in the proliferation of BmNPV by facilitating cell apoptosis.

Divergent Specialization of Simple Venom Gene Profiles among Rear-Fanged Snake Genera (Helicops and Leptodeira, Dipsadinae, Colubridae)

Many venomous animals express toxins that show extraordinary levels of variation both within and among species. In snakes, most studies of venom variation focus on front-fanged species in the families Viperidae and Elapidae, even though rear-fanged snakes in other families vary along the same ecological axes important to venom evolution. Here we characterized venom gland transcriptomes from 19 snakes across two dipsadine rear-fanged genera (Leptodeira and Helicops, Colubridae) and two front-fanged genera (Bothrops, Viperidae; Micrurus, Elapidae). We compared patterns of composition, variation, and diversity in venom transcripts within and among all four genera. Venom gland transcriptomes of rear-fanged Helicops and Leptodeira and front-fanged Micrurus are each dominated by expression of single toxin families (C-type lectins, snake venom metalloproteinase, and phospholipase A2, respectively), unlike highly diverse front-fanged Bothrops venoms. In addition, expression patterns of congeners are much more similar to each other than they are to species from other genera. These results illustrate the repeatability of simple venom profiles in rear-fanged snakes and the potential for relatively constrained venom composition within genera.

The Dual Functions of a Bracovirus C-Type Lectin in Caterpillar Immune Response Manipulation

Parasitoids are widespread in natural ecosystems and normally equipped with diverse viral factors to defeat host immune responses. On the other hand, parasitoids can enhance the antibacterial abilities and improve the hypoimmunity traits of parasitized hosts that may encounter pathogenic infections. These adaptive strategies guarantee the survival of parasitoid offspring, yet their underlying mechanisms are poorly understood. Here, we focused on Cotesia vestalis, an endoparasitoid of the diamondback moth Plutella xylostella, and found that C. vestalis parasitization decreases the number of host hemocytes, leading to disruption of the encapsulation reaction. We further found that one bracovirus C-type lectin gene, CvBV_28-1, is highly expressed in the hemocytes of parasitized hosts and participates in suppressing the proliferation rate of host hemocytes, which in turn reduces their population and represses the process of encapsulation. Moreover, CvBV_28-1 presents a classical bacterial clearance ability via the agglutination response in a Ca²⁺-dependent manner in response to gram-positive bacteria. Our study provides insights into the innovative strategy of a parasitoid-derived viral gene that has dual functions to manipulate host immunity for a successful parasitism.

A single-CRD C-type lectin from Haliotis discus hannai acts as pattern recognition receptor enhancing hemocytes opsonization

C-type lectins (CTLs), as a member of the Ca²⁺-dependent carbohydrate recognition protein superfamily, play multiple roles in non-self recognition and the elimination of invading pathogens. In this study, a C-type lectin was identified and characterized from the Pacific abalone Haliotis discus hannai (designed as HdClec), and its open reading frame (ORF) encoded a polypeptide of 163 amino acids containing a typical signal peptide and only one carbohydrate-recognition domain (CRD). The deduced amino acid sequence of CRD in HdClec shared identities ranging from 22.4% to 39.8% with that of other identified CRDs of CTLs. A novel NPN motif was found in Ca²⁺-binding site 2 of HdClec. The mRNA transcripts of HdClec were detectable in all the examined tissues of non-stimulated abalones, with the highest expression in hepatopancreas (224.13-fold of that in gills). The expression of HdClec mRNA in hemocytes was significantly up-regulated after Vibrio harveyi challenge. Recombinant HdClec protein (rHdClec) could bind lipopolysaccharide (LPS) and peptidoglycan (PGN) in vitro in the presence of Ca²⁺. Coinciding with the PAMPs binding assay, rHdClec displayed broad agglutination activities towards Gram-negative bacteria V. splendidus, V. anguillarum, V. parahaemolyticus, V. harveyi, Escherichia coli, and Gram-positive bacteria Micrococcus luteus. Moreover, rHdClec could significantly elicit the chemotactic response of hemocytes in vitro. And the phagocytosis and encapsulation ability of hemocytes could be significantly enhanced by rHdClec. All these results showed that HdClec could function as pattern recognition receptors (PRRs) and further enhance the opsonization of hemocytes, which might play a crucial role in the innate immune responses of Pacific abalone.

Crucial roles of a novel exoskeletal-derived lectin in innate immunity of the oriental river prawn, Macrobrachium nipponense

As important pattern recognition receptors (PRRs), C-type lectins play crucial roles in the crustacean innate immune system. In this study, a novel C-type lectin, designated as MnLec1, was obtained from the exoskeleton of the oriental river prawn Macrobrachium nipponense for the first time. The full-length cDNA of MnLec1 was 1329 bp with an open reading frame of 774 bp. The predicted MnLec1 protein contains a single carbohydrate-recognition domain with an EPN/LND motif and one Ca²⁺ binding site-2. MnLec1 transcripts were widely detected in the tested tissues of M. nipponense and significantly up-regulated after Aeromonas hydrophila challenge. The recombinant MnLec1 protein was found to have a wide spectrum of binding activities towards various microorganisms, agglutinate two kinds of Gram-negative bacteria (Escherichia coli and A. hydrophila) in a Ca²⁺ -independent manner. What's more, the survivability of prawns was significantly down-regulated after RNAi of MnLec1 when infected with A. hydrophila. Collectively, these findings suggest that MnLec1 from the exoskeleton might function as a PRR and play a crucial role in immune defense against invading pathogens in M. nipponense.

Genome-wide identification of endosialin family of C-type lectins in common carp (Cyprinus carpio) and their response following Aeromonas hydrophila infection

The endosialin family is the group XIV of C-type lectin, regulating several processes involved in innate immunity and inflammation. Endosialin family genes have been extensively studied in human and mammals, however, rarely reported in teleost. In the present study, a set of 8 endosialin family genes was identified across the entire common carp genome. Functional domain and motif prediction and phylogenetic analysis supported their annotation and orthologies. Through examining gene copy number across several vertebrates, endosialin family genes were found have undergone gene duplication. Most of the endosialin family genes were ubiquitously expressed during common carp early developmental stages, and presented tissue-specific expression patterns in various healthy tissues, with relatively high expression in intestine, liver, gill, spleen and kidney, indicating their likely essential roles in maintaining homeostasis and host immune response. After Aeromonas hydrophila infection, gene thbd-1, thbd-2 and cd93-2 were significantly up-regulated at one or more timepoints in spleen and kidney, while gene cd248a-1, cd248a-2, cd248b-1, cd248b-2, and cd93-1 were significantly down-regulated. Taken together, all these results suggested that endosialin family genes were involved in host immune response to A. hydrophila infection in common carp, and provided fundamental genomic resources for better understanding the critical roles of endosialin family on the primary innate immune processes in teleost.

C-type lectin-(like) fold - Protein-protein interaction patterns and utilization

The C-type lectin-like fold (CTL fold) is a building block of many proteins, including saccharide-binding lectins, natural killer cell receptors, macrophage mannose receptor, selectins, collectins, snake venoms and others. Some are important players in innate immunity and are involved in the first-line response to virally infected cells or cancer cells, some play a role in antimicrobial defense, and some are potential targets for fight against problems connected with allergies, obesity, and autoimmunity. The structure of a CTL domain typically contains two α-helices, two small β-sheets and a long surface loop, with two or three disulfide bridges stabilizing the structure. This small domain is often involved in interactions with a target molecule, however, utilizing varied parts of the domain surface, with or without structural modifications. More than 500 three-dimensional structures of CTL fold-containing proteins are available in the Protein Data Bank, including a significant number of complexes with their key interacting partners (protein:protein complexes). The amount of available structural data enables a detailed analysis of the rules of interaction patterns utilized in activation, inhibition, attachment and other pathways or functionalities. Interpretation of known CTL receptor structures and all other CTL-containing proteins and complexes with described three-dimensional structures, complemented with sequence/structure/interaction correlation analysis offers a comprehensive view of the rules of interaction patterns of the CTL fold. The results are of value for prediction of interaction behavior of so far not understood CTL-containing proteins and development of new protein binders based on this fold, with applications in biomedicine or biotechnologies. It follows from the available structural data that almost the whole surface of the CTL fold is utilized in protein:protein interactions, with the heaviest frequency of utilization in the canonical interaction region. The individual categories of interactions differ in the interface buildup strategy. The strongest CTL binders rely on interfaces with large interaction area, presence of hydrophobic core, or high surface complementarity. The typical interaction surfaces of the fold are not conserved in amino acid sequence and can be utilized in design of new binders for biotechnological applications.

Functional analysis of TcCTL12 in innate immunity and development in Tribolium castaneum

C-type lectins (CTLs) play vital roles in invertebrates' innate immunity. Six CTL-X type lectins are identified in Tribolium castaneum. However, their functions and regulating mechanisms remain elusive. Here, TcCTL12, one CTL-X, was identified and cloned from T. castaneum. Spatiotemporal expression profiling revealed that TcCTL12 highly expressed in late pupa and early adult of T. castaneum in comparison with other developmental stages, and exhibited the highest expression level in the haemolymph and central nervous system (CNS). Then, the expression of TcCTL12 was remarkably induced by the stimulation of Escherichia coli and Staphylococcus aureus. Moreover, the recombinant protein TcCTL12 could bind pathogen-associated molecular patterns (PAMPs) including LPS and PGN, and displayed agglutinative activity to both Gram-positive and Gram-negative bacteria in a calcium-dependent manner in vitro. Furthermore, RNAi of TcCTL12 caused T. castaneum pupation and eclosion defected. The abnormal pupa thinned their epidermal, and appeared the abnormal development of muscle cell compared with the control group. Additionally, depletion of TcCTL12 resulted in reducing fertility of offspring and affected their fecundity. In sum, these results indicated that TcCTL12 had extensive functions in the regulation of development in T. castaneum, in addition to the immune response. It further expanded insights into CTL functions in insects.

CTL10 has multiple functions in the innate immune responses of the silkworm, Bombyx mori

Insect C-type lectins (CTLs) play crucial roles in modulating the humoral and cellular immune responses. In the domesticated silkworm Bombyx mori L., BmCTL10 gene encodes an immulectin containing two carbohydrate recognition domains (CRDs). The phylogenetic analysis showed that BmCTL10 didn't cluster with other immulectin homologs in B. mori. BmCTL10 was mainly expressed in second to fifth instar larvae, wandering stage larvae, prepupa, and adults. In naïve fifth instar larvae, BmCTL10 was predominantly expressed in the fat body and epidermis. In second instar larvae, the topical application of Beauveria bassiana by immersion caused down-regulation of BmCTL10. The intra-hemocoel injection of E. coli, S. aureus, B. bassiana, and 20-hydroxyecdysone in fifth instar larvae caused tissue and time-specific inductions. The recombinant protein (rBmCTL10) can bind to larval hemocytes and various pathogen-associated molecular patterns to enhance hemocyte-mediated nodulation, phagocytosis, and encapsulation. rBmCTL10 caused significant upregulation of most antimicrobial peptides and nitric oxide synthase 1 in hemocytes in vivo. Yeast two-hybrid demonstrated that integrin β3 and β4 subunits can interact with BmCTL10. Furthermore, only CRD2 can interact with the β3, while both CRD1 and CRD2 can interact with the β4. Taken together, this study showed that BmCTL10 has multiple functions in the innate immune responses of B. mori and two integrin β subunits are their potential receptors.

Identifying and antagonizing the interactions between layilin and glycosylated collagens

Layilin is a small type I transmembrane receptor thought to bridge extracellular ligands with the cytoskeleton through its intracellular interactions with the scaffolding protein talin. Recent bulk- and single-cell RNA sequencing experiments have repeatedly found layilin to be highly upregulated in key T cell sub-populations in multiple disease states, suggesting its importance to the adaptive immune response. Despite this prevalence, little is known about layilin's precise role in mediating extracellular interactions or how these interactions can be modulated in disease states. Here we take advantage of layilin's dependence on calcium ions to discover its interactions with highly glycosylated type II, IV, V, and VI collagens. Toward exploring layilin's role in disease, we exploited the Ca²⁺ dependence in a differential phage display strategy to engineer species cross-reactive antibodies that block this interaction.

Characterization of a C-Type Lectin Domain-Containing Protein with Antibacterial Activity from Pacific Abalone (Haliotis discus hannai)

Genes that influence the growth of Pacific abalone (Haliotis discus hannai) may improve the productivity of the aquaculture industry. Previous research demonstrated that the differential expression of a gene encoding a C-type lectin domain-containing protein (CTLD) was associated with a faster growth in Pacific abalone. We analyzed this gene and identified an open reading frame that consisted of 145 amino acids. The sequence showed a significant homology to other genes that encode CTLDs in the genus Haliotis. Expression profiling analysis at different developmental stages and from various tissues showed that the gene was first expressed at approximately 50 days after fertilization (shell length of 2.47 ± 0.13 mm). In adult Pacific abalone, the gene was strongly expressed in the epipodium, gill, and mantle. Recombinant Pacific abalone CTLD purified from Escherichia coli exhibited antimicrobial activity against several Gram-positive bacteria (Bacillus subtilis, Streptococcus iniae, and Lactococcus garvieae) and Gram-negative bacteria (Vibrio alginolyticus and Vibrio harveyi). We also performed bacterial agglutination assays in the presence of Ca²⁺, as well as bacterial binding assays in the presence of the detergent dodecyl maltoside. Incubation with E. coli and B. subtilis cells suggested that the CTLD stimulated Ca²⁺-dependent bacterial agglutination. Our results suggest that this novel Pacific abalone CTLD is important for the pathogen recognition in the gastropod host defense mechanism.

Targeting Tn-Antigen-Positive Human Tumors with a Recombinant Human Macrophage Galactose C-Type Lectin

Alterations in glycosylation cause the emergence of tumor-associated carbohydrate antigens (TACAs) during tumorigenesis. Truncation of O-glycans reveals the Thomsen nouveau (Tn) antigen, an N-acetylgalactosamine (GalNAc) frequently attached to serine or threonine amino acids, that is accessible on the surface of cancer cells but not on healthy cells. Interestingly, GalNac can be recognized by macrophage galactose lectin (MGL), a type C lectin receptor expressed in immune cells. In this study, recombinant MGL fragments were tested in vitro for their cancer cell-targeting efficiency by flow cytometry and confocal microscopy and in vivo after administration of fluorescent MGL to tumor-bearing mice. Our results demonstrate the ability of MGL to target Tn-positive human tumors without inducing toxicity. This outcome makes MGL, a fragment of a normal human protein, the first vector candidate for in vivo diagnosis and imaging of human tumors and, possibly, for therapeutic applications.

Expression and functional characterization of the mannose receptor (MR) from Nile tilapia (Oreochromis niloticus) in response to bacterial infection

Mannose receptor (MR) as a member of the pattern recognition receptors (PRRs) plays an important role in the immune response. In mammals, the role of MR in the regulation of phagocytosis is clarified; however, its contribution to opsonize phagocytosis remains unclear in bony fish. In this study, the expression pattern of Nile tilapia mannose receptor gene (OnMR) was investigated and its regulation of the phagocytosis of monocytes/macrophages to pathogenic bacteria was identified. The full-length of OnMR open reading frame is 4314 bp, encoding a peptide containing 1437 amino acid residues. The deduced amino acid sequence revealed that OnMR contained a cysteine-rich domain, a fibronectin type II domain, multiple C-type lectin-like domains, a transmembrane domain and a short cytoplasmic domain. Tissue distribution analysis showed the OnMR transcripts was widely distribute in the ten detected tissues, and highly expressed in head kidney, hind kidney, intestine and spleen. After S. agalactiae and A. hydrophila infection, the expression of OnMR in head kidney and spleen increased significantly. Moreover, the expression of OnMR in MO/Mø were also upregulated post the infection of bacteria and mannose solutions in vitro. This suggested that MR, as a mannose receptor on macrophage surface, could respond strongly to the stimulation of pathogenic bacteria. In addition, the (r)OnMR protein could effectively bind and agglutinate S. agalactiae and A. hydrophila, and regulate the phagocytic ability of monocytes/macrophages to pathogenic bacteria. These results suggest that OnMR is involved in response against bacterial infection in Nile tilapia, and this study will help us better understand the function of MR in teleost fish.