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Lectins are important pattern recognition receptors (PRRs) and their immunological action is related to the recognition of glycans present in the pathogen cells surface. The lectins described for Litopenaeus vannamei are divided into C-type, L-type and galectin, which are mainly expressed in hepatopancreas and hemocytes. They are involved in several immune response pathways, such as phagocytosis, hemocytes recruitment, prophenoloxidase activation, and gene regulation. Although lectins have multiple immune functions, most experimental challenges focus only on WSSV and Vibrio sp. This article is a detailed review on the role of lectins in L. vannamei immune system, bringing together information on molecular structure, temporal and special expression and immune function, highlighting the wide participation of these molecules in shrimp innate immune system. • All known Litopenaeus vannamei lectins can be classified into three categories. • L. vannamei lectins are mainly expressed in hepatopancreas, gills and hemolymph. • Many L. vannamei lectins are upregulated after pathogen challenges. • L. vannamei lectins are involved in several immune pathways. • L. vannamei lectins are involved in response against bacteria and viruses. [ABSTRACT FROM AUTHOR]

C-type lectins (CTLs) are glycan-binding pattern recognition receptors (PRRs) that can bind to carbohydrates on pathogen surfaces, triggering immune responses in shrimp innate immunity. In this study, a unique Ca2+-inhibited CTL named Fc Lec was identified and characterized in Chinese shrimp Fenneropenaeus chinensis. The full-length cDNA sequence of Fc Lec was 976 bp (GenBank accession number KU361826), with a 615 bp open reading frame (ORF) encoding 204 amino acids. Fc Lec possesses a C-type lectin-like domain (CTLD) containing four conserved cysteines (Cys105, Cys174, Cys192, and Cys200) and two sugar-binding site structures (QPD and LNP). The tertiary structure of Fc Lec deduced revealed three α-helices and eight β-pleated sheets. The mRNA expression levels of Fc Lec in hemocytes and the hepatopancreas were markedly elevated after stimulation with Vibrio anguillarum and white spot syndrome virus (WSSV). The recombinant Fc Lec protein exhibited Ca2+-independent hemagglutination and bacterial agglutination, but these activities were observed only in the presence of EDTA to chelate metal ions. These findings suggest that Fc Lec plays important and functionally distinct roles in the shrimp's innate immune response to bacteria and viruses, enriching the current understanding of the relationship between CTL activity and Ca2+ in invertebrates. [Display omitted] • A novel CTL, Fc Lec, were identified from F. chinensis. • Fc Lec plays distinct and significant roles in the innate immune system's reaction to microbial assaults. • Fc Lec exhibits Ca2+-independent and even Ca2+-inhibited activity. [ABSTRACT FROM AUTHOR]

As an important pattern recognition receptor (PRR) in the innate immune system, C-type lectin plays an important role in the innate immune process of invertebrates. Two C-type lectins SpCTL-C and SpCTL-D were characterized from mud crab (Scylla paramamosain). The predicted SpCTL-C and SpCTL-D proteins both contain a single carbohydrate-recognition domain (CRD) with key motif Gln-Pro-Ala (QPA) and Met-Pro-Ala (MPA), respectively. SpCTL-C and SpCTL-D transcripts distributed in all examined tissues, and the expression level was the highest in hepatopancreas. As PRR, the purified recombinant proteins rSpCTL-C and rSpCTL-D have high affinity for three kinds of pathogen-associated molecular patterns (PAMPs): β-glucan, lipopolysaccharide, and peptidoglycan. Besides, rSpCTL-D can bind to all nine microorganisms tested, while rSpCTL-C can bind to seven microorganisms except for Staphylococcus aureus and Micrococcus luteus. Both rSpCTL-C and rSpCTL-D showed agglutination activity towards fungi Pichia pastoris and Saccharomyces cerevisiae. However, rSpCTL-C and rSpCTL-D exhibited different antimicrobial activities: rSpCTL-D has a certain inhibitory effect on the growth of Vibrio fluvialis and M. luteus, while rSpCTL-C has no obvious inhibitory activity. The results show that rSpCTL-C and rSpCTL-D had better phagocytosis-promoting effect on M. luteus than the negative control. Meanwhile, both rSpCTL-C and rSpCTL-D had certain encapsulation-promoting activity. Collectively, two C-type lectins with novel key motifs make an important impact as PRR in immune response towards pathogens. At the same time, they play different functions in the innate immunity of mud crab S. paramamosain. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

C-type lectins (CTL) are a large group of pattern-recognition proteins and to play important roles in glycoprotein metabolism, multicellular integration, and immunity. Based on their overall domain structure, they can be classified as different groups that possess different physiological functions. A typical C-type lectin (named as Om Lec1) was identified from the fish, Onychostoma macrolepis , an important cultured fish in China. Open reading frame of Om Lec1 contains a 570 bp, encoding a protein of 189 amino acids that includes a signal peptide and a single carbohydrate-recognition domain. The phylogenetic analysis showed that Om Lec1 could be grouped with C-type lectin from other fish. Om Lec1 was expressed in all the tissues in our study, and the expression level was highest in liver. And its relative expression levels were significantly upregulated following infection with Aeromonas hydrophila. The recombinant Om Lec1 protein (r Om Lec1) could agglutinate some Gram-negative bacteria and Gram-positive bacteria in vitro in the presence of Ca2+, showing a typical Ca2+-dependent carbohydrate-binding protein. Furthermore, r Om Lec1 purified from E. coli BL21 (DE3), strongly bound to LPS and PGN, as well as all tested bacteria in a Ca2+-dependent manner. These results indicate that Om Lec1 plays a central role in the innate immune response and as a pattern recognition receptor that recognizes diverse pathogens among O. macrolepis. • A typical C-type lectin with a EPN/WND motif (Om Lec1) was identified and characterized from Onychostoma macrolepis. • The expression levels of Om Lec1 gene were significantly up-regulated after pathogen challenge. • Recombinant Om Lec1 can agglutinates various bacteria in vitro in the presence of Ca2+. • Recombinant Om Lec1 could bind some saccharides such as d -mannose, LPS and PGN. [ABSTRACT FROM AUTHOR]

• A novel C-type lectin with a EPN/WND motif (OmCTL) was identified and characterized from Onychostoma macrolepis. • The expression levels of OmCTL gene were significantly upregulated after pathogen challenge. • Recombinant OmCTL can agglutinates various bacteria in vitro in the presence of Ca2+. • Recombinant OmCTL could bind some saccharides such as d-mannose, LPS and PGN and so on. C-type lectins (CTLs) are calcium-dependent carbohydrate-binding proteins that mainly bind to carbohydrate-based or other ligands to mediate cell adhesion, recognize pathogens, and play important roles in the immune system. In the present study, a novel C-type lectin (OmCTL) isolated from Onychostoma macrolepis was investigated. The open reading frame of OmCTL comprises 468 bp, encoding a 155 amino acid polypeptide with an 18 amino acid putative signaling peptide. The predicted primary OmCTL structure contains a signal peptide, a single carbohydrate recognition domain (CRD) and an EPN/WND motif required for carbohydrate-binding specificity. Using tissue expression pattern analysis, OmCTL has been shownto be highly expressed in the liver, and is also detected in other tissues. OmCTL was significantly upregulated in the liver and spleen following infection with Aeromonas hydrophila , suggesting its involvement in immune response. The recombinant OmCTL protein (rOmCTL) agglutinated two gram-negative bacteria, Escherichia coli and A. hydrophila , in vitro in the presence of Ca2+, showing that it is a typical Ca2+-dependent carbohydrate-binding protein.Furthermore, rOmCTL purified from E. coli BL21 (DE3) strongly bound to LPS and PGN, as well as all tested bacteria in a Ca2+-independent manner. These results indicate that OmCTL plays a central role in the innate immune response and as a pattern recognition receptor that recognizes diverse pathogens among O. macrolepis. [ABSTRACT FROM AUTHOR]

Galectins, as members of lectin families, exhibit a high affinity for β-galactosides and play diverse roles in biological processes. They function as pattern recognition receptors (PRRs) with important roles in immune defense. In this study, galectin-1, designated as SpGal-1, was identified and characterized from silver pomfret (Pampus argenteus). The SpGal-1 comprises an open reading frame (ORF) spanning 396 base pairs (bp) and encodes a deduced amino acid (aa) sequence containing a single carbohydrate recognition domain (CRD). Sublocalization analysis revealed that SpGal-1 was mainly expressed in the cytoplasm. The mRNA transcripts of SpGal-1 were ubiquitously detected in various tissues, with a higher expression level in the intestine. In addition, when exposed to Photobacterium damselae subsp. damselae (PDD) infection, both the liver and head kidney exhibited significantly increased SpGal-1 mRNA expression. The recombinant protein of SpGal-1 (named as rSpGal-1) demonstrated hemagglutination against red blood cells (RBCs) from Larimichthys crocea and P. argenteus in a Ca2+ or β-Mercaptoethanol (β-ME)-independent manner. Notably, rSpGal-1 could bind with various pathogen-associated molecular patterns (PAMPs) including D-galactose, D-mannose, lipopolysaccharide (LPS), and peptidoglycan (PGN), with highest affinity to PGN. Moreover, rSpGal-1 effectively interacted with an array of bacterial types encompassing Gram-positive bacteria (Staphylococcus aureus and Nocardia seriolae) and Gram-negative bacteria (PDD and Escherichia coli, among others), with the most robust binding affinity towards PDD. Collectively, these findings highlight that SpGal-1 is a crucial PRR with involvement in the host immune defense of silver pomfret. • Galectin-1, designated as SpGal-1, was identified and characterized from Pampus argenteus. • The rSpGal-1 demonstrated hemagglutination against RBCs from Larimichthys crocea and P. argenteus. • The rSpGal-1 could bind with various pathogen-associated molecular patterns (PAMPs) and an array of bacterial types. [ABSTRACT FROM AUTHOR]

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 Tg CTL-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 Tg CTL-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 Tg CTL-1 (r Tg CTL-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 r Tg CTL-1. In general, our results showed that Tg CTL-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. • A novel C-type lectin, TgCTL-1 , was identified in blood clam, T. granosa. • TgCTL- 1 has a single carbohydrate-recognition domain (CRD) containing QPN/WDD motifs. • Expression of TgCTL-1 was rapidly and markedly up-regulated upon pathogen challenge. • The r Tg CTL-1 exhibited binding and agglutinating activities in a Ca+-dependent manner. • r Tg CTL-1 was shown to promote phagocytic activity of hemocytes especially with Ca2+. [ABSTRACT FROM AUTHOR]

C‐type lectins are carbohydrate‐binding proteins that play important roles in immunity by serving as pattern recognition receptors. In the present study, a novel nattectin‐like C‐type lectin was obtained from the weather loach, Misgurnus anguillicaudatus, designated as MaCTL. MaCTL encodes a peptide with 165 amino acids, with a signal peptide and a single C‐type lectin domain (CTLD), containing a galactose‐specific QPD motif and a conserved Ca2+‐binding site. Transcripts of MaCTL were significantly upregulated after immune challenge with its pathogen A. hydrophila. In vitro assays with recombinant MaCTL protein revealed that it exhibited hemagglutinating and bacterial agglutinating activities, in a Ca2+‐dependent manner. MaCTL was found to bind to a wide range of bacteria, as well as bind to bacterial polysaccharides LPS and PGN. Moreover, MaCTL displayed antimicrobial activity by inhibiting the growth of bacteria. These results collectively suggest that MaCTL is involved in the antibacterial defence of weather loach. [ABSTRACT FROM AUTHOR]

As pattern recognition receptors (PRRs), C-type lectins (CTLs) have important roles in the recognition and clearance of pathogens by the innate immune system. In the present study, the first Cherax quadricarinatus CTL gene (designated CqCTL) was cloned and characterized. The complete cDNA sequence of CqCTL contained an open reading frame (ORF) of 543 bp, which encoded a protein of 180 amino acids. A carbohydrate recognition domain (CRD) containing four conserved cysteines (Cys48, Cys59, Cys76, Cys177) and the EPD (Glu80-Pro81-Asn82) and QPD (Gln146-Pro147-Asn148) motifs were identified in the deduced amino acid sequence of CqCTL. The deduced tertiary structure of CqCTL revealed two α helices, five β sheets and two disulfide bonds. CqCTL exhibited high similarity with previously identified CTLs from other species. The mRNA transcripts of CqCTL were ubiquitously detectable in all the tested tissues, with the highest expression level in hepatopancreas. These results provide useful information on the potential role of CqCTL in the innate immune system of C. quadricarinatus, and lay the foundation for further studies on the CTLs of crustacean. [ABSTRACT FROM AUTHOR]

Galectins are a family of β -galactoside-binding lectins that play key roles in the invertebrate innate immunity system, but no galectin genes have been identified in the mud crab (Scylla paramamosain) so far. The present study is the first to clone a galectin gene (SpGal) from S. paramamosain , by the rapid amplification of cDNA ends technique based on expressed sequence tags. The full-length cDNA of SpGal was 3142 bp. Its open reading frame encoded a polypeptide of 280 amino acids containing a GLECT/Gal-bind lectin domain and a potential N-glycosylation site. The deduced amino acid sequence and multi-domain organization of SpGal were highly similar to those of invertebrate galectins, and phylogenetic analysis showed that SpGal was closely related to galectin isolated from Portunus trituberculatus. The mRNA transcripts of SpGal were found to be constitutively expressed in a wide range of tissues, with its expression level being higher in the hepatopancreas, gill, and hemocytes. The mRNA expression level of SpGal increased rapidly after the crabs were stimulated by Vibrio alginolyticus , and the maximum expression appeared at 6 h after the challenge. The lipopolysaccharide-binding ability of SpGal was dependent on its concentration, and it also exhibited agglutination activity with three Gram-negative (Aeromonas hydrophila , Chryseobacterium indologenes and Vibrio alginolyticus) and three Gram-positive (Bacillus aquimaris , Staphylococcus aureus and Micrococcus lysodeik) bacterial strains. In addition, hemagglutination activity with rabbit erythrocytes was observed in the absence of d -galactose. These results indicate that SpGal in S. paramamosain acts as a pattern recognition receptor to recognize a broad spectrum of microbes. The findings together indicate that SpGal plays an important role in the innate immune mechanisms of S. paramamosain against pathogenic infection. • A novel galectin in Scylla paramamosain (SpGal) was identified and characterized. • SpGal showed high sequence similarity to other crustacean galectins. • SpGal exhibited high hemagglutination activity and LPS-binding ability. • SpGal exhibited broad-spectrum bacterial agglutination activity. • SpGal may play an important role in innate immunity in S. paramamosain. [ABSTRACT FROM AUTHOR]

Plant pattern recognition receptors (PRRs) perceive pathogen‐associated molecular patterns (PAMPs) to activate immune responses. Medium‐chain 3‐hydroxy fatty acids (mc‐3‐OH‐FAs), which are widely present in Gram‐negative bacteria, were recently shown to be novel PAMPs in Arabidopsis thaliana. The Arabidopsis PRR LIPOOLIGOSACCHARIDE‐SPECIFIC REDUCED ELICITATION (LORE) is a G‐type lectin receptor‐like kinase that recognizes mc‐3‐OH‐FAs and subsequently mounts an immune response; however, the mechanisms underlying LORE activation and downstream signaling are unexplored. Here, we report that one of the mc‐3‐OH‐FAs, 3‐OH‐C10:0, induces phosphorylation of LORE at tyrosine residue 600 (Y600). Phosphorylated LORE subsequently trans‐phosphorylates the receptor‐like cytoplasmic kinase PBL34 and its close paralogs, PBL35 and PBL36, and therefore activates plant immunity. Phosphorylation of LORE Y600 is required for downstream phosphorylation of PBL34, PBL35, and PBL36. However, the Pseudomonas syringae effector HopAO1 targets LORE, dephosphorylating the tyrosine‐phosphorylated Y600 and therefore suppressing the immune response. These observations uncover the mechanism by which LORE mediates signaling in response to 3‐OH‐C10:0 in Arabidopsis. Synopsis: The Arabidopsis lectin receptor‐like kinase LORE serves as pattern‐recognition receptor for bacterial fatty acid metabolites. Here, LORE‐mediated activation of plant immune responses is shown to be mediated by LORE auto‐phosphorylation and activation of novel receptor‐like cytoplasmic kinases. LORE exhibits tyrosine kinase activity.Bacterial fatty acid metabolite 3‐OH‐C10:0 activates LORE via its phosphorylation on Tyr600.LORE phosphorylates receptor‐like cytoplasmic kinases PBL34/PBL35/PBL36 to activate immune responses.Bacterial pathogen P. syringae inhibits LORE via the secreted tyrosine phosphatase HopAO1. [ABSTRACT FROM AUTHOR]

C-type lectins (CTLs) have characteristic carbohydrate recognition domains (CRDs) and play important roles in the immune system. In the present study, a new CTL, Sp CTL5, was identified from the hepatopancreas of the mud crab Scylla paramamosain. The open reading frame of Sp CTL5 comprised 762 bp, encoding a polypeptide of 253 amino acids with a putative signaling peptide of 20 amino acids. The predicted Sp CTL5 protein contained a single CRD. Sp CTL5 transcripts were distributed in all examined tissues, with the highest level being detected in the hepatopancreas. Upon challenging with Vibrio alginolyticus , the mRNA levels of Sp CTL5 in the hepatopancreas were up-regulated. The recombinant protein of Sp CTL5 could agglutinate three Gram-positive bacteria and three Gram-negative bacteria in the presence of Ca2+. Furthermore, hemagglutination analysis showed that the recombinant protein of Sp CTL5 can agglutinate rabbit erythrocytes. This study indicated that Sp CTL5 acts as a pattern recognition receptor for the innate immune response which protects S. paramamosain from bacterial infection. Moreover, these findings also provide information to further our understanding of the innate immunology of invertebrates. • Sp CTL5 might be involved in the innate immune response. • Sp CTL5 can agglutinate Gram-positive and Gram-negative bacteria. • Sp CTL5 acts as a pattern recognition receptor with Ca2+ dependently. [ABSTRACT FROM AUTHOR]

In invertebrates, both fibrinogen-related proteins (FREPs) and C-type lectins are acknowledged to act as pattern recognition receptors (PRRs) to participate particularly in an innate immunity. Hereby, a unique C-type lectin designated as FmLFd was isolated from the hemocytes of Fenneropenaeus merguiensis. FmLFd contained one open reading frame which encoding a peptide of 312 amino acid residues and a signal peptide of 18 amino acids. The primary sequence of FmLFd was composed of a fibrinogen-like domain (Fd) with a Ca2+-binding site and possessing specificity to bind N-acetyl glucosamine (GlcNAc). The FmLFd transcripts were detected mainly in hemocytes of healthy shrimp. The expression of FmLFd was significantly up-regulated upon challenge shrimp with Vibrio parahaemolyticus and Vibrio harveyi which more potent than by white spot syndrome virus (WSSV). The knocking down shrimp with FmLFd double-stranded RNA caused dramatical gene down-regulation. The gene silencing with co-injection of pathogens resulted in reduction of the shrimp survival rate. Recombinant protein of FmLFd (rFmLFd) could agglutinate and bind directly to both Gram-negative and Gram-positive bacteria in a Ca2+-dependent manner and showed the sugar specificity to GlcNAc and bacterial saccharides; peptidoglycan (PGN), lipopolysaccharide (LPS) and lipoteichoic acid (LTA). Recombinant protein of Fd domain (rFd) displayed the lower activity and specificity only to PGN. The binding between recombinant proteins of FmLFd and its domain confirming by ELISA demonstrated that both rFmLFd and rFd could bind to PGN, LPS and LTA with the highest affinity respected to PGN including a less extent of rFd. Besides, rFmLFd but not rFd could bind to WSSV proteins with the highest binding affinity to capsid VP15 and decreasing in order to envelope VP28 and tegument VP39A, respectively. It was presumed that entire molecule of FmLFd exhibited the antimicrobial ability by inhibiting the growth of pathogenic V. parahaemolyticus and this action was not affected by GlcNAc. Otherwise, FmLFd, a lectin containing fibrinogen-like domain, was firstly reported to be capable of promoting encapsulation by hemocytes. Altogether, we concluded that FmLFd belonged to a FREP family indentified by the existence of a conserved fibrinogen-like domain with possessing an ability to bind GlcNAc. It was a new C-type lectin existed in F. merguiensis and might presumably act as a kind of PRRs to participate in the shrimp immune defense towards bacterial and viral pathogens. • FmLFd expression is extremely up-regulated upon Vibrio parahaemolyticus challenge. • Gene silencing by dsRNA inhibits severely FmLFd transcription and raises mortality. • rFmLFd has activities of agglutination, direct binding and antibacterial ability. • rFmLFd but not its domain displays firstly to promote encapsulation by hemocytes. • FmLFd containing fibrinogen-like domain serves as PRR against pathogens. [ABSTRACT FROM AUTHOR]

C-type lectins (CTLs) are pattern recognition receptors (PRRs) that are important in invertebrate innate immunity for the recognition and elimination of pathogens. Although they were reported in many shrimp, C-type lectins subfamily contain a large number of members with different functions that need to research in deep. In this present study, a new type of CTL, PmCL1 with 861 bp long full-length cDNA, that encodes a protein with 164-amino acid from a 495-bp open reading frame, was isolated and characterized from tiger shrimp (Penaeus monodon). The mRNA transcript of PmCL1 showed the highest expression in the hepatopancreas, whereas it was barely detected in the ovary. After the shrimp were stimulated by Vibrio harveyi and Vibrio anguillarum , PmCL1 expression in the hepatopancreas and gill was significantly upregulated. A carbohydrate-binding assay revealed the specificity of PmCL1 for pathogen-associated molecular patterns (PAMPs) that included peptidoglycan (PGN) and lipopolysaccharide (LPS), and saccharides that included d -glucose, galactosamine, α-lactose, treholose, and d -mannose. Recombinant PmCL1 agglutinated gram-positive (Staphylococcus aureus) and gram-negative bacteria (V. harveyi , V. anguillarum , Vibrio alginolyticus , Vibrio parahemolyticus , Vibrio vulnificus , and Aeromonas hydrophila) in the presence of calcium ions and enhanced the efficiency of clearing the invading bacteria. Collectively, our results suggested that PmCL1 might play an important role as a pattern recognition receptor (PRR) in the immune response towards pathogen infections, as well as the response towards ammonia nitrogen stress. • A PmCL1 gene belongs to the C-type lectin subfamilies and was up-regulated by gram-positive and gram-negative bacteria. • Ammonia-N stress significantly influenced the mRNA levels of PmCL1 in the tissues. • RPmCL1 had specificity to various carbohydrates and PAMPs. • RPmCL1 could induce agglutination of bacteria in the presence of calcium ion. • RPmCL1 could enhance the efficiency of clearing the invading bacteria in vivo. [ABSTRACT FROM AUTHOR]

Abstract Galactoside-binding lectin (galectin) is a type of pathogen recognition molecule that occupies an important position in the invertebrate innate immunity system. Our previous study has identified a galectin gene in mollusk Solen grandis (SgGal-1) and illustrated its potential roles in innate immunity. By the functional study using recombinant protein and specific antibody, here, we confirmed the pivotal roles of SgGal-1 in immune defense of S. grandis. SgGal-1 protein was expressed in many tested tissues including gill, mantle, hepatopancreas and gonad, except hemocytes and muscle. The recombinant SgGal-1 (rSgGal-1) bound PGN and β-glucan instead of LPS in vitro , and it further caused significant agglutination of five different microbes, suggesting SgGal-1 served as a pattern recognition receptor (PRR) involved in immune defense of mollusk. Furthermore, SgGal-1 recruited hemocytes to encapsulate, which was blocked by anti-rSgGal-1 serum. In the meantime, rSgGal-1 as well as promoted the phagocytosis of hemocytes against Escherichia coli in vitro. All these results suggested that SgGal-1 in S. grandis not only acted as a PRR recognizing microbes but also directly participated in the process of immune opsonization to protect the host from pathogenic infection. Highlights • Galactoside-binding lectin is a multifunctional protein in Solen grandis. • SgGal-1 is distributed in many different tissues. • SgGal-1 serves as a PRR to bind PGN and glucan. • SgGal-1 involves in the anti-microbial response through agglutination. • SgGal-1 acts as an opsonin mediating encapsulation and phagocytosis of hemocytes. [ABSTRACT FROM AUTHOR]

C-type lectins are a member of pattern recognition receptors (PRRs) that can interact with pathogen-associated molecular patterns of invading microorganisms by using their conserved motifs in carbohydrate recognition domain (CRD). The binding can trigger various immune responses in both direct and indirect mechanisms. Hereby, an ultimate C-type lectin with dual CRDs each of which containing a different motif was identified from hepatopancreas of Fenneropenaeus merguiensis (mentioned as FmLC6). The full-length cDNA of FmLC6 consisted of 1148 bp comprising one 1005 bp open reading frame (ORF) encoding a signal peptide and a mature protein of 317 residues. FmLC6 was composed of two CRDs with a highly conserved QPD (Gln-Pro-Asp) motif and one variant EPQ (Glu-Pro-Gln) motif for illustrating the carbohydrate binding affinity. The transcription of FmLC6 was detected only in hepatopancreas of normal shrimp. After injection with pathogens or immunostimulants, the expression of FmLC6 was significantly up-regulated and reached the highest level at 12 h post-injection except with lipoteichoic acid challenge. The FmLC6 expression was severely suppressed by knockdown based-silencing. This gene silencing with co-injection by Vibrio parahaemolyticus caused increasing in cumulative mortality and reduction of the median lethal time. Purified recombinant proteins of an entire ORF and two individual CRDs of FmLC6 produced in Escherichia coli could induce a broad spectrum of microbial agglutination with calcium dependence. The agglutination induced by rFmLC6, rCRD1 and rCRD2 was suppressed by galactose plus mannose, galactose and mannose, respectively which this event was confirmed by the inhibition of hemagglutination. All three recombinant proteins possessed ability to inhibit the bacterial growth with a dose-response. Purified rFmLC6 could bind directly to white spot syndrome virus particles and also its recombinant proteins including VP15, VP39A and VP28 with different affinity. Altogether, these results indicate that FmLC6 acts as a PRR to recognize invading microorganisms and leads to mediating the immune response to cooperation in pathogenic elimination via the binding, agglutination and antimicrobial activity. [ABSTRACT FROM AUTHOR]

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. • Expression profiles of 36 CTLs of Helicoverpa armigera after the infection by fungi were analyzed. • rHaCTLs were able to bind to Metarhizium rileyi conidia and hyphal bodies. • rHaCTLs agglutinate conidia and hyphal bodies in a calcium dependent manner. • Some sugars can inhibit the binding of HaCTLs to M. rileyi. • HaCTLs play significant role as PRRs in the defense of H. armigera against M. rileyi infection. [ABSTRACT FROM AUTHOR]

As a type of pattern-recognition proteins, lectins perform important functions in the innate immunity of crustaceans, including prawns. Although several reports showed that C-type lectin domain family (CLEC) importantly functions in host–pathogen interactions, limited research has focused on CLEC in Macrobrachium rosenbergii . In the present study, a new single CRD containing CLEC (designated as MrLec ) was reported in freshwater prawns, M. rosenbergii . The full-length cDNA of MrLec consisted of 1027 bp with an open reading frame of 801 bp, which encoded a peptide of 266 amino acid residues. Genomic sequence for MrLec was also obtained from the M. rosenbergii , which contain 4 exons and 3 introns. MrLec was found to contain a single carbohydrate-recognition domain with an EPN motif. MrLec was ubiquitously distributed in various tissues of a normal prawn, particularly in the hepatopancreas and gills. MrLec expression in the gills was significantly upregulated after a challenge with Vibrio parahaemolyticus and downregulated at 24 h after MrLec RNA interference ( MrLec -RNAi). The expression levels of some AMPs, including antilipopolysaccharide factor 1 ( Alf1) and lysozyme 2 ( Lyso2 ), also markedly decreased after MrLec -RNAi. Recombinant MrLec can agglutinate (Ca 2+ -dependent) and bind both Gram-negative and Gram-positive bacteria. Results suggested that MrLec participates in the recognition of invading pathogens and functions in the immune response of prawn against pathogen infections. [ABSTRACT FROM AUTHOR]

In the immune system, C-type lectins, as pattern recognition receptors, have an important function. Carbohydrate-recognition domains (CRDs) endow C-type lectins with the function of recognizing and scavenging non-self factors. In the present study, a new C-type lectin (designated as PtCTL-9 according to the order of discovery) from swimming crab (Portunus trituberculatus) was characterized. QPN (Gln-Pro-Asn) and FHS (Phe-His-Ser) were identified as the key motifs that determine carbohydrate binding. Motif QPN was mutated to QPD (Gln-Pro-Asp) (M1) and EPN (Glu-Pro-Asn) (M2) to study its immune function and for comparative analysis. The results showed that PtCTL-9 displayed broad non-self immunity. PtCTL-9 could also function as an opsonin to promote phagocytosis and the in vitro encapsulation of hemocytes. These results indicated that PtCTL-9 has an extensive nonself-recognition ability, regulates pathogen clearance, and its QPN motif is important in PtCTL-9's immune function. • A C-type lectin PtCTL-9 with a novel QPN motif was identified from Portunus trituberculatus. • PtCTL-9 possessed strong binding activity to nonself particles while its two mutants displayed weak binding activity. • PtCTL-9 inhibited the growth of S. cerevisiae. • PtCTL-9 promoted phagocytosis and encapsulation activity of hemocytes in vitro. [ABSTRACT FROM AUTHOR]

The complement system represents a crucial part of innate immunity. It contains a diverse range of soluble activators, membrane-bound receptors, and regulators. Its principal function is to eliminate pathogens via activation of three distinct pathways: classical, alternative, and lectin. In the case of viruses, the complement activation results in effector functions such as virion opsonisation by complement components, phagocytosis induction, virolysis by the membrane attack complex, and promotion of immune responses through anaphylatoxins and chemotactic factors. Recent studies have shown that the addition of individual complement components can neutralise viruses without requiring the activation of the complement cascade. While the complement-mediated effector functions can neutralise a diverse range of viruses, numerous viruses have evolved mechanisms to subvert complement recognition/activation by encoding several proteins that inhibit the complement system, contributing to viral survival and pathogenesis. This review focuses on these complement-dependent and -independent interactions of complement components (especially C1q, C4b-binding protein, properdin, factor H, Mannose-binding lectin, and Ficolins) with several viruses and their consequences. [ABSTRACT FROM AUTHOR]

• A sheep C-type lectin receptor (CTLR)-Fc fusion protein library was established. • This novel library is a tool to screen for CTLR interactions with sheep pathogens. • Several ovine CTLRs share ligand preferences with the respective murine orthologs. • The utility of the CTLR-Fc library was tested with Mycoplasma mycoides subsp. capri. C-type lectin receptors (CTLRs) are pattern recognition receptors which are important constituents of the innate immunity. However, their role has mostly been studied in humans and in mouse models. To bridge the knowledge gap concerning CTLRs of veterinary relevant species, a novel ovine CTLR hFc-fusion protein library which allows in vitro ligand identification and pathogen binding studies has been established. Its utility was tested with known ligands of corresponding murine CTLRs in ELISA- and flow cytometry based binding studies. The ovine CTLR-hFc library was subsequently used in a proof-of-principle pathogen binding study with the ruminant pathogen Mycoplasma mycoides subsp. capri. Some ovine CTLRs, such as Dendritic Cell Immunoreceptor (DCIR, Clec4a), Macrophage C-Type Lectin (MCL, Clec4d) and Myeloid Inhibitory C-Type Lectin-Like Receptor (MICL, Clec12a) were identified as possible candidate receptors whose role in Mycoplasma recognition can now be unraveled in further studies. This study thus shows the utility of this novel ovine CTLR-hFc fusion protein library to screen for CTLR/pathogen interactions. [ABSTRACT FROM AUTHOR]