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As lower vertebrates, fish have both innate and adaptive immune systems, but the role of the adaptive immune system is limited, and the innate immune system plays an important role in the resistance to pathogen infection. C-type lectins (CLRs) are one of the major pattern recognition receptors (PRRs) of the innate immune system. CLRs can combine with pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs) to trigger NF-κB signaling pathway and exert immune efficacy. In this study, Ssclec12b and Ssclec4e of the C-type lectins, were found to be significantly up-regulated in the transcripts of Sebastes schlegelii macrophages stimulated by bacteria. The identification, expression and function of these lectins were studied. In addition, the recombinant proteins of the above two CLRs were obtained by prokaryotic expression. We found that rSsCLEC12B and rSsCLEC4E could bind to a variety of bacteria in a Ca2+-dependent manner, and promoted the agglutination of bacteria and blood cells. rSsCLEC12B and rSsCLEC4E assisted macrophages to recognize PAMPs and activate the NF-κB signaling pathway, thereby promoting the expression of inflammatory factors (TNF-α , IL-1β , IL-6 , IL-8) and regulating the early immune inflammation of macrophages. These results suggested that SsCLEC12B and SsCLEC4E could serve as PRRs in S. schlegelii macrophages to recognize pathogens and participate in the host antimicrobial immune process, and provided a valuable reference for the study of CLRs involved in fish innate immunity. • The expression changes of Ssclec12b and Ssclec4e before and after bacterial stimulation were investigated in immunologic tissues. • The bacterial binding activity and the Ca2+-dependent bacterial agglutination activity of rSsCLEC12B and rSsCLEC4E had been demonstrated, which proved the important role in the process of S. schlegelii resisting pathogen infection. • The expression of p65 , TRAF3 , TAK1 and NIK1 of NF-κB signaling pathway was significantly up-regulated in macrophages infected with A. johnsonii. The addition of rSsCLEC12B and rSsCLEC4E further increased the expression of the above four genes. • rSsCLEC12B and rSsCLEC4E significantly increased the expression of pro-inflammatory factors in macrophages. [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]

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 (Mn Lec3). The full-length cDNA of Mn Lec3 was 1150 bp with an open reading frame of 723 bp, encoding 240 amino acids. Mn Lec3 protein contained a signal peptide and one single carbohydrate-recognition domain (CRD). Mn Lec3 transcripts were widely distributed at the exoskeleton all over the body. Significant up-regulation of Mn Lec3 in exoskeleton after Aeromonas hydrophila challenged suggested the involvement of Mn Lec3 as well as the possible function of the exoskeleton in immune response. In vitro tests with recombinant Mn Lec3 protein (r Mn Lec3) 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, r Mn Lec3 significantly promoted phagocytic ability of hemocytes against A. hydrophila in vivo. What's more, Mn Lec3 interference remarkably impaired the survivability of the prawns when infected with A. hydrophila. Collectively, these results ascertained that Mn Lec3 derived from exoskeleton took an essential part in immune defense of the prawns against invading bacteria as a PRR. • A novel CTL (Mn Lec3) was identified from the exoskeleton of the oriental river prawn Macrobrachium nipponense. • Mn Lec3 plays a vital role in the immune response of the prawn. • 3.The exoskeleton might be more active in the immune response of the prawn by generating immunologic factors. [ABSTRACT FROM AUTHOR]

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 Hd Clec), 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 Hd Clec 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 Hd Clec. The mRNA transcripts of Hd Clec 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 Hd Clec mRNA in hemocytes was significantly up-regulated after Vibrio harveyi challenge. Recombinant Hd Clec protein (r Hd Clec) could bind lipopolysaccharide (LPS) and peptidoglycan (PGN) in vitro in the presence of Ca2+. Coinciding with the PAMPs binding assay, r Hd Clec 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, r Hd Clec could significantly elicit the chemotactic response of hemocytes in vitro. And the phagocytosis and encapsulation ability of hemocytes could be significantly enhanced by r Hd Clec. All these results showed that Hd Clec 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. • A single-CRD C-type lectin (Hd CLec) with novel NPN motif was identified from abalone. • The mRNA of Hd CLec was significantly up-regulated post Vibrio harveyi challenge. • R Hd CLec displayed broad microbe agglutination spectrum. • R Hd CLec could elicit the chemotactic response of hemocytes in vitro. • R Hd CLec could function as an opsonin enhancing phagocytosis and encapsulation activities of hemocytes. [ABSTRACT FROM AUTHOR]

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. • In this study, a new CTL with two distinct C-type lectin domains (CTLDs) from Penaeus vannamei , designated as PvMR1 was identified. • The observations indicated that PvMR1 plays an important role in innate immune responses of Penaeus vannamei. • Considering that PvMR1 functioned as a pattern recognition receptor that participates in innate immunity, we suggest that consideration for the strategies used to control Penaeus vannamei aquaculture disease. [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]

C-type lectins (CTLs) are important pathogen pattern recognition receptors that recognize carbohydrate structures. In present study, a C-type lectin domain family 4 member E-like gene from turbot, which tentatively named SmCLEC4E-like (SmCLEC4EL), was identified, and the expressional and functional analyses were performed. In our results, SmCLEC4EL showed conserved synteny with CLEC4E-like genes from several fish species in genome, and possessed a typical type II transmembrane CTL architecture: an N-terminal intracellular region, a transmembrane domain and a C-terminal extracellular region which contained a predicted carbohydrate recognition domain (CRD). In addition, SmCLEC4EL exhibited the highest expression level in spleen in healthy fish, and showed significantly induced expression in mucosal tissues, intestine and skin, under bacteria challenge. Finally, the recombinant SmCLEC4EL protein combined with LPS, PGN, LTA and five different kinds of bacteria in a dose-dependent manner, and agglutinated these bacteria strains in the presence of calcium. These findings collectively demonstrated that SmCLEC4EL, a calcium-dependent CTL, could function as a pattern recognition receptor in pathogen recognition and participate in host anti-bacteria immunity. • SmCLEC4EL showed conserved synteny to its counterparts in other vertebrates. • SmCLEC4EL was ubiquitously expressed in turbot tissues. • SmCLEC4EL showed different expression patterns following different bacterial challenge. • SmCLEC4EL had strong binding ability to LPS, LTA, PGN, and five different kinds of bacteria in a dose-dependent manner. [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]

In the present study, two C-type lectins (designated as VpClec-3 and VpClec-4) were identified and characterized from the manila clam Venerupis philippinarum. Multiple alignment and phylogenetic relationship analysis strongly suggested that VpClec-3 and VpClec-4 belong to the C-type lectin family. In nonstimulated clams, the VpClec-3 transcript was dominantly expressed in the hepatopancreas, while the VpClec-4 transcript was mainly expressed in gill tissues. Both VpClec-3 and VpClec-4 mRNA expression was significantly upregulated following Vibrio anguillarum challenge. Recombinant VpClec-4 (rVpClec-4) was shown to bind lipopolysaccharide (LPS) and glucan in vitro , whereas recombinant VpClec-3 (rVpClec-3) only bound to glucan. In addition, rVpClec-3 and rVpClec-4 displayed broad agglutination activities towards Vibrio harveyi , Vibrio splendidus and V. anguillarum , while no agglutination activities towards Enterobacter cloacae or Aeromonas hydrophila were observed in rVpClec-3. Moreover, hemocyte phagocytosis was significantly enhanced by rVpClec-3 and rVpClec-4. All the results showed that VpClecs function as pattern recognition receptors (PRRs) with distinct recognition spectra and are potentially involved in the innate immune responses of V. philippinarum. • Two C-type lectins were identified from the manila clam Ruditapes philippinarum. • VpClecs are C-type lectins with different PAMPs binding spectrum. • VpClecs can agglutinate Gram-positive and Gram-negative bacteria. • VpClecs can function as opsonins to prompt phagocytosis against non-self. [ABSTRACT FROM AUTHOR]

C-type lectins (CTLs) play important roles in innate immune system of crustaceans as pattern recognition receptors (PRRs). In this study, a novel CTL gene was obtained from the red swamp crayfish, Procambarus clarkii , designated as PcLec. PcLec encodes a peptide with 175 amino acids, with a signal peptide and a single carbohydrate recognition domain (CRD). The PcLec transcripts were specifically expressed in crayfish stomach and were induced by bacterial challenge. In vitro assays with recombinant PcLec protein revealed that it had bacterial binding activity, polysaccharide binding activity, bacterial agglutination activity, and antimicrobial activity. Most importantly, PcLec knockdown significantly impaired the survivability of crayfish upon oral infection with its pathogen A. hydrophila. According to these results, we infer that the PcLec plays a crucial role in antibacterial defense of crayfish. • PcLec is stomach specific and responds to bacterial challenge. • PcLec has direct antimicrobial activity against both Gram+ and Gram-bacteria. • PcLec knockdown impaired the survivability of crayfish upon oral infection with bacteria. [ABSTRACT FROM AUTHOR]

In the study, two c-type lectins were identified and characterized from the manila clam Venerupis philippinarum (designed as VpClec-1 and VpClec-2, respectively). Multiple alignments and phylogenetic analysis strongly suggested that they were new members of the c-type lectin superfamily. In normal tissue of clams, both VpClec-1 and VpClec-2 transcripts were highly expressed in the tissue of hepatopancreas. After Vibrio anguillarum challenge, the temporal expression of both VpClec-1 and VpClec-2 transcripts was up-regulated in the hemocytes of manila clams. The recombinant protein VpClec-1 (rVpClec-1) showed obvious binding activities to lipopolysaccharide (LPS), peptidoglycan (PGN), glucan and zymosan in vitro , while the recombinant protein VpClec-2 (rVpClec-2) could only bind LPS, glucan and zymosan. Coinciding with the PAMPs binding assay, both rVpClec-1 and rVpClec-2 displayed broad agglutination and antibacterial activities towards Vibrio harveyi , Vibrio splendidus , Vibrio anguillarum , Enterobacter cloacae and Aeromonas hydrophila. Moreover, the phagocytosis and encapsulation ability of hemocytes could be significantly enhanced by rVpClec-1 and rVpClec-2. Notably, the rVpClec-1 but not rVpClec-2 elicited a chemotactic response from hemocytes. All the results showed that VpClec-1 and VpClec-2 functioned as pattern recognition receptors (PRRs) with distinct recognition spectrum, and involved in the innate immune responses of manila clams. • Two c-type lectins (VpClec-1 and VpClec-2) were identified from the Manila clam Ruditapes philippinarum. • Both VpClec-1 and VpClec-2 were highly expressed in hepatopancreas of healthy Manila clam. • Both VpClec-1 and VpClec-2 showed a broad spectrum of microbial binding and opsonic activities. [ABSTRACT FROM AUTHOR]

C-type lectins (CTLs) are a group of lectins with at least one carbohydrate recognition domain (CRD), the binding of which to carbohydrates requires the presence of calcium ions. CTLs generally function as pattern recognition receptors (PRRs), essentially participating in innate immunity. In the current study, a novel CTL termed LvCTL5 was identified from Pacific white shrimp Litopenaeus vannamei , which shared sequence identities with other crustacean CTLs. LvCTL5 was highly expressed in hepatopancreas and could be activated by infection with bacteria, virus and fungi. The recombinant LvCTL5 protein purified from E. coli showed microbiostatic and agglutination activities against bacteria and fungi in vitro. Silencing of LvCTL5 in vivo could significantly affect expression of a series of immune effector genes and down-regulate the phagocytic activity of hemocytes. Compared with controls, the LvCTL5-silenced shrimp were highly susceptible to Vibrio parahaemolyticus and white spot syndrome virus (WSSV) infections. These suggest that LvCTL5 has microbiostatic and immune regulatory activities and is implicated in antiviral and antibacterial responses. • Identification of a novel C-type lectin gene (LvCTL5) from Litopenaeus vannamei. • LvCTL5 protein has microbiostatic and immune regulatory functions. • LvCTL5 is involved in antibacterial and antiviral responses. [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]

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

Rimicaris exoculata (Decapoda: Bresiliidae) is one of the dominant species of hydrothermal vent communities, which inside its gill chamber harbors ectosymbioses with taxonomic invariability while compositional flexibility. Several studies have revealed that the establishment of symbiosis can be initiated and selected by innate immunity-related pattern recognition receptors (PRRs), such as C-type lectins (CTLs). In this research, a CTL was identified in R. exoculata (termed RCTL), which showed high expression at both mRNA and protein levels in the scaphognathite, an organ where the ectosymbionts are attached outside its setae. Linear correlationships were observed between the relative quantities of two major symbionts and the expression of RCTL based on analyzing different shrimp individuals. The recombinant protein of RCTL could recognize and agglutinate the cultivable γ -proteobacterium of Escherichia coli in a Ca2+-dependent manner, obeying a dose-dependent and time-cumulative pattern. Unlike conventional crustacean CTLs, the involvement of RCTL could not affect the bacterial growth, which is a key issue for the successful establishment of symbiosis. These results implied that RCTL might play a critical role in symbiotic recognition and attachment to R. exoculata. It also provides insights to understand how R. exoculata adapted to such a chemosynthesis-based environment. • Indispensable ectosymbionts occur in the hydrothermal vent shrimp R. exoculata. • High expression of RCTL is linearly correlated with quantities of two major symbionts. • rRCTL selectively recognize and agglutinate E. coli in a Ca2+-dependent manner. • RCTL contributes to selectivity and stability of symbioses in R. exoculata. [ABSTRACT FROM AUTHOR]

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. • A novel C-type lectin from blunt snout bream was identified and characterized. • MaCTL expression were significantly upregulated after immune stimulation. • rMaCTL agglutinated various bacteria in vitro in the presence of Ca2+. • rMaCTL bound distinct bacteria and some carbohydrates such as LPS and PGN. • rMaCTL exhibited antimicrobial activity by inhibiting the growth of bacteria. [ABSTRACT FROM AUTHOR]

Abstract The Manila clam, Ruditapes philippinarum , is one of the most commercially important marine bivalves. C-type lectins (CTLs) are pattern recognition receptors (PRRs) that play important roles in the identification and elimination of pathogens by the innate immune system. In this study, a new CTL (RpCTL) was identified in the Manila clam, R. philippinarum. The full-length RpCTL cDNA is 802 bp, with an open reading frame of 591 bp, encoding 196 amino acids, including an N-terminal signal peptide and a carbohydrate recognition domain (CRD). RpCTL contains conserved CRD disulfide bonds involving four cysteine residues (Cys30–Cys104, Cys124, and Cys132), and the EPN (Glu94–Pro95–Asn96) and WND (Trp119–Asn120–Asp121) motifs. Quantitative reverse transcription (RT)–PCR detected RpCTL transcripts mainly in the gill, siphon, and hepatopancreas in three shell-color strains (zebra, white, and white–zebra strains) and two unselected populations of R. philippinarum , and the gene was highly expressed in the hepatopancreas after lipopolysaccharide treatment. Antimicrobial activity assays of recombinant RpCTL against both Gram-positive and Gram-negative bacteria showed that RpCTL inhibits microorganismal growth. In a survival test, RpCTL inhibited and killed Vibrio anguillarum in R. philippinarum. These results suggest that RpCTL participates in the pathogen identification process of R. philippinarum as a PRR and in its immune defense system. Highlights • Full length cDNA of RpCTL was cloned from the Manila clam by RACE method. • The mRNA transcripts of RpCTL expressed at the highest level in hepatopancreas. • Expression analysis of RpCTL was performed in clam after lipopolysaccharides (LPS) challenge. [ABSTRACT FROM AUTHOR]

C-type lectins are a superfamily of Ca 2+ -dependent carbohydrate-recognition proteins, which play crucial roles in innate immunity including nonself-recognition and pathogen elimination. In the present study, two single-CRD containing C-type lectins were identified from swimming crab Portunus trituberculatus (designated as PtCTL-2 and PtCTL-3). The open reading frame (ORF) of PtCTL-2 encoded polypeptides of 485 amino acids with a signal peptide and a single carbohydrate-recognition domain (CRD), while PtCTL-3's ORF encoded polypeptides of 241 amino acids with a coiled-coil region and a single-CRD. The key motifs determining carbohydrate binding specificity in PtCTL-2 and PtCTL-3 were EPR (Glu-Pro-Arg) and QPD (Gln-Pro-Asp). EPR is a motif being identified for the first time, whereas QPD is a typical motif in C-type lectins. Different PAMPs binding features of the two recombinant proteins - PtCTL-2 (rPtCTL-2) and PtCTL-3 (rPtCTL-3) have been observed in our experiments. rPtCTL-2 could bind three pathogen-associated molecular patterns (PAMPs) with relatively high affinity, including glucan, lipopolysaccharide (LPS) and peptidoglycan (PGN), while rPtCTL-3 could barely bind any of them. However, rPtCTL-2 could bind seven kinds of microbes and rPtCTL-3 could bind six kinds in microbe binding assay. Moreover, rPtCTL-2 and rPtCTL-3 exhibited similar agglutination activity against Gram-positive bacteria, Gram-negative bacteria and fungi in agglutination assay. All these results illustrated that PtCTL-2 and PtCTL-3 could function as important pattern-recognition receptors (PRR) with broad nonself-recognition spectrum involved in immune defense against invaders. In addition, the results of carbohydrate binding specificity showed that PtCTL-2 with novel key motif had broad carbohydrate binding specificity, while PtCTL-3 with typical key motif possessed different carbohydrate binding specificity from the classical binding rule. Furthermore, PtCTL-2 and PtCTL-3 could also function as opsonin to enhance encapsulation of hemocytes against Ni-NTA beads. [ABSTRACT FROM AUTHOR]

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. • LvCTL7 could directly agglutinate bacterial pathogens. • LvCTL7 could regulate the expression of antibacterial-related genes. • LvCTL7 is involved in the innate immune response against Vibrio infection. [ABSTRACT FROM AUTHOR]

Lectins are a superfamily of carbohydrate-recognition proteins that bind to specific carbohydrate structures and play significant roles in immune recognition and clearance of invaders. In the study, we investigated the potential mechanisms of PAMP binding and opsonic activities of a c-type lectin and a sialic acid-binding lectin from manila clam Venerupis philippinarum (designed as VpCTL and VpSABL). Both recombinant proteins (rVpCTL and rVpSABL) could bind LPS, PGN, glucan and zymosan in vitro. Coinciding with the PAMPs binding assay, a broad agglutination spectrum was displayed by rVpSABL including gram-positive bacteria Staphyloccocus aureus , gram-negative bacteria Escherichia coli , Vibrio parahaemolyticus , Vibrio harveyi , Pseudomonas putida , Proteus mirabilis and fungi Pichia pastoris , while no agglutinative activities on P. mirabilis and P. putida was observed in rVpCTL. Moreover, the phagocytosis and encapsulation ability of hemocytes could be significantly enhanced by rVpCTL and rVpSABL. More remarkable, VpCTL and VpSABL were highly detected in all the examined tissues, especially in gills and hepatopancreas. All the results showed that VpCTL and VpSABL could function as pattern recognition receptors (PRRs) with distinct recognition spectrum, perhaps involved in the innate immune responses of V. philippinarum. • Both rVpCTL and rVpSABL could bind LPS, PGN, glucan and zymosan in vitro. • A broad agglutination spectrum was displayed by recombinant lectins, especially by rVpSABL. • The phagocytosis and encapsulation ability of hemocytes could be significantly enhanced by rVpCTL and rVpSABL. [ABSTRACT FROM AUTHOR]

C-type lectins (CTLs) are important pattern recognition receptors (PRRs) that play vital roles in innate immunity. In teleosts, a number of CTLs have been reported, but their in vivo effects on host defense are still limited. In this study, a CTL homolog (SsLec1) was identified from black rockfish, Sebastes schlegelii , and its structure, expression and biological function was analyzed. The open reading frame of SsLec1 is 633 bp, with a 5’- untranslated region (UTR) of 36 bp and a 3′- UTR of 117 bp. The deduced amino acid sequence of SsLec1 shares the highest overall identity (73.20%) with the CTL of Oplegnathus fasciatus . SsLec1 possesses conserved CTL features, including a carbohydrate-recognition domain, four disulfide bond-forming cysteine residues, the mannose-type carbohydrate-binding motif, the conserved calcium binding sites and a putative signal peptide. The expression of SsLec1 was highest in liver and could be induced by experimental infection with Listonella anguillarum . Recombinant SsLec1 (rSsLec1) purified from E. coli was able to bind and agglutinate the Gram-negative fish pathogens Vibrio ichthyoenteri and Vibrio vulnificus . The agglutinating ability of rSsLec1 was abolished in the presence of mannose or ethylenediaminetetraacetic acid. Further analysis showed that rSsLec1 could enhance phagocytosis by macrophages. In vivo experiments indicated that rSsLec1 could inhibit bacterial infection and promote viral invasion. Taken together, these results suggest that SsLec1 is a novel CTL that possesses apparent immunoregulation property and plays a critical role in host defense against pathogens invasion. [ABSTRACT FROM AUTHOR]