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• 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]

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]

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]

• 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]