Identification, cloning and tissue localization of a rainbow trout (Oncorhynchus mykiss) intelectin-like protein that binds bacteria and chitin

Antibacterial Activity of Rainbow Trout Plasma: In Vitro Assays and Proteomic Analysis

The objective of this study was to investigate the bactericidal activity of blood plasma from cultured rainbow trout obtained from two different fish farms. Plasma from trout naturally infected with the bacterial pathogen Flavobacterium psychrophilum was found to inhibit the growth of Aeromonas hydrophila in vitro. Incubation of A. hydrophila in bacteriostatic trout plasma resulted in agglutination and growth retardation, without causing massive damage to the cell membrane. The proteome of the plasma with high antimicrobial activity revealed an abundance of high-density apolipoproteins, some isoforms of immunoglobulins, complement components C1q and C4, coagulation factors, lectins, periostin, and hemoglobin. Analysis of trout proteins retained on A. hydrophila cells revealed the presence of fish immunoglobulins, lectins, and complement components on bacteria whose growth was inhibited, although the native membrane attack complex of immunised trout plasma did not assemble effectively, resulting in a weak bactericidal effect. Furthermore, this study examined the bacterial response to trout plasma and suggested that the protein synthesis pathway was the target of antimicrobial proteins from fish blood. Taken together, these findings illustrate the advantages of the affinity approach for understanding the role of plasma proteins in host defence against pathogens.

Characterization of the innate immune response to Streptococcus pneumoniae infection in zebrafish

Streptococcus pneumoniae (pneumococcus) is one of the most frequent causes of pneumonia, sepsis and meningitis in humans, and an important cause of mortality among children and the elderly. We have previously reported the suitability of the zebrafish (Danio rerio) larval model for the study of the host-pathogen interactions in pneumococcal infection. In the present study, we characterized the zebrafish innate immune response to pneumococcus in detail through a whole-genome level transcriptome analysis and revealed a well-conserved response to this human pathogen in challenged larvae. In addition, to gain understanding of the genetic factors associated with the increased risk for severe pneumococcal infection in humans, we carried out a medium-scale forward genetic screen in zebrafish. In the screen, we identified a mutant fish line which showed compromised resistance to pneumococcus in the septic larval infection model. The transcriptome analysis of the mutant zebrafish larvae revealed deficient expression of a gene homologous for human C-reactive protein (CRP). Furthermore, knockout of one of the six zebrafish crp genes by CRISPR-Cas9 mutagenesis predisposed zebrafish larvae to a more severe pneumococcal infection, and the phenotype was further augmented by concomitant knockdown of a gene for another Crp isoform. This suggests a conserved function of C-reactive protein in anti-pneumococcal immunity in zebrafish. Altogether, this study highlights the similarity of the host response to pneumococcus in zebrafish and humans, gives evidence of the conserved role of C-reactive protein in the defense against pneumococcus, and suggests novel host genes associated with pneumococcal infection.

Biochemical and ligand binding properties of recombinant Xenopus laevis cortical granule lectin-1

Intelectins are putative innate immune lectins that are found throughout chordates. The first intelectin reported was Xenopus laevis cortical granule lectin-1 (XCGL-1 or XL-35). XCGL-1 is critical in fertilization membrane development in Xenopus. Here, we explored the biochemical properties of XCGL-1. The cysteines responsible for forming intermolecular disulfide bonds were identified. XCGL-1 adopted a four-lobed structure as observed by electron microscopy. The full-length XCGL-1 and the carbohydrate recognition domain (CRD) bind galactose-containing carbohydrates at nanomolar to micromolar affinities. Molecular modeling suggested that galactoside ligands coordinated the binding site calcium ion and interacted with residues around the groove made available by the non-conserved substitution compared to human intelectin-1. Folding conditions for production of recombinant XCGL-1 CRD were also investigated. Our results not only provide new biochemical insights into the function of XCGL-1, but may also provide foundation for further applications of XCGL-1 as glycobiology tools.

Molecular properties and ligand specificity of zebrafish intelectin-2

Intelectins are immune lectins expressed in chordates, including several fish species, in which intelectins are known to be upregulated upon infection. However, the basic biochemical properties and bacteria binding specificities of several fish intelectins are not well studied. We focus our investigation on zebrafish intelectin-2 (DrIntL-2) that is predominantly expressed in the gastrointestinal tract. The disulfide-linked oligomeric state and the cysteine responsible for intermolecular disulfide bonds are identified. DrIntL-2 is a globular particle of around 30 nm. In addition to the typical exocyclic 1,2-diol ligands, DrIntL-2 binds β-1,3-glucan and recognizes Salmonella typhimurium and Pseudomonas aeruginosa. This investigation not only shed light on the fish innate immunity that will be essential for the aquaculture industry, but will also provide a foundation for further application of DrIntL-2 in bacteria detection and identification.

Novel insights into the immune regulatory effects of Megalobrama amblycephala intelectin on the phagocytosis and killing activity of macrophages

Previous studies have found that the expression level of Megalobrama amblycephala intelectin (MaINTL) increased significantly post Aeromonas hydrophila infection, and recombinant MaINTL (rMaINTL) protein could activate macrophages and enhance the phagocytosis and killing activity of macrophages. In order to reveal the immune regulatory mechanisms of MaINTL, primary M. amblycephala macrophages were treated with endotoxin-removed rMaINTL and GST-tag proteins, then total RNA were extracted and used for comparative Digital Gene Expression Profiling (DGE). 1247 differentially expressed genes were identified by comparing rMaINTL and GST-tag treated macrophage groups, including 482 up-regulated unigenes and 765 down-regulated unigenes. In addition, eleven randomly selected differentially expressed genes were verified by qRT-PCR, and most of them shared the similar expression patterns as that of DGE results. GO enrichment revealed that the differentially expressed genes were mainly concentrated in the membrane part and cytoskeleton of cellular component, the binding and signal transducer activity of molecular function, the cellular process, regulation of biological process, signaling and localization of biological process, most of which might related with the phagocytosis and killing activity of macrophages. KEGG analysis revealed the activation and involvement of differentially expressed genes in immune related pathways, such as Tumor necrosis factor (TNF) signaling pathway, Interleukin 17 (IL-17) signaling pathway, Toll-like receptor signaling pathway, and NOD like receptor signaling pathway, etc. In these pathways, TNF-ɑ, Activator protein-1 (AP-1), Myeloid differentiation primary response protein MyD88 (MyD88), NF-kappa-B inhibitor alpha (ikBɑ) and other key signaling factors were significantly up-regulated. These results will be helpful to clarify the immune regulatory mechanisms of fish intelectin on macrophages, thus providing a theoretical basis for the prevention and control of fish bacterial diseases.

Bovine Intelectin 2 Expression as a Biomarker of Paratuberculosis Disease Progression

Simple Summary

The potential of the bovine intelectin 2 as a biomarker of Mycobacterium avium subsp. paratuberculosis infection was investigated using quantitative immunohistochemical analysis of ileocecal valve samples of animals with increasing degrees of lesion severity (focal, multifocal and diffuse histological lesions) and control animals without detected lesions. Significant differences were observed in the mean number of intelectin 2 immunolabelled cells between the three histopathological types and the control. Specifically, the mean number of intelectin 2 labelled cells was indicative of disease progression as the focal group had the highest number of intelectin 2 secreting cells followed by the multifocal, diffuse and control groups indicating that intelectin 2 is a good biomarker for the different stages of Mycobacterium avium subsp. paratuberculosis infection. Quantification of bovine intelectin 2 secreting cells could constitute a good post-mortem tool, complementary to histopathology, to improve detection of Mycobacterium avium subsp. Paratuberculosis infections, especially latent forms of infection.

Abstract

Paratuberculosis (PTB), a chronic granulomatous enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP), is responsible for important economic losses in the dairy industry. Our previous RNA-sequencing (RNA-Seq) analysis showed that bovine intelectin 2 (ITLN2) precursor gene was overexpressed in ileocecal valve (ICV) samples of animals with focal (log2 fold-change = 10.6) and diffuse (log2 fold-change = 6.8) PTB-associated lesions compared to animals without lesions. This study analyzes the potential use of ITLN2, a protein that has been described as fundamental in the innate immune response to infections, as a biomarker of MAP infection. The presence of ITLN2 was investigated by quantitative immunohistochemical analysis of ICV samples of 20 Holstein Friesian cows showing focal (n = 5), multifocal (n = 5), diffuse (n = 5) and no histological lesions (n = 5). Significant differences were observed in the mean number of ITLN2 immunostained goblet and Paneth cells between the three histopathological types and the control. The number of immunolabelled cells was higher in the focal histopathological type (116.9 ± 113.9) followed by the multifocal (108.7 ± 140.5), diffuse (76.5 ± 97.8) and control types (41.0 ± 81.3). These results validate ITLN2 as a post-mortem biomarker of disease progression.

Characterization of a common carp intelectin gene with bacterial binding and agglutination activity

Intelectin (ITLN) is a type of glycan-binding lectin involved in many physiological processes and some human diseases. Here we report a common carp intelectin (cITLN). Like other orthologs, cITLN also contains a conserved fibrinogen-related domain (FReD) and a unique intelectin domain, expresses in all the tissues tested with the highest level in the hindgut, and responds to bacterial challenge in the acute phase. We also expressed cITLN in Escherichia coli (E. coli) system, and the purified recombinant cITLN could neither affect the surface of bacteria nor inhibit the growth of bacteria, but it can agglutinate both gram-positive and gram-negative bacteria in a calcium-dependent manner. The cITLN's ability of agglutination of gram-positive bacteria is stronger than that of gram-negative bacteria. This is probably because recombinant cITLN could binding peptidoglycan (PGN) with a higher degree to lipopolysaccharide (LPS). Our results of cITLN provided new insight into the function of intelectin in the intestinal mucosal immunity.

A comparative review of intelectins

Intelectin (ITLN) is a new type of glycan-binding lectin. It has been demonstrated to agglutinate bacteria probably due to its carbohydrate-binding capacity, suggesting its role in an innate immune response. It is involved not only in many physiological processes but also in some human diseases such as asthma, heart disease, inflammatory bowel disease, chronic obstructive pulmonary disease and cancer. Up to now, intelectin orthologs have been identified in placozoans, urochordatas, cephalochordates and several vertebrates, such as cyclostomata, fish, amphibians and mammals. Although the sequences of intelectins in different species are conserved, their expression patterns, quaternary structures and functions differ considerably among and within species. We summarize the evolution of the intelectin gene family, the tissue distribution, structure and functions of intelectins. We conclude that intelectin plays a role in innate immune response and there are still potential functions of intelectin awaiting discovery.

ITLN in diploid hybrid fish (Carassius auratus cuvieri ♀ × Carassius auratus red var ♂) is involved in host defense against bacterial infection

Hybrid genotypes in fish may be less susceptible to pathogenic infection. ITLN, a novel lectin, not only exhibits a regulatory role in pathogenic infection, but also participates in the regulation of teleostean immunity. In this study, ORF sequence of WR-ITLN was 945 bp and encoded 314 amino acid residues. Tissue-specific analysis revealed that the highest expression of WR-ITLN was observed in liver. Aeromonas hydrophila challenge can sharply increased WR-ITLN mRNA expression in liver, kidney and spleen. The purified WR-ITLN protein can directly bind to A. hydrophila and S. agalactiae, reduce their relative bacterial activity and limit bacterial growth in vitro in the presence of Ca²⁺. In addition, the treatment of WR-ITLN + Ca²⁺ can restrict bacterial dissemination in vivo and attenuate production of pro-inflammatory cytokines. These results indicated that WR-ITLN can confer protection against bacteria-stimulated MyD88-dependent pro-inflammatory cytokines activation in a Ca²⁺-dependent manner.

The D5 region of the intelectin domain is a new type of carbohydrate recognition domain in the intelectin gene family

Intelectin is a recently characterized soluble galactofuranose-binding lectin that exists in species ranging from amphioxus to human. Interestingly, intelectin does not contain a canonical carbohydrate-recognition domain (CRD). Therefore, we designed serial deletions of intelectin in the Chinese amphioxus (Branchiostoma belcheri tsingtauense, AmphiITLN71469) in order to identify functional regions required for carbohydrate binding. Our results revealed that Domain 5 (aa 203-302) was able to bind lipopolysaccarides (LPS) or peptidoglycan (PGN) and agglutinate bacteria as efficiently as the full-length protein. Three dimensional (3D) atomic models of Domain 5 were generated by ab initio based program QUARK and by Iterative Threading Assembly Refinement (I-TASSER) programs, in which four amino acids mediating calcium-binding (G54-G55-G56-E91) were identified by hemagglutination assay. Furthermore, a striking functional conservation of Domain 5 was detected in zebrafish intelectin 1. Taken together, our findings identified for the first time a new CRD domain in intelectin, thereby providing new knowledge leading to a better understanding of pathogen-host interactions.

Characterization and expression analysis of an intelectin gene from Megalobrama amblycephala with excellent bacterial binding and agglutination activity

Intelectin is a recently discovered lectin that plays vital roles in the innate immune response, iron metabolism and early embryogenesis. The structure, expression pattern and function of intelectin in mammals and amphibians have been well studied, while not well known in fish. In this study, we cloned a intelectin (MamINTL) gene from blunt snout bream (Megalobrama amblycephala), examined its expression patterns and explored its roles in innate immune response. The MamINTL cDNA encoded 312 amino acids, with a pro-protein of 34 kDa. Sequence analysis revealed the presence of a fibrinogen-related domain and eight conserved cysteine residues in the MamINTL. The MamINTL mRNA was detectable at various developmental stages, while it increased significantly post hatching. In healthy adult M. amblycephala, MamINTL was detected in various tissues with the highest expression in the liver. Upon challenge with Aeromonas hydrophila, significantly up-regulated expression of the MamINTL mRNA was observed in the liver, spleen, kidney, intestine and gill. In addition, increased level of MamINTL protein detected by Western Blotting was also observed in the liver, kidney and spleen, indicating the participation of MamINTL in the immune response. Immunohistochemistry analysis of the M. amblycephala liver sections showed significant changes in expression and location post infection. In addition, the recombinant MamINTL showed excellent binding and agglutination activity against GFP-expressed E. coli in a Ca²⁺-dependent manner. Generally, the present study provides clues for a better understanding of the characterization, expression patterns and functions of fish intelectins.

A zebrafish intelectin ortholog agglutinates both Gram-negative and Gram-positive bacteria with binding capacity to bacterial polysaccharide

Intelectins are glycan-binding lectins found in various species including cephalochordates, urochordates, fish, amphibians and mammals. But their detailed functions are not well studied in zebrafish which is a good model to study native immunity. In this study, we cloned a zebrafish intelectin ortholog, zebrafish intelectin 2 (zITLN2), which contains a conserved fibrinogen-related domain (FReD) in the N-terminus and the unique intelectin domain in the C-terminus. We examined the tissue distribution of zITLN2 in adult zebrafish and found that zITLN2 was expressed in various organs with the highest level in intestine. Like amphioxus intelectins, zITLN2 expression was upregulated in adult zebrafish infected with Staphylococcus aureus with the highest expression level at 12 h after challenge. Recombinant zITLN2 protein expressed in E. coli was able to agglutinate both Gram-negative and Gram-positive bacteria to similar degrees in a calcium-dependent manner. Furthermore, recombinant zITLN2 bound lipopolysaccharide (LPS) and peptidoglycan (PGN) comparably. Our work on zITLN2 provided further information to understand functions of this new family of lectins and the innate immunity in vertebrates.

Identification and characterization of a novel intelectin in the digestive tract of Xenopus laevis

The intelectin (Intl) family is a group of secretory lectins in chordates that serve multiple functions, including innate immunity, through Ca(2+)-dependent recognition of carbohydrate chains. Although six Intl family lectins have so far been reported in Xenopus laevis, none have been identified in the intestine. Using a monoclonal antibody to the Xenopus embryonic epidermal lectin (XEEL or Intl-1), I identified cross-reactive proteins in the intestines. The proteins were purified by affinity chromatography on a galactose-Sepharose column and found to be oligomers consisting of N-glycosylated 39 kDa and 40.5 kDa subunit peptides. N-terminal amino acid sequencing of these peptides, followed by cDNA cloning, identified two novel Intls (designated Intl-3 and Intl-4) that showed 59-79% amino acid identities with known Xenopus Intl family proteins. From the amino acid sequence, immunoreactivity, and properties of the recombinant protein, Intl-3 was considered the intestinal lectin identified by the anti-XEEL antibody. The purified Intl-3 protein could potentially bind to Escherichia coli and its lipopolysaccharides (LPS), and to Staphylococcus aureus and its peptidoglycans, depending on Ca(2+). In addition, the Intl-3 protein agglutinated E. coli cells in the presence of Ca(2+). Intraperitoneal injection of LPS increased the intestinal and rectal contents of Intl-3 and XCL-1 (or 35K serum lectin) proteins within three days; however, unlike XCL-1, Intl-3 was detectable in neither the sera nor the other tissues regardless of LPS stimulation. Immunohistochemical analyses revealed accumulation of the Intl-3 protein in mucus secretory granules of intestinal goblet cells. The results of this study suggest that Xenopus Intl-3 is involved in the innate immune protection of the digestive tract against bacterial infections.

Structures of Xenopus Embryonic Epidermal Lectin Reveal a Conserved Mechanism of Microbial Glycan Recognition

Intelectins (X-type lectins), broadly distributed throughout chordates, have been implicated in innate immunity. Xenopus laevis embryonic epidermal lectin (XEEL), an intelectin secreted into environmental water by the X. laevis embryo, is postulated to function as a defense against microbes. XEEL is homologous (64% identical) to human intelectin-1 (hIntL-1), which is also implicated in innate immune defense. We showed previously that hIntL-1 binds microbial glycans bearing exocyclic vicinal diol groups. It is unknown whether XEEL has the same ligand specificity. Also unclear is whether XEEL and hIntL-1 have similar quaternary structures, as XEEL lacks the corresponding cysteine residues in hIntL-1 that stabilize the disulfide-linked trimer. These observations prompted us to further characterize XEEL. We found that hIntL-1 and XEEL have similar structural features. Even without the corresponding intermolecular disulfide bonds present in hIntL-1, the carbohydrate recognition domain of XEEL (XEELCRD) forms a stable trimer in solution. The structure of XEELCRD in complex with d-glycerol-1-phosphate, a residue present in microbe-specific glycans, indicated that the exocyclic vicinal diol coordinates to a protein-bound calcium ion. This ligand-binding mode is conserved between XEEL and hIntL-1. The domain architecture of full-length XEEL is reminiscent of a barbell, with two sets of three glycan-binding sites oriented in opposite directions. This orientation is consistent with our observation that XEEL can promote the agglutination of specific serotypes of Streptococcus pneumoniae. These data support a role for XEEL in innate immunity, and they highlight structural and functional conservation of X-type lectins among chordates.

Grass carp SARM1 and its two splice variants negatively regulate IFN-I response and promote cell death upon GCRV infection at different subcellular locations

Sterile alpha and Toll/IL-1R motif containing 1 (SARM1) negatively regulates TRIF-dependent TLR signaling in mammals. However, its immune function remains unclear in teleost. Here, a grass carp Ctenopharyngodon idella SARM1 (CiSARM1) gene and its two novel splice variants (CiSARM1s1 and CiSARM1s2) were identified. CiSARM1s1 and CiSARM1s2 are generated by intron retention mechanism, and they only retain N-terminal HEAT/armadillo motifs. In C. idella kidney (CIK) cells, CiSARM1 and CiSARM1s1 are located in mitochondria, whereas CiSARM1s2 distributes in the whole cell. All the three transcripts are ubiquitously expressed in 15 investigated tissues. They were responsive to GCRV in vivo and in vitro and to viral/bacterial PAMPs in vitro, implying they participate in both antiviral and antibacterial immune responses. By overexpression experiment, CiSARM1 and its two isoforms affected each other's expression in CIK cells. CiSARM1 inhibited GCRV-triggered IFN-I response by affecting the expressions of CiTRIF, CiMyD88, CiIPS-1, CiTRAF6, CiTBK1, CiIRF3 and CiIRF7 in TRIF-, MyD88- and IPS-1-dependent pathways; CiSARM1s1 and CiSARM1s2 inhibited GCRV-triggered IFN-I production through suppressing the expressions of CiMyD88, CiIPS-1, CiTRAF6, CiTBK1, CiIRF3 and CiIRF7 in MyD88- and IPS-1-dependent pathways. Moreover, antiviral activity assays indicated that all the three genes promote GCRV-induced cell death. These results were further verified by RNAi experiments. Thus, CiSARM1 and its two splice variants jointly prevent excessive activation of the host immune response. These findings uncover the regulatory mechanisms of SARM1 in teleost and lay a foundation for further functional and evolutionary researches on SARM1.

Preparation, identfication, and activity assay of lamprey (lampetra japonica) natural intelectins

Intelectins play an important role in innate immune response. In a previous study, lamprey inteletins purified by galactose-Sepharose were inactive and insoluble. Herein, we provided a simple and effective method to purify natural intelectins from the serum of lamprey (Lethenteron japonicum) using proteinG agarose. SDS-PAGE, two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), and mass spectrometry (MS) were used to analyze the purified proteins. The purified proteins were identified to be lamprey serum lectin and intelectinB. The activity analysis results indicated that the proteins had certain extent agglutination activity. The effective method will be useful to study their immune functions and molecular mechanisms.

First evidence of protein G-binding protein in the most primitive vertebrate: serum lectin from lamprey (Lampetra japonica)

The intelectins, a recently identified subgroup of extracellular animal lectins, are glycan-binding receptors that recognize glycan epitopes on foreign pathogens in host systems. Here, we have described NPGBP (novel protein G-binding protein), a novel serum lectin found in the lamprey, Lampetra japonica. RT-PCR yielded a 1005 bp cDNA sequence from the lamprey liver encoding a 334 amino acid secretory protein with homology to mammalian and aquatic organism intelectins. Gene expression analyses showed that the NPGBP gene was expressed in the blood, intestines, kidney, heart, gill, liver, adipose tissue and gonads. NPGBP was isolated by protein G-conjugated agarose immunoprecipitation, and SDS-PAGE analyses showed that NPGBP migrated as a specific band (∼35 and ∼124 kDa under reducing and non-reducing conditions, respectively). These results suggested that NPGBP forms monomers and tetramers. NPGBP gene expression was induced by in vivo bacterial stimulation, and NPGBP showed different agglutination activities against pathogenic Gram-positive bacteria, Gram-negative bacteria and fungi. The induction of NPGBP suggested that it plays an important role in defense against microorganisms in the internal circulation system of the lamprey. When incubated with an unrelated antibody, the specific binding between NPGBP and protein G was competitively inhibited, indicating that NPGBP and the Fc region of Ig bind to the same site on protein G. We thus assume that the tertiary structure of NPGBP is similar to that of the Fc region of Ig. Additionally, NPGBP can effectively promote endothelial cell mitosis. These findings suggest that NPGBP plays a role in the immune defense against microorganisms, and this study represents one of the few examples of the characterization and functional analysis of an aquatic organism intelectin.

Comparative genomic and phylogenetic analyses of the intelectin gene family: implications for their origin and evolution

Intelectin is a newly characterized gene family involved in early embryogenesis, host-pathogen interactions and iron metabolism. In this study, we searched the genomes of metazoans by extensive BLAST survey and found no intelectin homologs in invertebrate metazoans but 12 in amphioxus Branchiostoma floridae and 21 in ascidians Ciona intestinalis. Some ascidians oocyte cortical granule lectins (CGLs) have unknown insertion sequences between fibrinogen-related domain (FReD) and Intelectin Domain, the boundaries of which are equivalent to exon structures. In addition to ascidians intelectins/CGLs located in the base, phylogenetic tree comprises four main clades representing mammal, frog, fish, and amphioxus, indicating that intelectin genes undergo extensive lineage-specific duplication or gene conversion. However, genomic neighborhood surrounding analysis shows that clear proto-orthologies are difficult to be established among these counterparts. In addition, sequence comparison and phylogenetic analysis of FReDs from intelectins and other fibrinogen-like proteins from choanoflagellate, anemone, frog and human indicate FReDs of intelectins are unique. Likewise, these choanoflagellate and anemone genes may be close to intelectin gene.

Characterization and comparative analyses of two amphioxus intelectins involved in the innate immune response

Intelectin is a new type of soluble galactofuranose-binding lectin involved in innate immunity. Here we report another intelectin homolog, AmphiITLN239631, obtained from amphioxus, the transitional form between vertebrates and invertebrates. AmphiITLN239631 encoded 396 amino acids with a highly conserved fibrinogen-related domain (FReD), An intelectin domain and a putative Collagen domain. AmphiITLN239631 was ubiquitously expressed in all tissues we tested and transcripts in skin increased after challenge of both Escherichia coli and Staphylococcus aureus, although in different levels. Recombinant AmphiITLN239631 expressed in E. coli system could agglutinate both Gram-positive and Gram-negative bacteria in a calcium independent manner. Furthermore, recombinant protein was able to bind to lipopolysaccharide (LPS) and peptidoglycan (PGN), the major components of Gram-positive and Gram-negative bacteria cell walls, respectively. We also compared AmphiITLN239631 with previously identified AmphiITLN71469 and found that their tissue specificities, expression patterns upon bacteria challenge, and polysaccharide-binding affinities etc vary considerably. Our results could provide insight into the evolution and function of the intelectin family.

The interaction between maternal stress and the ontogeny of the innate immune system during teleost embryogenesis: implications for aquaculture practice

The barrier defences and acellular innate immune proteins play critical roles during the early-stage fish embryos prior to the development of functional organ systems. The innate immune proteins in the yolk of embryos are of maternal origin. Maternal stress affects the maternal-to-embryo transfer of these proteins and, therefore, environmental stressors may change the course of embryo development, including embryonic immunocompetency, via their deleterious effect on maternal physiology. This review focuses on the associations that exist between maternal stress, maternal endocrine disturbance and the responses of the acellular innate immune proteins of early-stage fish embryos. Early-stage teleostean embryos are dependent upon the adult female for the formation of the zona pellucida as an essential barrier defence, for their supply of nutrients, and for the innate immunity proteins and antibodies that are transferred from the maternal circulation to the oocytes; maternally derived hormones are also transferred, some of which (such as cortisol) are known to exert a suppressive action on some aspects of the immune defences. This review summarizes what is known about the effects of oocyte cortisol content on the immune system components in early embryos. The review also examines recent evidence that embryonic cells during early cleavage have the capacity to respond to increased maternal cortisol transfer; this emphasizes the importance of maternal and early immune competence on the later life of fishes, both in the wild and in intensive culture.

Identification of an amphioxus intelectin homolog that preferably agglutinates gram-positive over gram-negative bacteria likely due to different binding capacity to LPS and PGN

Intelectin is a recently described galactofuranose-binding lectin that plays a role in innate immunity in vertebrates. Little is known about intelectin in invertebrates, including amphioxus, the transitional form between vertebrates and invertebrates. We cloned an amphioxus intelectin homolog, AmphiITLN-like, coding 302 amino acids with a conserved fibrinogen-related domain (FReD) in the N-terminus and an Intelectin domain in the C-terminus. In situ hybridization in adult amphioxus showed that AmphiITLN-like transcripts were highly expressed in the digestive tract and the skin. Quantitative real-time PCR revealed that AmphiITLN-like is significantly up-regulated in response to Staphylococcus aureus challenge, but only modestly to Escherichia coli. In addition, recombinant AmphiITLN-like expressed in E. coli agglutinates Gram-negative and Gram-positive bacteria to different degrees in a calcium dependent manner. Recombinant AmphiITLN-like could bind lipopolysaccharide (LPS) and peptidoglycan (PGN), the major cell wall components of Gram-negative and Gram-positive bacteria, respectively, with a higher affinity to PGN. Our work identified and characterized for the first time an amphioxus intelectin homolog, and provided insight into the evolution and function of the intelectin family.

Lipopolysaccharide O-antigen prevents phagocytosis of Vibrio anguillarum by rainbow trout (Oncorhynchus mykiss) skin epithelial cells

Colonization of host tissues is a first step taken by many pathogens during the initial stages of infection. Despite the impact of bacterial disease on wild and farmed fish, only a few direct studies have characterized bacterial factors required for colonization of fish tissues. In this study, using live-cell and confocal microscopy, rainbow trout skin epithelial cells, the main structural component of the skin epidermis, were demonstrated to phagocytize bacteria. Mutant analyses showed that the fish pathogen Vibrio anguillarum required the lipopolysaccharide O-antigen to evade phagocytosis and that O-antigen transport required the putative wzm-wzt-wbhA operon, which encodes two ABC polysaccharide transporter proteins and a methyltransferase. Pretreatment of the epithelial cells with mannose prevented phagocytosis of V. anguillarum suggesting that a mannose receptor is involved in the uptake process. In addition, the O-antigen transport mutants could not colonize the skin but they did colonize the intestines of rainbow trout. The O-antigen polysaccharides were also shown to aid resistance to the antimicrobial factors, lysozyme and polymyxin B. In summary, rainbow trout skin epithelial cells play a role in the fish innate immunity by clearing bacteria from the skin epidermis. In defense, V. anguillarum utilizes O-antigen polysaccharides to evade phagocytosis by the epithelial cells allowing it to colonize rapidly fish skin tissues.

Isolation and determination of the primary structure of a lectin protein from the serum of the American alligator (Alligator mississippiensis)

Mass spectrometry in conjunction with de novo sequencing was used to determine the amino acid sequence of a 35kDa lectin protein isolated from the serum of the American alligator that exhibits binding to mannose. The protein N-terminal sequence was determined using Edman degradation and enzymatic digestion with different proteases was used to generate peptide fragments for analysis by liquid chromatography tandem mass spectrometry (LC MS/MS). Separate analysis of the protein digests with multiple enzymes enhanced the protein sequence coverage. De novo sequencing was accomplished using MASCOT Distiller and PEAKS software and the sequences were searched against the NCBI database using MASCOT and BLAST to identify homologous peptides. MS analysis of the intact protein indicated that it is present primarily as monomer and dimer in vitro. The isolated 35kDa protein was ~98% sequenced and found to have 313 amino acids and nine cysteine residues and was identified as an alligator lectin. The alligator lectin sequence was aligned with other lectin sequences using DIALIGN and ClustalW software and was found to exhibit 58% and 59% similarity to both human and mouse intelectin-1. The alligator lectin exhibited strong binding affinities toward mannan and mannose as compared to other tested carbohydrates.

Zebrafish (Danio rerio) as a screen for attenuation of Lancefield group C streptococci and a model for streptococcal pathogenesis

Group C streptococci are highly contagious pyogenic bacteria responsible for respiratory tract, lymph node, urogenital tract, and wound infections. Wild-type strains of Streptococcus equi ssp equi (S. equi) and Streptococcus equi ssp zooepidemicus (S. zoo) as well as a commercially available modified live vaccine strain of S. equi were evaluated for virulence in zebrafish. Survival times, histologic lesions, and relative gene expression were compared among groups. Based on the intramuscular route of infection, significantly shorter survival times were observed in fish infected with wild-type strain when compared to modified live vaccine and S. zoo strains. Histologically, S. zoo-infected fish demonstrated a marked increase in inflammatory infiltrates (predominantly macrophages) at the site of infection, as well as increased cellularity in the spleen and renal interstitium. In contrast, minimal cellular immune response was observed in S. equi-injected fish with local tissue necrosis and edema predominating. Based on whole comparative genomic hybridization, increased transcription of positive acute-phase proteins, coagulation factors, and antimicrobial peptides were observed in S. equi-injected fish relative to S. zoo-injected fish, while mediators of cellular inflammation, including CXC chemokines and granulin, were upregulated in S. zoo-injected fish relative to S. equi-injected fish. In a screen of 11 clinical isolates, S. equi strains with a single nucleotide deletion in the upstream region of szp, a known virulence factor of streptococci, were found to be significantly attenuated in zebrafish. These collective findings underscore the value of the zebrafish as a model of streptococcal pathogenesis.

The influence of oocyte cortisol on the early ontogeny of intelectin and TLR-5, and changes in lysozyme activity in rainbow trout (Oncorhynchus mykiss) embryos

The ontogeny of lysozyme activity, intelectin, TLR-5M and TLR-5S gene expression and intelectin localization was examined in rainbow trout (Oncorhynchus mykiss) reared from oocytes immersed for 3h prior to fertilization in either ovarian fluid alone (CC) or cortisol-enriched ovarian fluid at either 100 ng mL(-1) (C1) or 1000 ng mL(-1) (C2) [final oocyte cortisol concentrations were ~3, ~5, and ~7.5 ng oocyte(-1) for the CC, C1 and C2 treatment groups, respectively]. Lysozyme activity was elevated in the cortisol-treated groups from the zygote until 13-days post fertilization (dpf), but was not affected at 21-dpf. Intelectin levels were elevated in both cortisol treatment groups at 12-hpf (2-cell stage) and then suppressed between 36- and 48-hpf. Intelectin mRNA transcript levels were elevated in both cortisol treatment groups in oocytes; there were no differences among treatment groups at 1- and 5-dpf, and suppressed in the C2 treatment group in 13-dpf and 26-dpf. TLR-5 mRNA transcripts were higher in cortisol-treated oocytes prior to fertilization; TLR-5S mRNA was more abundant than TLR-5M mRNA. The ontogeny of the gene expression patterns, and the gene, lectin and lysozyme responses to oocyte cortisol adjustments suggest an important role of innate immune systems in the early cleavage stages of embryonic cells.

Rainbow trout Oncorhynchus mykiss ladderlectin, but not intelectin, binds viral hemorrhagic septicemia virus IVb

The innate immune system of fish is critical for rapid detection and immediate response to infection, as well as to orchestrate the adaptive branch of the immune system. Rainbow trout Oncorhynchus mykiss ladderlectin and intelectin are plasma pattern recognition receptors (PRR) for bacterial and fungal pathogens of rainbow trout, but their role as PRRs for virus is unknown. Viral hemorrhagic septicemia virus (VHSV) IVb is a recently described fish pathogen in the Great Lakes, and rainbow trout can be experimentally infected. Using an indirect enzyme-linked immunosorbent assay, rainbow trout plasma ladderlectin significantly (p < 0.05) bound purified VHSV while intelectin did not. In addition, plasma ladderlectin but not intelectin was eluted from a VHSV-conjugated Toyopearl column using EDTA. Protein identification was confirmed with polyclonal antiserum used with slot immunoblot, 1-dimensional sodium dodecyl sulphate polyacrylamide electrophoresis, and Western immunoblot.

Expression of three intelectins in sheep and response to a Th2 environment

Sheep intelectin1 and sheep intelectin3 (sITLN1 and sITLN3) were cloned and sequenced. The amino acid sequences of sITLN1 and sITLN3 shared 86% and 91% homology with the previously cloned sheep intelectin2 (sITLN2), respectively. Expression of sITLN1 and sITLN3 transcript was demonstrated in abomasum, lung, colon and gastric lymph node, terminal rectum, skin, jejunum, mesenteric lymph node, ileal peyer’s patches, brain, kidney, liver, spleen, skin, ear pinna, heart and ovary in normal sheep tissues. sITLN2 transcript expression was restricted to the abomasal mucosa in normal sheep tissues. Using a non selective chicken anti-intelectin antibody, tissue intelectin protein was demonstrated in mucus neck cells in the abomasum, mucus cells in the colon, free mucus in ileum, goblet cells in the lung, small intestinal epithelium and brush border, epidermal layer of the skin and skin sebaceous glands. The expression of the three sITLN transcripts was examined in two nematode infections in sheep known to induce a Th2 response; a Teladorsagia circumcincta challenge infection model and a Dictyocaulus filaria natural infection. The three sITLN were absent in unchallenged naïve lambs and present in the abomasal mucosa of both naïve and immune lambs following T. circumcincta challenge infection. Upregulation of sITLN2 and sITLN3 was shown in sheep lung following D. filaria natural infection. Intelectins may play an important role in the mucosal response to nematode infections in ruminants.

Characterization and comparative analyses of zebrafish intelectins: highly conserved sequences, diversified structures and functions

Intelectin family, also called the X-lectin family, is a newly discovered gene family involved in development and innate immunity. However, no research was carried out for this gene family in the model organism zebrafish. Here we present the first characterization of seven zebrafish intelectins (zINTLs) and the first systematic comparative analysis of intelectins from various species in order to provide some clues to the function and evolution of this gene family. We examined the expression patterns of zINTLs in various development stages, normal adults, and Aeromonas salmonicida infected adults. Results showed that zINTL1-3 were highly expressed in one or several adult tissues. zINTL4-7, however, were expressed at quite low levels both in adults and various development stages, and some of them showed relaxation of functional constrains as revealed by K(a)/K(s) calculation. Of the seven zINTLs, zINTL3 was expressed predominantly in the liver and highly up-regulated upon infection, suggesting its important roles in immunity. Based on the characterization of zebrafish intelectins, we then conducted a systematic survey of intelectin members in various species and made comparative analyses. We found out that intelectin family may be a deuterostome specific gene family; and their expression patterns, quaternary structures and glycosylations vary considerably among various species, though their sequences are highly conserved. Moreover, these varied features have evolved multiple times independently in different species, resulting in species-specific protein structures and expression patterns.

Capture of heat-killed Mycobacterium bovis bacillus Calmette-Guérin by intelectin-1 deposited on cell surfaces

Intelectin is an extracellular animal lectin found in chordata. Although human and mouse intelectin-1 recognize galactofuranosyl residues included in cell walls of various microorganisms, the physiological function of mammalian intelectin had been unclear. In this study, we found that human intelectin-1 was a serum protein and bound to Mycobacterium bovis bacillus Calmette-Guérin (BCG). Human intelectin-1-binding to BCG was inhibited by Ca(2+)-depletion, galactofuranosyl disaccharide, ribose, or xylose, and was dependent on the trimeric structure of human intelectin-1. Although monomeric, mouse intelectin-1 bound to BCG, with its C-terminal region contributing to efficient binding. Human intelectin-1-transfected cells not only secreted intelectin-1 into culture supernatant but also expressed intelectin-1 on the cell surface. The cell surface intelectin-1 was not a glycosylphosphatidylinositol-anchored membrane protein. Intelectin-1-transfected cells captured BCG more than untransfected cells, and the BCG adherence was inhibited by an inhibitory saccharide of intelectin-1. Intelectin-1-preincubated cells took up BCG more than untreated cells, but the adhesion of intelectin-1-bound BCG was the same as that of untreated BCG. Mouse macrophages phagocytosed BCG more efficiently in medium containing mouse intelectin-1 than in control medium. These results indicate that intelectin is a host defense lectin that assists phagocytic clearance of microorganisms.