Bacterial lipopolysaccharides stimulate production of XCL1, a calcium-dependent lipopolysaccharide-binding serum lectin, in Xenopus laevis

Seroprevalence of infectious bursal disease and its associated risk factors in Ethiopia: a systematic review and meta-analysis

The poultry population is an integral part of Ethiopia's Gross Domestic Product (GDP) but, due to various infectious diseases such as infectious bursal disease (IBD), the expected economic impact in the country remains limited. The status of the disease in Ethiopia is obscured; thus, a systematic review and meta-analysis were employed to estimate the overall pooled prevalence of IBD in Ethiopia. Meta-analysis was conducted to determine the effects of each identified risk factor, while meta-regression and sub-group analysis were employed to assess the relationship between study-level covariates and effect size. The pooled prevalence of IBD in Ethiopia was 69.4% (95% CI 30.7-96.2), while the pooled logit prevalence was 0.94 (95% CI: 0.68-1.20) with significant inter-study variance (Q test = 948.28, df = 43, P < 0.001; τ2 = 0.71, I2 = 95.47%). A small-study effect was detected in the regression-based Egger test (Prob > |z| < 0.0001). Significant variation was observed among different groups such as sex, age, breed, and type of farm of the chickens. The effect size for the study period from 2018 to 2021 was significantly lower by -0.204 compared to the study period from 2009 to 2015 (P < 0.0001. In conclusion, the IBD pooled prevalence estimate is high, even though the number of studies in the country is insufficient. The high prevalence of the disease requires prompt attention from all stakeholders in the sector to bring it under control through comprehensive disease prevention and control intervention strategies.

Potential Involvement of the South American Lungfish Intelectin-2 in Innate-Associated Immune Modulation

Intelectins belong to a family of lectins with specific and transitory carbohydrate interaction capabilities. These interactions are related to the activity of agglutinating pathogens, as intelectins play a significant role in immunity. Despite the prominent immune defense function of intelectins, limited information about its structural characteristics and carbohydrate interaction properties is available. This study investigated an intelectin transcript identified in RNA-seq data obtained from the South American lungfish (Lepidosiren paradoxa), namely LpITLN2-B. The structural analyses predicted LpITLN2-B to be a homo-trimeric globular protein with the fibrinogen-like functional domain (FReD), exhibiting a molecular mass of 57 kDa. The quaternary structure is subdivided into three monomers, A, B, and C, and each domain comprises 11 β-sheets: an anti-parallel β-sheet, a β-hairpin, and a disordered β-sheet structure. Molecular docking demonstrates a significant interaction with disaccharides rather than monosaccharides. The preferential interaction with disaccharides highlights the potential interaction with pathogen molecules, such as LPS and Poly(I:C). The hemagglutination assay inhibited lectins activity, especially maltose and sucrose, highlighting lectin activity in L. paradoxa samples. Overall, our results show the potential relevance of LpITLN2-B in L. paradoxa immune defense against pathogens.

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.

Embryonic Epidermal Lectins in Three Amphibian Species, Rana ornativentris, Bufo japonicus formosus, and Cynops pyrrhogaster

Intelectins (Itlns) are secretory lectins found in several chordate species that recognize carbohydrates on the bacterial cell surface depending on Ca^{2 +} . In newly hatched larvae of Rana ornativentris (R. orn), Bufo japonicus formosus (B. jpn), and Cynops pyrrhogaster (C. pyr), an anti-Itln monoclonal antibody (mAb) labeled a subset of epidermal cells in whole-mount immunocytochemical assays. In western blot analyses, the mAb identified protein bands at approximately 33-37 kDa in the larval extracts and concentrated larval culture media. Using RT-PCR and RACE techniques, we isolated cDNAs from newly hatched larvae that encoded proteins of 343 (R. orn), 336 (B. jpn), and 337 (C. pyr) amino acids having 70%, 71%, and 60% identities with that of the Xenopus laevis embryonic epidermal lectin (XEEL), respectively. The proteins, designated REEL, BEEL, and CEEL, showed characteristics conserved among reported Itln proteins, and their amino acid sequences following the signal peptides were identical to those of the N-terminal peptides determined on Itln proteins in the respective larval extracts. Recombinant REEL (rREEL), rBEEL, and rCEEL proteins produced by HEK-293T cells were homo-oligomers of 34-37 kDa subunit peptides, which were similar to the Itlns found in the newly hatched larvae. The rEELs showed carbohydrate-binding specificities similar to that of XEEL and agglutinated Escherichia coli and Staphylococcus aureus cells depending on Ca^{2 +} . These results suggest that REEL, BEEL, and CEEL are Itlns produced and secreted by epidermal cells of R. orn, B. jpn, and C. pyr larvae, respectively, and that Itlns have a conserved role as pathogen recognition molecules in the larval innate immune system.

Diepoxybutane induces the expression of a novel p53-target gene XCL1 that mediates apoptosis in exposed human lymphoblasts

Diepoxybutane (DEB) is the most potent active metabolite of the environmental chemical 1,3-butadiene (BD). BD is a human carcinogen that exhibits multiorgan systems toxicity. Our previous studies demonstrated that the X-C motif chemokine ligand 1 (XCL1) gene expression was upregulated 3.3-fold in a p53-dependent manner in TK6 lymphoblasts undergoing DEB-induced apoptosis. The tumor-suppressor p53 protein is a transcription factor that regulates a wide variety of cellular processes, including apoptosis, through its various target genes. Thus, the objective of this study was to determine whether XCL1 is a novel direct p53 transcriptional target gene and deduce its role in DEB-induced toxicity in human lymphoblasts. We utilized the bioinformatics tool p53scan to search for known p53 consensus sequences within the XCL1 promoter region. The XCL1 gene promoter region was found to contain the p53 consensus sequences 5'-AGACATGCCTAGACATGCCT-3' at three positions relative to the transcription start site (TSS). Furthermore, the XCL1 promoter region was found, through reporter gene assays, to be transactivated at least threefold by wild-type p53 promoter in DEB-exposed human lymphoblasts. Inactivation of the XCL1 promoter p53-binding motif located at -2.579 kb relative to TSS reduced the transactivation function of p53 on this promoter in DEB-exposed cells by 97%. Finally, knockdown of XCL1 messenger RNA with specific small interfering RNA inhibited DEB-induced apoptosis in human lymphoblasts by 50%. These observations demonstrate, for the first time, that XCL1 is a novel DEB-induced direct p53 transcriptional target gene that mediates apoptosis in DEB-exposed human lymphoblasts.

Xenopus laevis macrophage-like cells produce XCL-1, an intelectin family serum lectin that recognizes bacteria

Xenopus laevis Ca²⁺ -dependent lectin-1 (XCL-1) is an intelectin family serum lectin that selectively recognizes carbohydrate chains on the bacterial cell surface. Immunofluorescence examination of control spleen tissues from normal X. laevis revealed cells producing XCL-1 (XCL-1⁺ cells) exclusively in red pulps. Intraperitoneal injection of Escherichia coli lipopolysaccharide (LPS) caused a marked increase in the number of XCL-1⁺ cells in red pulps on day 3, followed by a rapid decrease to near control levels by day 7. XCL-1⁺ cells were also detected in peripheral blood leukocytes (PBLs) and peritoneal exudate cells (PECs), and their numbers increased upon LPS injection until day 7. The XCL-1⁺ cells exhibited the morphological characteristics of macrophages, with a large oval or lobulated nucleus and abundant cytoplasm with vacuoles and dendritic projections. Western blot analyses revealed concurrent increases in XCL-1 levels in the spleen, PBLs, and PECs. When LPS-stimulated frogs were intraperitoneally injected with paraformaldehyde-fixed, green fluorescent protein-labeled E. coli cells (GFP-Eco), these were phagocytosed by XCL-1⁺ PECs. The purified XCL-1 protein agglutinated GFP-Eco in a Ca²⁺ -dependent manner, which was blocked effectively by xylose and partly by LPS and Staphylococcus aureus peptidoglycan, but not by sucrose. These results indicate that X. laevis macrophage-like cells produce XCL-1 and suggest that XCL-1 promotes the clearance of invaded bacteria by facilitating phagocytosis.

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.

Urotensin II upregulates migration and cytokine gene expression in leukocytes of the African clawed frog, Xenopus laevis

Urotensin II (UII) exhibits diverse physiological actions including vasoconstriction, locomotor activity, osmoregulation, and immune response via the UII receptor (UTR) in mammals. However, in amphibians the function of the UII-UTR system remains unknown. In the present study, we investigated the potential immune function of UII using leukocytes isolated from the African clawed frog, Xenopus laevis. Stimulation of male frogs with lipopolysaccharide increased mRNA expression of UII and UTR in leukocytes, suggesting that inflammatory stimuli induce activation of the UII-UTR system. Migration assays showed that both UII and UII-related peptide enhanced migration of leukocytes in a dose-dependent manner, and that UII effect was inhibited by the UTR antagonist urantide. Inhibition of Rho kinase with Y-27632 abolished UII-induced migration, suggesting that it depends on the activation of RhoA/Rho kinase. Treatment of isolated leukocytes with UII increased the expression of several cytokine genes including tumor necrosis factor-α, interleukin-1β, and macrophage migration inhibitory factor, and the effects were abolished by urantide. These results suggest that in amphibian leukocytes the UII-UTR system is involved in the activation of leukocyte migration and cytokine gene expression in response to inflammatory stimuli.