Molecular cloning and characterisation of chicken IL-18 binding protein

• Published in: Developmental and comparative immunology 2021-01, Vol.114, p.103850-103850, Article 103850
• Main Authors: Gibson, Mark S., Steyn, Angela, Kealy, David, Kaspers, Bernd, Fife, Mark S.
• Format: Article
• Language: English
• Subjects: Alternative splicing; Amino acid sequence; Animals; Antiviral agents; Avian Proteins - genetics; Avian Proteins - metabolism; B-Lymphocytes - immunology; Bioactivity; Cell Line; Chicken; Chickens; Chickens - immunology; Cloning; Cloning, Molecular; Cytokines; Divergence; Fowlpox; Fowlpox virus - genetics; Fowlpox virus - metabolism; Gene loci; Gene sequencing; Genetic Loci - genetics; Genetic Vectors - genetics; Genomes; Genomics; Homology; Host-Pathogen Interactions; IL-18 binding protein; Immune response; Immunomodulation; Intercellular Signaling Peptides and Proteins - genetics; Intercellular Signaling Peptides and Proteins - metabolism; Interferon-gamma - metabolism; Interleukin 1; Interleukin 1 receptors; Interleukin 18; Interleukin-18 - metabolism; Intracellular; Lymphocyte Activation; Lymphocytes B; Mammals; Nucleotide sequence; Poultry; Protein Binding; Protein Isoforms - genetics; Proteins; Receptors; Synteny; Vaccines; Vertebrates; Viral Proteins - genetics; Viral Proteins - metabolism; Viruses; γ-Interferon
• ISSN: 0145-305X; 1879-0089
• DOI: 10.1016/j.dci.2020.103850

The human IL-1 receptor family is comprised of 11 membrane bound or soluble receptors and the IL-18 binding protein (IL-18BP). These receptors are dispersed across seven genomic loci, with the majority at a single locus. Direct orthologues were identified in the chicken at conserved genomic loci; however, the IL-18BP remained absent from the first four builds of the chicken genome sequence. Subsequent assemblies identified the gene at a locus syntenic with mammals; however, these predicted sequences differed between genome builds and contained multiple errors. A partial IL-18BP-like sequence in the NCBI EST database was used to clone the full-length cDNA. A splice variant, which lacks the exon that encodes part of the signal peptide, was also cloned. Human IL-18BP is differentially spliced to produce a number of variants, which are all secreted. By contrast, the spliced chicken isoform was predicted to be intracellular, and we identified similar variants with the same exon missing in a limited number of divergent vertebrate species. Mammalian and viral IL-18BPs inhibit IL-18 activity by directly binding to this cytokine. Full-length and intracellular chicken IL-18BPs were equally effective at inhibiting IL-18-mediated IFN-γ release from an avian B-cell line. Analysis of the predicted chIL-18BP protein sequence revealed two crucial residues, which account for 50% of the binding affinity between human IL-18 and IL-18BP, are conserved in the chicken and a fowlpox-encoded homologue, fpv214. This suggests specific fowlpox viruses used in humans as a vaccine vector have the potential to dampen anti-viral host immune responses. •We report the discovery and characterisation of IL-18 binding protein in the chicken.•A spliced intracellular IL-18BP variant was cloned in the chicken.•We identified other vertebrate species that also retain a predicted intracellular IL-18BP isoform.•Both isoforms of chicken IL-18BP are bioactive.