title: Orf virus-encoded interleukin-10 stimulates the proliferation of murine mast cells and inhibits cytokine synthesis in murine peritoneal macrophages.
abstract: Orf virus (ORFV) is the type species of the parapoxvirus genus and produces cutaneous pustular lesions in sheep, goats and humans. The genome encodes a polypeptide with remarkable homology to interleukin-10 (IL-10), particularly ovine IL-10, and also to IL-10-like proteins encoded by Epstein-Barr virus (EBV) and equine herpesvirus. IL-10 is a pleiotropic cytokine that can exert either immunostimulatory or immunosuppressive effects on many cell types. We have expressed and purified C-terminal FLAG and His(6)-tagged versions of ORFV-IL-10 and shown that ORFV-IL-10 costimulates murine mast cells (MC/9) and inhibits tumour necrosis factor-alpha synthesis in activated mouse peritoneal macrophages. Our results demonstrate that although ORFV-IL-10 is structurally similar to EBV-IL-10 it has evolved a different spectrum of activities. EBV-IL-10 does not stimulate the proliferation of thymocytes or mast cells whereas ORFV-IL-10 has both of these activities. Recent studies show that the critical difference in molecular structure of human IL-10 and EBV-IL-10, which may be the basis of their functional differences, is linked to a single amino acid substitution. Consistent with the activity spectrum reported here for ORFV-IL-10, the viral gene encodes the critical amino acid seen in human IL-10. Although the ORFV-IL-10 gene has clearly undergone significant evolutionary change at the nucleotide level compared with ovine IL-10, it has largely retained the polypeptide structure and functional characteristics of its ovine counterpart, suggesting that mutations of the gene to a potentially more potent immunosuppressive form may compromise the co-existence of host and virus.
authors.affiliation: Virus Research Unit and Centre for Gene Research, Department of Microbiology, University of Otago, PO Box 56, Dunedin, New Zealand1.
authors.forename: Wendy
authors.initials: W
authors.lastname: Imlach
authors.affiliation: Virus Research Unit and Centre for Gene Research, Department of Microbiology, University of Otago, PO Box 56, Dunedin, New Zealand1.
authors.forename: Catherine A
authors.initials: CA
authors.lastname: McCaughan
authors.affiliation: Virus Research Unit and Centre for Gene Research, Department of Microbiology, University of Otago, PO Box 56, Dunedin, New Zealand1.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Mercer
authors.affiliation: The Moredun Research Institute, International Research Centre, Pentland Science Park, Penicuik EH26 OPZ, UK2.
authors.forename: David
authors.initials: D
authors.lastname: Haig
authors.affiliation: Virus Research Unit and Centre for Gene Research, Department of Microbiology, University of Otago, PO Box 56, Dunedin, New Zealand1.
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Fleming
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D016753:Interleukin-10 / Q000096:biosynthesis / Q000737:chemistry / Q000494:pharmacology*; D017737:Macrophages, Peritoneal / Q000187:drug effects* / Q000378:metabolism; D008407:Mast Cells / Q000187:drug effects* / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009923:Orf virus / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis*; D014764:Viral Proteins / Q000494:pharmacology*
chemical_list: D014409:Tumor Necrosis Factor-alpha; D014764:Viral Proteins; D016753:Interleukin-10