Orf virus-encoded interleukin-10 stimulates the proliferation of murine mast cells and inhibits cytokine synthesis in murine peritoneal macrophages.
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.
Imlach
Wendy
W
Virus Research Unit and Centre for Gene Research, Department of Microbiology, University of Otago, PO Box 56, Dunedin, New Zealand1.
McCaughan
Catherine A
CA
Virus Research Unit and Centre for Gene Research, Department of Microbiology, University of Otago, PO Box 56, Dunedin, New Zealand1.
Mercer
Andrew A
AA
Virus Research Unit and Centre for Gene Research, Department of Microbiology, University of Otago, PO Box 56, Dunedin, New Zealand1.
Haig
David
D
The Moredun Research Institute, International Research Centre, Pentland Science Park, Penicuik EH26 OPZ, UK2.
Fleming
Stephen B
SB
Virus Research Unit and Centre for Gene Research, Department of Microbiology, University of Otago, PO Box 56, Dunedin, New Zealand1.
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*
D014409:Tumor Necrosis Factor-alpha; D014764:Viral Proteins; D016753:Interleukin-10