title: Deletion of a CD2-like gene, 8-DR, from African swine fever virus affects viral infection in domestic swine.
abstract: An African swine fever virus (ASFV) gene with similarity to the T-lymphocyte surface antigen CD2 has been found in the pathogenic African isolate Malawi Lil-20/1 (open reading frame [ORF] 8-DR) and a cell culture-adapted European virus, BA71V (ORF EP402R) and has been shown to be responsible for the hemadsorption phenomenon observed for ASFV-infected cells. The structural and functional similarities of the ASFV gene product to CD2, a cellular protein involved in cell-cell adhesion and T-cell-mediated immune responses, suggested a possible role for this gene in tissue tropism and/or immune evasion in the swine host. In this study, we constructed an ASFV 8-DR gene deletion mutant (delta8-DR) and its revertant (8-DR.R) from the Malawi Lil-20/1 isolate to examine gene function in vivo. In vitro, delta8-DR, 8-DR.R, and the parental virus exhibited indistinguishable growth characteristics on primary porcine macrophage cell cultures. In vivo, 8-DR had no obvious effect on viral virulence in domestic pigs; disease onset, disease course, and mortality were similar for the mutant delta8-DR, its revertant 8-DR.R, and the parental virus. Altered viral infection was, however, observed for pigs infected with delta8-DR. A delay in spread to and/or replication of delta8-DR in the draining lymph node, a delay in generalization of infection, and a 100- to 1,000-fold reduction in virus titers in lymphoid tissue and bone marrow were observed. Onset of viremia for delta8-DR-infected animals was significantly delayed (by 2 to 5 days), and mean viremia titers were reduced approximately 10,000-fold at 5 days postinfection and 30- to 100-fold at later times; moreover, unlike in 8-DR.R-infected animals, the viremia was no longer predominantly erythrocyte associated but rather was equally distributed among erythrocyte, leukocyte, and plasma fractions. Mitogen-dependent lymphocyte proliferation of swine peripheral blood mononuclear cells in vitro was reduced by 90 to 95% following infection with 8-DR.R but remained unaltered following infection with delta8-DR, suggesting that 8-DR has immunosuppressive activity in vitro. Together, these results suggest an immunosuppressive role for 8-DR in the swine host which facilitates early events in viral infection. This may be of most significance for ASFV infection of its highly adapted natural host, the warthog.
authors.affiliation: Plum Island Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture, Greenport, New York 11944-0848, USA.
authors.forename: M V
authors.initials: MV
authors.lastname: Borca
authors.forename: C
authors.initials: C
authors.lastname: Carrillo
authors.forename: L
authors.initials: L
authors.lastname: Zsak
authors.forename: W W
authors.initials: WW
authors.lastname: Laegreid
authors.forename: G F
authors.initials: GF
authors.lastname: Kutish
authors.forename: J G
authors.initials: JG
authors.lastname: Neilan
authors.forename: T G
authors.initials: TG
authors.lastname: Burrage
authors.forename: D L
authors.initials: DL
authors.lastname: Rock
mesh_terms: D000357:African Swine Fever / Q000473:pathology / Q000821:virology*; D000358:African Swine Fever Virus / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity / Q000502:physiology*; D000818:Animals; D018801:CD2 Antigens / Q000737:chemistry; D002455:Cell Division; D002478:Cells, Cultured; D003001:Cloning, Molecular; D017353:Gene Deletion; D005814:Genes, Viral; D007963:Leukocytes, Mononuclear; D008214:Lymphocytes / Q000187:drug effects / Q000821:virology; D008264:Macrophages / Q000166:cytology / Q000821:virology; D008934:Mitogens / Q000494:pharmacology; D013552:Swine; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology*
chemical_list: D018801:CD2 Antigens; D008934:Mitogens; D014764:Viral Proteins