title: Expression of chicken interleukin-2 by a highly virulent strain of Newcastle disease virus leads to decreased systemic viral load but does not significantly affect mortality in chickens.
abstract: BACKGROUND
  In mammals, interleukin 2 (IL-2) has been shown to decrease replication or attenuate pathogenicity of numerous viral pathogens (herpes simplex virus, vaccinia virus, human respiratory syncytial virus, human immunodeficiency virus) by activating natural killer cells (NK), cytotoxic T lymphocytes and expanding subsets of memory cells. In chickens, IL-2 has been shown to activate T cells, and as such it might have the potential to affect replication and pathogenesis of Newcastle disease virus (NDV).
  
  
  METHODS
  To assess the effect of IL-2 during NDV infection in chickens, we produced a recombinant virulent NDV strain expressing chicken IL-2 (rZJ1-IL2). The effects of IL-2 expression were investigated in vivo using the intracerebral pathogenicity index (ICPI) in day-old chicks and pathogenesis experiments in 4-week-old chickens. In these studies, rZJ1-IL2 was compared to a control virus expressing the green fluorescent protein (rZJ1-GFP). Assessed parameters included survival curves, detailed histological and immunohistochemical grading of lesions in multiple organs, and virus isolation in blood, spleen and mucosal secretions of infected birds.
  
  
  RESULTS
  At the site of infection (eyelid), expression of IL-2 was demonstrated in areas of rZJ-IL2 replication, confirming IL-2 production in vivo. Compared to rZJ1-GFP strain, rZJ1-IL2 caused milder lesions and displayed decreased viral load in blood, spleen and mucosal secretions of infected birds. In the rZJ1-IL2-infected group, virus level in the blood peaked at day 4 post-infection (pi) (10(3.46) EID50 /0.1 ml) and drastically decreased at day 5 pi (10(0.9) EID50/0.1 ml), while in the rZJ1-GFP-infected group virus levels in the blood reached 10(5.35) EID50/0.1 ml at day 5. However, rZJ1-IL2-infected groups presented survival curves similar to control birds infected with rZJ1-GFP, with comparable clinical signs and 100 % mortality. Further, expression of IL-2 did not significantly affect the ICPI scores, compared to rZJ1-GFP strain.
  
  
  CONCLUSIONS
  Increased expression of chicken IL-2 during virulent NDV replication in naïve chickens decreased viral titers in blood, spleens, oral and cloacal secretions on day 4-5 post infection. This is consistent with the previously described role of IL-2 in enhancing the clearance of viruses in mammals, such as human respiratory syncytial virus.
authors.affiliation: USDA ARS, Southeast Poultry Research Laboratory, 934 College Station Rd, Athens, GA, 30605, USA. lsusta@uoguelph.ca.|Present address: Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON, N1G 2W1, Canada. lsusta@uoguelph.ca.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Susta
authors.affiliation: USDA ARS, Southeast Poultry Research Laboratory, 934 College Station Rd, Athens, GA, 30605, USA. diego.diel@sdstate.edu.|Present address: Department of Veterinary and Biomedical Sciences, College of Agriculture and Biological Sciences, South Dakota State University, Brookings, SD, 57007, USA. diego.diel@sdstate.edu.
authors.forename: Diego G
authors.initials: DG
authors.lastname: Diel
authors.affiliation: USDA ARS, Southeast Poultry Research Laboratory, 934 College Station Rd, Athens, GA, 30605, USA. courtney_sean@bah.com.
authors.forename: Sean
authors.initials: S
authors.lastname: Courtney
authors.affiliation: USDA ARS, Southeast Poultry Research Laboratory, 934 College Station Rd, Athens, GA, 30605, USA. stivalis@uga.edu.
authors.forename: Stivalis
authors.initials: S
authors.lastname: Cardenas-Garcia
authors.affiliation: Department of Immunology and Microbiology, Wayne State University, Detroit, MI, 48201, USA. rsundick@med.wayne.edu.
authors.forename: Roy S
authors.initials: RS
authors.lastname: Sundick
authors.affiliation: USDA ARS, Southeast Poultry Research Laboratory, 934 College Station Rd, Athens, GA, 30605, USA. patti.miller@ars.usda.gov.
authors.forename: Patti J
authors.initials: PJ
authors.lastname: Miller
authors.affiliation: Department of Veterinary Pathology, College of Veterinary Medicine, University of Georgia, Athens, GA, 30605, USA. corbrown@uga.edu.
authors.forename: Corrie C
authors.initials: CC
authors.lastname: Brown
authors.affiliation: USDA ARS, Southeast Poultry Research Laboratory, 934 College Station Rd, Athens, GA, 30605, USA. Claudio.Afonso@ars.usda.gov.
authors.forename: Claudio L
authors.initials: CL
authors.lastname: Afonso
mesh_terms: D000818:Animals; D002461:Cell Line, Transformed; D002645:Chickens; D015870:Gene Expression; D007376:Interleukin-2 / Q000235:genetics*; D009521:Newcastle Disease / Q000235:genetics* / Q000473:pathology / Q000821:virology*; D009522:Newcastle disease virus / Q000302:isolation & purification / Q000472:pathogenicity / Q000502:physiology*; D019562:Viral Load; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism; D014774:Virulence; D014779:Virus Replication
chemical_list: D007376:Interleukin-2; D014764:Viral Proteins