title: Blood MxA protein as a marker for respiratory virus infections in young children.
abstract: BACKGROUND
  Type I interferon induced MxA response can differentiate viral from bacterial infections, but MxA responses in rhinovirus or asymptomatic virus infections are not known.
  
  
  OBJECTIVE
  To study MxA protein levels in healthy state and during respiratory virus infection of young children in an observational prospective cohort.
  
  
  METHODS
  Blood samples and nasal swabs were collected from 153 and 77 children with and without symptoms of respiratory infections, respectively. Blood MxA protein levels were measured by an enzyme immunoassay and PCR methods were used for the detection of respiratory viruses in nasal swabs.
  
  
  RESULTS
  Respiratory viruses were detected in 81% of symptomatic children. They had higher blood MxA protein levels (median [interquartile range]) than asymptomatic virus-negative children (695 [345-1370] μg/L vs. 110 [55-170] μg/L; p < 0.001). Within asymptomatic children, no significant difference was observed in MxA responses between virus-positive and virus-negative groups. A cut-off level of 175 μg/L had 92% sensitivity and 77% specificity for a symptomatic respiratory virus infection. Rhinovirus, respiratory syncytial virus, parainfluenza virus, influenza virus, coronavirus, and human metapneumovirus infections were associated with elevated MxA responses. Asymptomatic virus-negative children vaccinated with a live virus vaccine had elevated MxA protein levels (240 [120-540] μg/L), but significantly lower than children with an acute respiratory infection, who had not received vaccinations (740 [350-1425] μg/L; p<0.001).
  
  
  CONCLUSIONS
  Blood MxA protein levels are increased in young children with symptomatic respiratory virus infections, including rhinovirus infections. MxA is an informative general marker for the most common acute virus infections.
authors.affiliation: Department of Paediatrics, Turku University Hospital, Turku, Finland; Turku Institute for Child and Youth Research, University of Turku, Turku, Finland.
authors.forename: Laura
authors.initials: L
authors.lastname: Toivonen
authors.affiliation: Department of Paediatrics, Turku University Hospital, Turku, Finland; Turku Institute for Child and Youth Research, University of Turku, Turku, Finland.
authors.forename: Linnea
authors.initials: L
authors.lastname: Schuez-Havupalo
authors.affiliation: Department of Paediatrics, Turku University Hospital, Turku, Finland; Turku Institute for Child and Youth Research, University of Turku, Turku, Finland.
authors.forename: Maris
authors.initials: M
authors.lastname: Rulli
authors.affiliation: Department of Clinical Microbiology, University of Eastern Finland, Kuopio, Finland; Immunogenetics Laboratory, University of Turku, Turku, Finland.
authors.forename: Jorma
authors.initials: J
authors.lastname: Ilonen
authors.affiliation: Department of Clinical Microbiology, University of Eastern Finland, Kuopio, Finland.
authors.forename: Jukka
authors.initials: J
authors.lastname: Pelkonen
authors.affiliation: Virology Unit, National Institute of Health and Welfare, Helsinki, Finland.
authors.forename: Krister
authors.initials: K
authors.lastname: Melen
authors.affiliation: Virology Unit, National Institute of Health and Welfare, Helsinki, Finland; Department of Virology, University of Turku, Turku, Finland.
authors.forename: Ilkka
authors.initials: I
authors.lastname: Julkunen
authors.affiliation: Department of Paediatrics, Turku University Hospital, Turku, Finland; Turku Institute for Child and Youth Research, University of Turku, Turku, Finland.
authors.forename: Ville
authors.initials: V
authors.lastname: Peltola
authors.affiliation: Department of Virology, University of Turku, Turku, Finland. Electronic address: matti.waris@utu.fi.
authors.forename: Matti
authors.initials: M
authors.lastname: Waris
mesh_terms: D015415:Biomarkers / Q000097:blood; D002097:C-Reactive Protein; D005260:Female; D006801:Humans; D007223:Infant; D007958:Leukocyte Count; D008297:Male; D064547:Myxovirus Resistance Proteins / Q000097:blood*; D011446:Prospective Studies; D012141:Respiratory Tract Infections / Q000097:blood* / Q000175:diagnosis / Q000821:virology*
chemical_list: D015415:Biomarkers; C579071:MX1 protein, human; D064547:Myxovirus Resistance Proteins; D002097:C-Reactive Protein
keywords: Interferon; MxA protein; Respiratory virus infection; Rhinovirus; Rotavirus vaccine; STEPS study