title: Elevated peripheral allergen-specific T cell response is crucial for a positive atopy patch test reaction.
abstract: BACKGROUND
  Atopic eczema is a chronic inflammatory skin disease in which several subgroups of cases can be identified. Atopy patch testing (APT) reveals allergen sensitization also in atopic eczema patients devoid of detectable allergen-specific IgE, suggesting the importance of factors other than IgE in the reaction. Here we investigate the relationship between APT reactions and allergen-specific peripheral IgE and T cell reactivity in atopic eczema patients.
  
  
  METHODS
  Adult patients with atopic eczema (n = 64) and healthy controls (n = 24) were analyzed for reactivity to Malassezia sympodialis extract by APT, measurement of specific plasma IgE and in vitro determination of the frequency of allergen-reactive peripheral blood mononuclear cells producing interleukin-4 and interleukin-5 using the ELISpot method.
  
  
  RESULTS
  When combining the results of the APT, IgE measurements and the ELISpot analyses, reactivity to M. sympodialis was found in a majority of the atopic eczema patients (69%), whereas the healthy controls were negative throughout. T cell reactivity to M. sympodialis, manifested by production of both interleukins 4 and 5, was highly predictive for a positive APT reaction and displayed a strongly positive correlation with the APT score. In contrast, the allergen-specific IgE levels did not predict the APT outcome, and no correlation could be found between the IgE levels and the APT score.
  
  
  CONCLUSIONS
  Peripheral allergen-specific T helper 2 cell-mediated reactivity appears to be required for a positive APT reaction to M. sympodialis. The diagnostic potential of measuring peripheral allergen-specific T cell responses should be considered in atopic eczema.
authors.affiliation: Clinical Allergy Research Unit, Department of Medicine Solna, Karolinska Institutet and University Hospital, Stockholm SE-171, Sweden. Catharina.Johansson@ki.se
authors.forename: Catharina
authors.initials: C
authors.lastname: Johansson
authors.forename: Niklas
authors.initials: N
authors.lastname: Ahlborg
authors.forename: Anna
authors.initials: A
authors.lastname: Andersson
authors.forename: Lena
authors.initials: L
authors.lastname: Lundeberg
authors.forename: Maria A
authors.initials: MA
authors.lastname: Karlsson
authors.forename: Annika
authors.initials: A
authors.lastname: Scheynius
authors.forename: Maria
authors.initials: M
authors.lastname: Tengvall Linder