title: Effect of anti-IgE therapy on food allergen specific T cell responses in eosinophil associated gastrointestinal disorders.
abstract: BACKGROUND
  Anti-IgE therapy inhibits mast cell and basophil activation, blocks IgE binding to both FcεRI and CD23 and down regulates FcεRI expression by antigen (Ag) presenting cells (APCs). In addition to its classical role in immediate hypersensitivity, IgE has been shown in vitro to facilitate Ag presentation of allergens, whereby APC bound IgE preferentially takes up allergens for subsequent processing and presentation. The purpose of this study was to determine whether anti-IgE therapy, by blocking facilitated Ag presentation in vivo, attenuates allergen specific Th2 cell responses.
  
  
  METHODS
  To test this hypothesis, food allergen specific T cell responses were examined during a 16-week clinical trial of omalizumab in nine subjects with eosinophilic gastroenteritis and food sensitization. Allergen specific T cell responses were measured using carboxyfluorescein succinimidyl ester dye dilution coupled with intracellular cytokine staining and polychromatic flow cytometry. Four independent indices of allergen specific T cell response (proliferation, Ag dose response, precursor frequency, and the ratio of Th2:Th1 cytokine expression) were determined.
  
  
  RESULTS
  Eight of the 9 subjects had measurable food allergen specific responses, with a median proliferation index of 112-fold. Allergen specific T cell proliferation was limited to CD4 T cells, whereas CD8 T cell did not proliferate. Food allergen specific responses were Th2 skewed relative to tetanus specific responses in the same subjects. In contradistinction to the original hypothesis, anti-IgE treatment did not diminish any of the four measured indices of allergen specific T cell response.
  
  
  CONCLUSIONS
  In sum, using multiple indices of T cell function, this study failed to demonstrate that anti-IgE therapy broadly or potently inhibits allergen specific T cell responses. As such, these data do not support a major role for IgE facilitated Ag presentation augmenting allergen specific T cell responses in vivo.
  
  
  BACKGROUND
  ClinicalTrials.gov identifier NCT00084097.
authors.affiliation: Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA. cprussin@niaid.nih.gov.
authors.forename: Barbara
authors.initials: B
authors.lastname: Foster
authors.forename: Shabnam
authors.initials: S
authors.lastname: Foroughi
authors.forename: Yuzhi
authors.initials: Y
authors.lastname: Yin
authors.forename: Calman
authors.initials: C
authors.lastname: Prussin