Diminished response to grass pollen allergen challenge in subjects with concurrent house dust mite allergy.

INTRODUCTION: The clinical manifestation of allergic rhinitis is influenced by many factors; while different subpopulations are not well defined. Different combinations of allergic sensitization may lead to different clinical manifestations of allergic disease. METHODS: In a nasal allergen challenge model we compared allergic rhinitis symptoms between subjects mono-sensitized to grass pollen or house dust mite, poly-sensitized subjects, and healthy controls. We measured visual analogue scales of symptoms and peak nasal inspiratory flow. We also compared serum total IgE, allergen-specific IgE and IgG4, and basophil histamine release. RESULTS: Nasal challenge with grass pollen extract led to a significantly larger increase in subjective (p = 0.031) and objective (p = 0.001) nasal symptoms in grass pollen mono-sensitized subjects than in poly-sensitized subjects. No differences were found in serum levels of allergen-specific IgE and IgG4 or in biological activity of IgE (basophil histamine release) between mono-sensitized and poly-sensitized subjects. We found a strong inverse correlation between serum allergen-specific IgE and basophil histamine release (-0.789, p = 0.001). CONCLUSIONS: Grass pollen mono-sensitized subjects have a more severe clinical response to nasal challenge than poly-sensitized subjects. This cannot be explained by serum levels of IgE or its biological activity. The continuous allergen exposure in poly-sensitized subjects may alter local immuno-regulatory processes, leading to a reduced clinical response to allergen challenge.