Nasal mast cell response to natural allergen exposure.

A redistribution of mast cells into the epithelium and towards the mucosal surface was previously observed during the allergy season in individuals allergic to birch pollen. We have therefore attempted to investigate in greater detail the role of mast cells in mucosal allergy by the study of the morphological and biochemical changes that occur in the nasal mucosa of allergic individuals during natural allergen exposure. An activation of the intraepithelial mast cells was indicated by the observation of ultrastructural signs of a secretory activity. We also found that the normal strong correlation between mast cell numbers and histamine content in the nasal mucosa was absent in specimens taken during allergen exposure, which was interpreted as a result of a release of histamine from the mast cells with the appearance of a transient, non-mast cell pool of tissue histamine. Furthermore, the histamine content of the nasal mucosa during the pollen season was strongly correlated to the severity of symptoms experienced by the patients. These observations provide additional evidence that mucosal mast cells have a pathogenetic role in continuous allergic airway disease.