Direct in vivo evidence for mast cell degranulation during allergen-induced reactions in man

There is little or no direct in vivo evidence in man to support the involvement of mast cell-mediator release in the pathogenesis of immediate allergic reactions. We have performed a within-subject controlled study to determine the changes that occur in nasal mast cells during allergen-induced rhinitis. Twelve subjects with asymptomatic rhinitis were studied. Nasal biopsy specimens were obtained from each subject after a control solution (isotonic saline, 0.9% w/v) had been nebulized into one nostril and allergen solution (freeze-dried allergen extract reconstituted with isotonic saline) into the other. The tissues obtained were fixed in Carnoy's solution and stained with the alpha-naphthol AS-D chloroacetate esterase reaction (N AS-D CA ER). Mast cells were counted under light microscopy in the epithelium and lamina propria, and the integrity of each cell was assessed. No significant differences were found in the number of epithelial or lamina propria mast cells in biopsy specimens obtained after saline or allergen administration. However, the number of degranulated mast cells after allergen provocation (89%) was significantly greater than after instillation of control solution (15%) (p = 0.003). Changes of mast cell degranulation after allergen provocation were confirmed by electron microscopy. In six nonatopic, control subjects without rhinitis, there was no significant difference between the percentages of degranulated mast cells after allergen provocation (25.8%) and instillation of saline (24.3%). This study provides direct in vivo evidence for allergen-induced mast cell activation in man.