Degranulation of nasal epithelial mast cells after challenge of allergen. An electron microscopic study with serial sections.

Degranulation of mast cells in the nasal epithelial space was investigated by observation of the morphological changes in serial ultrathin sections. Materials were scraped from the inferior turbinate in six patients with perennial nasal allergy immediately after the first sneezing attack during nasal challenge by allergen discs. Labyrinthic cavities occurred in one part of the cytoplasm, and contained amorphous or fibrillar remnants of granule matrices in more than half of the mast cells. These findings almost coincided with the initial changes observed in isolated rat mast cells induced by several histamine releasing agents. Some mast cells without labyrinth structures did not show any change in the majority of granules. Materials were also scraped from five patients ten minutes in the majority of granules. Materials were also scraped from five patients ten minutes after nasal provocation. A relatively large number of mast cells without labyrinth structures were observed. The main change was a reduction of electron density in the granule matrix, resulting in a fibrillar and reticular appearance. A pore situated between a reduced density granule and the cell membrane was occasionally observed. The neighbouring granules were connected by a tunnel. Small intracellular spaces containing small quantities of remnants of the granule matrices originated from the labyrinth structure. The concentration of dissolved antigen was reduced by sneezing and secretion. The findings were observed immediately after provocation changed, in a time lapse of ten minutes, while a small amount of antigen continued to react with the mast cells. Thus the findings observed ten minutes after provocation represent slowly occurring changes in mast cells. It can be further speculated that the mast cells in nasal allergy show both rapid and slow ultrastructural changes in accordance with the amount of inhaled antigen in the nasal cavity.