Eosinophil degranulation status in allergic rhinitis: observations before and during seasonal allergen exposure

Despite the fact that extensive degranulation is a likely prerequisite for a pathogenic role of eosinophils, little is known about the degranulation status of these cells in eosinophilic conditions. The present study of the ultrastructure of tissue eosinophils explores eosinophil degranulation in allergic rhinitis before and during seasonal allergen exposure. A total of 23 patients scored symptoms q.d., prior to and during the pollen season. The numbers of mucosal eosinophils and their degranulation status were determined in nasal biopsies. Furthermore, nasal lavage fluid levels of eosinophil cationic protein (ECP) and alpha2-macroglobulin were assessed as indices of eosinophil activity and plasma exudation, respectively. Seasonal allergen exposure was associated with increased nasal symptoms, increased lavage fluid levels of ECP and alpha2-macroglobulin, and increased numbers of tissue eosinophils. In the tissue, transmission electron microscopy revealed a moderate piecemeal degranulation already prior to the season (mean+/-sd 37+/-2.7% altered granules). Seasonal allergen exposure increased this degranulation (87+/-1.8%), and produced local areas with extensive deposition of granule proteins. The degree of eosinophil degranulation correlated with levels of ECP in lavage fluids obtained at histamine challenge. In conclusion, this study demonstrated that the nasal mucosa in allergic rhinitis features moderately degranulated eosinophils already at nonsymptomatic baseline conditions. In association with the development of symptomatic seasonal allergic rhinitis, the tissue deposition of eosinophil granule proteins is dramatically elevated through increased eosinophil numbers, together with markedly augmented degranulation of individual cells.