The degree of natural allergen exposure modifies eosinophil activity markers in the circulation of patients with mild asthma.

We have previously found that CD9, CD11b, and intracellular ECP (EG2) may be used as activity markers for eosinophils in vitro. The main object of the present study was to determine whether these markers can reflect eosinophil activation in vivo in relation to allergen exposure. for this purpose, six patients with a history of allergic rhinitis and occasional asthma symptoms during the pollen season participated. Blood donors served as controls. Peripheral blood eosinophils were analyzed according to the FOG method and flow cytometry, before and during one birch pollen season with high pollen load (HPL) and one with low pollen load (LPL). The CD9 expression on peripheral eosinophils from the patients was significantly increased both before (P < 0.05) and during (P < 0.01) HPL season, and CD11b expression solely during HPL season (P = 0.01) as compared to controls. The intracellular expression of the EG2 epitope was increased before (P < 0.01) and during (P < 0.05) HPL season, and increased significantly (P < 0.05) during season as compared to before. No changes were observed before and during LPL season. The proportion of eosinophils was increased both before (P < 0.05) and during (P < 0.001) the HPL season as compared to controls. The markers CD9, EG2, and, to a lesser extent, CD11b seem to detect activated eosinophils in the circulation, whereas EG2 may also reflect increased antigen exposure during season.