Methods: Non asthmatic subjects with seasonal allergic rhinitis were recruited. At baseline (out of the pollen season), skin prick tests, spirometry, methacholine bronchoprovocation, blood sampling and sputum induction were performed. At the peak of rhinitis symptoms, the same tests were repeated. Fibrocytes number and level of activation were determined in whole blood. Cells were stained for fibrocyte markers (CD34, CD45, CXCR4, collagen I) and analyzed by flow cytometry.
Results: Eighteen subjects (12F:6M) aged 31 ± 9 years were recruited. During the pollen season, the percentage of blood fibrocytes significantly decreased (median [25-75 percentile], 10.1 [6.4-20.7]% vs 3.7 [4.2-10.1]%, P=0.03) in subjects sensitized to trees and significantly increased (15.5 [9.9-23.1]% vs 64.0 [57.6-73.6]%, P=0.001) in subjects allergic to grass. No significant difference in mean fluorescence of CXCR4 was observed between baseline and pollen season (mean ± SD: 1759 ± 682 vs 1454 ± 795 (arbitrary units), P=0.19).
Conclusions: The number of blood fibrocytes varies during pollen season according to allergen exposure but may indicate an active migration of these cells from the periphery to the airways. A prolonged pollen exposure could lead to the increase of blood fibrocytes. These results may help identify predictors of asthma development.