Background IL-5 is a specific cytokine for eosinophil accumulation, activation and prolongation of survival and can be recovered in elevated concentrations from the bronchoalveolar compartment in atopic asthma following allergen challenge.
Objective The action of IL-5 is mediated via the specific IL-5 receptor-α (IL-5Rα). Although in vitro data suggest that IL-5R expression is regulated by cytokines such as IL-3, IL-5 and GM-CSF, IL-5R regulation in vivo and its kinetics following allergen provocation are incompletely understood.
Methods We investigated IL-5R regulation in vivo following segmental allergen provocation (SAP) with an individually standardized dose of allergen in 12 patients with atopic asthma. Lavage was performed 10 min and 18 h (eight patients) and 10 min and 42 h (eight patients) after allergen challenge. In addition to differential cell counts, IL-5Rα was measured by flow cytometry and IL-5 concentrations in bronchoalveolar lavage (BAL) fluid were determined by ELISA.
Results IL-5Rα expression decreased significantly on peripheral blood and on BAL eosinophils 18 and 42 h after SAP. In contrast, IL-5 concentrations increased significantly in BAL fluid 18 and 42 h after SAP. In four and two patients, respectively, there were detectable IL-5 concentrations in serum 18 or 42 h after allergen exposure.
Conclusions Although there was no correlation between IL-5 concentrations and IL-5Rα expression on eosinophils in BAL, our data support previous in vitro and in vivo findings of a negative feedback mechanism between IL-5 concentrations and IL-5Rα expression on eosinophils.