NO SIGNS OF ACTIVITY MARKERS IN PERIPHERAL-BLOOD DESPITE INCREASED BRONCHIAL REACTIVITY AFTER REPEATED LOW-DOSE ALLERGEN EXPOSURE

The allergen inhalation test can be used as an experimental model to s tudy pathophysiological events in allergic asthma. Repeated low-dose i nhalations of allergen induce increased bronchial hyperresponsiveness (BHR) and resemble natural allergen exposure. The objective of the pre sent study was to investigate whether eosinophil recruitment and activ ation in peripheral blood, differences in expression of lymphocyte sur face antigens and increased bronchial responsiveness to histamine occu r during and after repeated low-dose bronchial allergen challenge. Fou rteen atopic asthmatic patients were challenged in a randomized double -blind manner for 7 days with either allergen in very low doses or pla cebo. We measured the concentration of eosinophils, eosinophil cationi c protein (ECP) and the expression of the EG2-epitope on intracellular ECP in eosinophils and the expression of lymphocyte surface antigen m arkers in peripheral blood. The challenge period started and ended wit h a histamine provocation. The repeated low-dose allergen exposure res ulted in a significant increase in BHR. No changes were seen in the pl acebo group. Concerning the inflammatory parameters in peripheral bloo d, no significant changes were seen during or after the week of low-do se allergen inhalations. Our results show that very low, repeated dose s of allergen induce increased airway reactivity despite lack of evide nt clinical symptoms or signs of activation of inflammatory cells in p eripheral blood.