Repeated inhalation of low doses of cat allergen that do not induce clinical symptoms increases bronchial hyperresponsiveness and eosinophil cationicprotein levels

The aim of this study was to investigate whether repeated exposure to subcl inical doses of cat allergens, not inducing asthma symptoms, could affect e osinophil cationic protein (ECP) levels in bronchoalveolar lavage (BAL) or in peripheral blood, without the appearance of clinical symptoms. Twelve pa tients with mild asthma, all sensitized to cats and not exposed to cat alle rgen at home, underwent a series of inhalations of cat allergen or placebo for 8 days over 2 weeks. A methacholine challenge was performed before and after the allergen and saline exposures, and BAL and blood were sampled for ECP measurements and eosinophil counts. No patients experienced asthma sym ptoms. However, PD20 methacholine (geometric mean) decreased significantly from 263 mu g before to 126 mu g after inhalation of allergen. Inhalation o f saline did not induce any significant change in PD20. The change in log P D20 before and after cat allergen exposure was statistically different from the change in log PD20 before and after saline. Median ECP levels in BAL a nd serum increased significantly after allergen exposure, from 0.8 to 3.1 m u g/l (p<0.02) and from 15.9 to 31.4 mu g/l (p<0.05), respectively. No chan ge was observed after saline inhalations. The change in BAL and serum ECP l evels was statistically significant compared to that in the control group. The number of eosinophils did not change, however, nor did IL-5 and RANTES levels in BAL and serum. In conclusion, our results show that (1) exposure of asthma patients to repeated low doses of allergen, which did not provoke any clinical symptoms, is capable of inducing a local eosinophil activatio n associated with an increase in nonspecific bronchial hyperresponsiveness and (2) the increase in serum ECP levels due to eosinophil activation prece des the occurrence of asthma symptoms and may thus be a marker of allergen exposure in allergic asthma.