Effects of Allergen Challenge on Eosinophils, Eosinophil Cationic Protein, and Granulocyte-Macrophage Colony-Stimulating Fador in Mild Asthma K. L. WOOLLEY, E. ADELROTH, M. J. WOOLLEY, R. ELLIS, M. JORDANA, and P. M. O'BYRNE Departments of Medicine and Pathology, McMaster University, Hamilton, Ontario, Canada Allergen inhalation challenge is associated with increases in eosinophil number and activation, and pro- vides a useful model for investigating airway inflammation in asthma. Limited information, however, is avail- able on the effect of allergen challenge on cytokines regulating eosinophil function. We investigated allergen- induced changes in eosinophil number and activation and in granulocyte-macrophage colony-stimulating factor (GM-CSF), a cytokine known to regulate eosinophil function in vitro. Seven subjects with mild atopic asthma and late asthmatic responses completed diluent- and allergen-inhalation challenges. Blood, bron- choalveolar lavage fluid (BALF), and biopsy samples were collected 24 h after challenge. Allergen inhala- tion caused a significant increase in eosinophils in BALF and biopsy samples. Eosinophil activation, as assessed by secretion of eosinophil cationic protein, and GM-CSF levels were significantly increased in BALF and bronchoalveolar lavage (BAL) cells. Allergen inhalation did not cause a significant change in eosinophil activation in biopsy tissue but did result in a significant decrease in GM-CSF in the tissue. Sig- nificant correlations were shown between the concentration of GM-CSF in BALF and the percentage of BAL eosinophils (Rs = 0.75, P = 0.05), severity of the late asthmatic response, and number of BAL eo- sinophils (Rs = 0.82, P = 0.02). A trend was seen between the late response and the concentration of GM-CSF in BALE These results are consistent with the hypothesis that eosinophils, regulated by GM-CSF, contribute to allergen-induced decreases in airway function. Woolley KL, Adelroth E, Woolley MJ, Ellis R, Jordana M, O'Byrne PM. Effects of allergen challenge on eosinophils, eosinophil cationic protein, and granulocyte-macrophage colony-stimulating factor in mild asthma. Am J Respir Crit Care Med 1995;151 :1915-24. Asthma is a disease characterized by variable airflow obstruc- tion and airway hyperresponsiveness (1). Recently, increased at- tention has been directed toward the relationship between airway inflammation and the changes in airway function associated with asthma. This relationship has been investigated in the laboratory using allergen challenge. The late asthmatic response, which oc- curs in some sensitized asthmatic individuals from 3 to 8 h after allergen inhalation, is characterized by the development of air- way obstruction and increases in airway responsiveness (2, 3). These physiologic changes are thought to be a consequence of allergen-induced inflammatory events occurring within asthmatic airways (2). The eosinophil has been implicated as an important effector cell contributing to the late asthmatic response (4). Increases in the number of eosinophils and their progenitors in blood (5-7), (Received in original form June 20, 1994) Supported by the Medical Research Council of Canada and a grant from Astra Pharma, Inc. (Canada). Ms. Woolley is the recipient of a Canadian Commonwealth Scholarship. Dr. Jordana isthe recipient of a Medical Research Council Scholarship Award. Dr. O'Byrne is the recipient of a Medical Council of Canada Scientist Award. Correspondence and requests for reprints should be addressed to Dr. P. M. O'Byrne, Department of Medicine, Rm. 3V-1,Health Sciences Center, McMaster University, 1200 Main Street West, Hamilton, Ontario, Canada L8N 325. Am J Respir Crit Care Med Val 151. pp 1915-1924,1995 and increases in eosinophils in bronchoalveolar lavage fluid (BALF) (3, 8-10) and induced sputum (11), have been reported to occur in asthmatic individuals who have developed late asth- matic responses. Eosinophil activation also occurs, with increases documented in the levels of preformed and newly generated medi- ators in the serum (12, 13) and BALF (8) of persons with asthma who have developed late asthmatic responses. Not all studies, however, have confirmed these findings (14). Most recently, in- vestigators have examined bronchial biopsy tissue to obtain in- formation on inflammatory events occurring within the airway wall. Todate, however, results have been inconsistent, with an increase (15) or no change (14, 16) reported in eosinophil numbers. Limited information is also available about eosinophil activation in the bron- chial mucosa. Beasley and associates (14) reported no changes in eosinophil activation following allergen challenge, on the ba- sis of an absence of changes in the ultrastructural appearance of eosinophil granules. However,Bentley and colleagues (17) and Aalbers and coworkers (18) reported increases in eosinophil acti- vation based on increased immunostaining for eosinophil cationic protein (ECP) following allergen challenge. In subjects developing late asthmatic responses, the recruit- ment and activation of airway eosinophils may involve the release of granulocyte-macrophage colony-stimulating factor (GM-CSF), a cytokine that has been shown in vitro to be chemotactic for eo- sinophils (19) and can enhance eosinophil survival and activa- tion (20, 21). After local allergen challenge, an increase has been reported in the number of cells expressing messenger ribonucleic