The eosinophilic granulocyte an active participant in the late phase asthmatic reaction?

The role of the eosinophilic granulocyte in immediate hypersensitivity reactions is generally believed to be a beneficial one since this cell may phagocytose mast cell granules and inactivate certain mast cell mediators. However it has become clear that the eosinophilic granulocyte also has potent secretory capacities, and by this property may contribute in a detrimental way to the allergic process. In studying the late phase allergen induced bronchoconstriction by means of bronchoalveolar lavage (BAL) an evident infiltration of eosinophilic granulocytes in the bronchioli in the beginning of the late phase asthmatic reaction was noticed. Since also eosinophil cationic protein (ECP) has been reported to be elevated in the lavage fluid an active secretory role of the eosinophil in the late phase asthmatic reaction seemed likely. Although the release of ECP and other granular proteins may contribute to epithelial damage and inflammation and thereby to an increase in bronchial hyperreactivity they do not explain the late phase bronchoconstrictive reaction. Since leukotrienes were thought possible candidates to cause this reaction it was decided to isolate eosinophils from human peripheral blood and to study their leukotriene synthesis pattern. To our surprise purified human eosinophils almost exclusively synthesize the strongly bronchoconstrictive leukotriene LTC4 in considerable quantities upon in vitro stimulation with either the calcium-ionophore A23187 or opsonized zymosan. These findings suggest that the eosinophil may play an active role in causing the late phase asthmatic reaction.