Are blood eosinophil number and activity important for the development of the late asthmatic reaction after allergen challenge?

A role for eosinophils in chronic asthma has recently gained substantial support. We hypothesized that in addition to eosinophil chemoattractants released in the lung, the availability of a sufficient number of blood eosinophils to be recruited and their increased activity are prerequisites for the development of asthma. To test this hypothesis the blood eosinophil number and serum levels of ECP (eosinophil cationic protein were measured before allergen challenge of 13 allergic asthmatics. Each individual was pretreated with either placebo or four inhalant anti-asthmatic drugs at random and blind in order to modulate the late asthmatic reaction (LAR). Irrespective of premedication the blood eosinophil number and serum-ECP levels were significantly higher before challenge when the challenge resulted in LAR. Only corticosteroids abrogated the development of LAR and also significantly reduced eosinophil activity as measured by serum-ECP. Thus the inherent activity of a sufficient number of eosinophils may be important determinants for the expression of allergic asthma.