Priming of circulating human eosinophils following late response to allergen challenge

The eosinophil is recognized as an important effector cell in asthma. To investigate the role of eosinophils in the aetiology of asthma, we have examined whether peripheral blood eosinophils are primed following whole-lung allergen challenge. Nineteen mild asthmatics, who each demonstrated a late asthmatic response (LAR), were studied. The priming of eosinophils following allergen challenge was assessed by measuring: 1) platelet-activating factor (PAF) and complement factor 5a (C5a) stimulated H2O2 release upon fibrinogen-coated tissue culture plates (n = 8); and 2) ex-vivo cell survival (n = 11). Subjects were venepunctured before and 24 h after allergen challenge and eosinophils were prepared by immunomagnetic separation. Basal H2O2 release was increased from eosinophils following allergen challenge. The response to PAF stimulation was significantly increased in terms of cell sensitivity (negative log of concentration producing half the maximal effect (pD2)) and responsiveness (maximum effect Emax). With C5a, although there was no change in sensitivity there was a significant increase in the maximal response. Ex-vivo eosinophil survival (at 3 days and cell half-life) was significantly prolonged following allergen challenge. In conclusion, we have demonstrated the priming of circulating eosinophils following allergen challenge.