The late, but not early, asthmatic response is dependent on IL-5 and correlates with eosinophil infiltration

Early-phase reactions (EPRs) and late-phase reactions (LPRs) are characteri stic features of bronchial asthma, although the pathogenetic mechanisms res ponsible for each of the responses are not fully defined. A murine model of EPRs and LPRs was developed to investigate the role of IL-5 and eosinophil s in development of both responses. After initial intraperitoneal sensitiza tion and airway challenge to ovalbumin (OVA), mice were provoked by additio nal exposure to OVA. An EPR, characterized by a transient increase in airwa y responsiveness, was observed 5-30 minutes after antigen provocation. This response was followed by an LPR that reached its maximum at 6 hours after challenge and was characterized by increased airway responsiveness and sign ificant lung eosinophilia. The EPR was blocked by cromoglycate and albutero l, whereas the LPR was abolished by cromoglycate and hydrocortisone. Before provocation with allergen, administration of anti-IL-5 antibody prevented the influx of eosinophils into the lung tissue and abolished the LPR but no t EPR. These results suggest that IL-5 and eosinophils are essential for de velopment of the LPR, but not EPR, in this model.