Ovalbumin Challenge Following Immunization Elicits Recruitment of Eosinophils but not Bronchial Hyperresponsiveness in Guinea-pigs: Time Course and Relationship to Eosinophil Activation Status

Eosinophils are known to be present in the airways of allergic asthmatics, and have been suggested to contribute to the pathophysiological changes accompanying this condition, particularly hyperresponsiveness to airway spasmogens. However, a causal relationship between pulmonary eosinophil accumulation and bronchial hyperresponsiveness in asthma is not proven. In the present study, the time course of pulmonary cell influx was investigated in an immunized guinea-pig model. Eosinophil activation status was also determined together with the bronchial responsiveness to histamine. Guinea-pigs were sensitized [20 μg ovalbumin (OVA) per animal in Al(OH)₃(0.5 ml) ip] and subsequently challenged with aerosolized OVA (100 μg/ml) for 1 h 18–21 days later. At different time points (1 h to 72 h) after OVA challenge, bronchial responses to iv histamine were measured and bronchoalveolar lavage (BAL) was performed to assess pulmonary cell influx. Eosinophil peroxidase (EPO) and total protein levels were measured in BAL fluid supernatants. Exposure of sensitized animals to aerosolized OVA produced a significant increase (P<0.05 vs. sham immunized) in eosinophil infiltration 24 h later which was sustained up to 72 h. Despite this, OVA challenge did not cause either eosinophil activation, as measured by EPO release, or bronchial hyperresponsiveness to histamine at any of the time points examined. These data show that allergen challenge of sensitized guinea-pigs can elicit airway eosinophil accumulation without accompanying airways hyperresponsiveness or eosinophil activation.