Optimisation of the sensitisation conditions for an ovalbumin challenge model of asthma.

Antigen inhalation in patients with atopic asthma results in an early asthmatic response (EAR), accompanied by a late asthmatic response (LAR) in 60% of patients, airway hyperresponsiveness (AHR) and inflammatory cell infiltration to the lungs. An ideal animal model of asthma should, therefore, provide at least these 4 features consistently and reproducibly. The aim of this study was to optimise the ovalbumin (OA) sensitisation conditions, for achieving EAR, LAR, AHR and cell influx, in a guinea-pig model of asthma. Animals were sensitised with 10 micro g or 100 micro g OA, as either a single or booster (day 1 and day 5) injection. Airway responses to inhaled OA (10 micro g, 1 h) of actively sensitised, conscious guinea pigs were determined by whole body plethysmography as the change in specific airways conductance (sG(aw)) over a 12 h period and at 24 h. Bronchoconstriction by inhaled histamine (1 mM) was used to investigate AHR, and inflammatory cell influx was determined by bronchoalveolar lavage (BAL), both at 24 h post-challenge. A single sensitisation with 10 micro g OA did not reveal an EAR, LAR or AHR following exposure to OA. However, total and differential cell counts (eosinophils and macrophages) were significantly greater 24 h post-challenge, when compared to saline-challenged sensitised animals. The addition of a booster injection of 10 micro g revealed an EAR, but no LAR or AHR after ovalbumin inhalation. However, there was a significant cell influx. Sensitisation with 100 micro g OA (single and booster injections) revealed all four parameters of the asthmatic response (EAR, LAR, AHR and cell influx). The incorporation of the booster sensitisation injection resulted in a prolongation of the LAR, and the AHR was more pronounced and cell influx increased significantly, when compared to all other sensitisation protocols. Thus, sensitisation with 100 micro g OA (with a booster injection) can reveal an EAR, LAR, AHR and cell influx following inhalation exposure to OA (10 micro g). Cellular infiltration to the lung may be a poor marker of the asthmatic response, as a threshold level of cell influx (eosinophils) appears to be required in order to elicit the LAR and AHR. There was an association between the LAR and AHR.