Model of allergic bronchoconstriction in the guinea pig. 2. Recurrent reactions in individual animals

Characterization of allergen-induced bronchial hyperresponsiveness and airway inflammation in actively sensitized brown-Norway rats

Bronchial responsiveness to inhaled acetylcholine (ACh) and inflammatory cell recruitment in bronchoalveolar lavage fluid (BALF) were studied in inbred Brown-Norway rats actively sensitized to, and later exposed to, ovalbumin (OA). We examined animals 21 days after initial sensitization at 18 to 24 hours, or 5 days after a single challenge, or after the last of seven repeated exposures administered every 3 days. BALF was examined as an index of inflammatory changes within the lung. Animals repeatedly exposed to OA aerosols had an increased baseline lung resistance and a significant increase in bronchial responsiveness to inhaled ACh compared to control animals at both 18 to 24 hours and 5 days after the last OA exposure. Sensitized animals receiving a single OA aerosol also demonstrated bronchial hyperresponsiveness (BHR) to inhaled ACh (p less than 0.01) at 18 to 24 hours of a similar order as the multiple-exposed group. There was a significant increase in eosinophils, lymphocytes, and neutrophils in BALF at 18 to 24 hours but not at 5 days after single or multiple exposure to OA aerosol in the sensitized groups. Control animals demonstrated no changes in bronchial responsiveness, although a small but significant increase in inflammatory cells was observed compared to saline-only treated animals. There was a significant correlation between bronchial responsiveness and eosinophil counts in the BALF in the single allergen-exposed group (Rs = 0.68; p less than 0.05). We conclude that (1) BHR after allergen exposure in sensitized rats is associated with the presence of pulmonary inflammation but persists despite the regression of inflammatory cells in BALF after multiple OA exposures, and (2) this rat model has many characteristics of human allergen-induced BHR.

Characteristics of weekly pulmonary hypersensitivity responses elicited in the guinea pig by inhalation of ovalbumin aerosols

We have reported the development of a guinea pig animal model for pulmonary hypersensitivity to inhaled chemicals in which respirations of animals are monitored continuously for 24 hr permitting detection of immediate- (IAR) and late-onset (LAR) airway reactions. Additionally implanted temperature transmitters allow determination of accompanying febrile responses. The current study investigated the relationship between severity of IAR and occurrence of LAR in individual animals. To quantify severity, a grading system was devised which took into account time to response, increase in breathing rate, and occurrence of airway constriction (ACR). Guinea pigs were sensitized by ip injection with 1 mg ovalbumin (OA). On Day 14, inhalation challenge with 12 mg/m3 OA resulted in severe IAR in all animals. No LAR were detected. Subsequent weekly inhalation challenges with OA resulted in less severe IARs and occasionally in absence of response. Febrile reactions were not detected. On one occasion a LAR was observed. It occurred in the animal demonstrating the most severe IARs and having the highest titer of specific homocytotropic antibody. These results are consistent with the mechanism of IAR involving release of spasmogenic mediators from mast cells as a result of antigen crosslinking of surface antibody. The mechanism of the LAR is addressed in the accompanying paper in which LARs are more consistently produced in OA-sensitized guinea pigs.