Evaluation of airway hyperresponsiveness and bronchoalveolar lavage fluid in a fisher (F344) rat model of Alternaria sensitization

Allergens with intrinsic protease activity have been shown to enable Th2 priming, and allow the establishment of airway inflammation and airway hyperresponsiveness in Th1-skewed mice. We attempted to induce Th2 responses in the lung of Fisher (F344) rats, a Th1-skewed animal model, using a protease-containing crude Alternaria extract. Four groups of F344 rats were evaluated over a six-week period. Group 1 was sensitized to crude Alternaria in AlOH 3 and nebulized with crude Alternaria biweekly. Group 2 was sensitized to crude Alternaria in AlOH 3 and exposed to crude Alternaria biweekly via direct intranasal inoculation. Group 3 was not sensitized and nebulized with crude Alternaria biweekly. Group 4 was not sensitized and nebulized with saline biweekly. At the end of six weeks, airway hyperresponsiveness was determined by methacholine challenge. Right-sided bronchoalveolar lavage was performed, and cell counts with differentials were obtained from the bronchoalveolar fluid (BALF). Protease levels in the crude Alternaria extract were confirmed using a protease assay kit. No differences in airway hyperresponsiveness or BALF cell counts with differentials were observed between the four groups (p>0.05). A correlation between the absolute eosinophil count in the BALF and PC20 was observed (r s=-0.57). The protease level in the crude Alternaria extract was 130ng/mg protein. We were unable to induce airway hyperresponsiveness or evidence of Th2 responses in the BALF of F344 rats, despite the concentration of protease activity present in the crude Alternaria extract. Threshold doses of protease activity required to induce Th2 airway responses in rat models are currently unknown.