AHR and allergic asthma: Exacerbated AHR in C5-deficient animals was first suggested in gene-linkage studies by Karp et al [7] that showed C5 gene expression inversely correlates with the magnitude of allergen-induced AHR in an ovalbumin model of allergic asthma; C5 gene expression was found to be lower in mouse strains more susceptible to the development of allergen-induced AHR.