Seminal studies in animal models of allergic asthma demonstrated that selective neutralization of IL-13 reduced airway hypersensitivity (AHR), bronchoalveolar lavage (BAL) eosinophils, and mucus overproduction (Grunig et al., 1998; Wills-Karp et al., 1998). Here, IL13 is linked to allergic asthma.