Effects of MMP deficiency on IL-13–induced alterations in lung volume and alveolar size. CC10-rtTA-IL-13 transgene^– and transgene⁺ mice with wild-type and null MMP-9 or MMP-12 loci were generated and placed on dox water at 1 month of age. They were maintained on this regimen for an additional month, at which time their lungs were removed and fixed to pressure. Lung volume (a and c) and alveolar size (chord length; b and d) were assessed as described in Methods. The noted values represent the mean ± SEM of a minimum of five animals in each group (*P < 0.01).