This would explain seemingly contradictory findings that Cela1−/− and KF4-treated mice develop less emphysema in response to 6 months of cigarette smoke exposure compared to wild-type or IgG-treated mice, (8) but cigarette smoke-exposed AAT−/−&Cela1−/− mice have slightly but significantly greater emphysema than AAT−/− mice (7). This evidence concerns the gene SERPINA1 and pulmonary emphysema.