The fact that the male arg‐ii−/− mice reveal lower levels of macrophage markers F4/80, hydroxyproline content, p16ink4 as compared with wt control animals despite no age‐associated increase in Arg‐II, suggests that basal levels of Arg‐II indeed play a role in pulmonary fibrosis in males. This evidence concerns the gene CDKN2A and pulmonary fibrosis.