Whereas the proportion of T- and B- cells was similar in IPF lungs compared to healthy lungs, both CD71– alveolar- and SPP1/osteopontin+ interstitial macrophages were found to be associated with disease severity (40, 41), suggesting that lung-resident macrophages contribute to fibrosis in IPF. This evidence concerns the gene TFRC and idiopathic pulmonary fibrosis.