The role of macrophage-derived Wnt proteins in pulmonary fibrosis has been analyzed in a co-culture system in Hou's study, which showed that M2 macrophages (IL-4–stimulated RAW cells, CD68+ CCR7−CD206+), but not M1 macrophages (LPS-stimulated, CD68+ CCR7+CD206−), promote myofibroblast differentiation of lung-resident mesenchymal stem cells through the release of Wnt7a (149). Here, IL4 is linked to pulmonary fibrosis.