PGE2 exerts a protective effect on fibroblasts as previously mentioned, and GM-CSF deficiency leads to an enhanced level of fibrosis in bleomycin-induced pulmonary fibrosis, with a mechanism of action involved in this effect identified as the impaired production of potent anti-fibrotic PGE2 in macrophages (Moore et al., 2000). Here, CSF2 is linked to pulmonary fibrosis.