In a mouse model of bleomycin-induced lung fibrosis, M-CSF null mice had a marked reduction in the number of AM and in pulmonary fibrosis features when compared with M-CSF wild type mice, supporting once again the importance of M-CSF in the pathogenesis of fibrotic lung diseases and the relevance of M-CSF MDMs to explore these disorders. The gene discussed is CSF1; the disease is lung disorder.