Most importantly, intratracheal administration of Mecp2 siRNA‐loaded liposomes significantly reversed established pulmonary fibrosis and reduced the number of infiltrating M2 macrophages, as shown by the lower number of F4/80+CD206+CD11c− cells in the lungs than in Scr siRNA‐loaded liposomes‐treated lungs. The gene discussed is MECP2; the disease is pulmonary fibrosis.