Following bleomycin-induced lung injury, Il11−/− mice are protected from pulmonary fibrosis and exhibit lesser ERK, STAT3 and NF-kB activation, reduced Il1b, Timp1, Ccl2 and diminished IL6 expression, both at baseline and after injury: placing Il11 activity upstream of IL6 in this model. Here, TIMP1 is linked to pulmonary fibrosis.