Opn KO mice displayed evidently reduced lung fibrosis compared with WT, indicated by attenuated fibrotic focus formation and ECM deposition during both the acute and chronic responses, demonstrating that OPN indeed plays an important role in both the early and late stages of MWCNT-induced fibrosis development (Figs. 3 and 4). Here, SPP1 is linked to pulmonary fibrosis.