As a result, Tm4sf5-knockout C57BL/6 mice have ameliorated bleomycin-induced lung fibrosis compared to the fibrosis in Tm4sf5-expressing wild type mice, in which the architecture of the lung epithelium is disrupted, leading to the accelerated death of type I AECs and hyperplasia of type II AECs. Here, TM4SF5 is linked to pulmonary fibrosis.