TLR4 and pulmonary fibrosis: Furthermore, as the overexpression of TLR4 in lung tissue was accompanied by the aggravation of fibrosis, it is reasonable, based on our previous in vitro study, to speculate that the LPS challenge could induce the overexpression of TLR4 in mice lung fibroblasts, thereby enhancing their sensitivity to LPS and activating lung fibroblasts to initiate the progress of pulmonary fibrosis.