ACTA1 and idiopathic pulmonary fibrosis: However, in CTD-UIP HLFs, addition of TGF-β1 significantly increased IP-10 secretion and down-regulated α-SMA expression (Fig. 7, P < 0.01), suggesting that UIP-HLFs have an opposite response to TGF-β1 stimulation compared with NHLFs, and that the negative regulatory effect of IP-10 on α-SMA expression may be downstream of the TGF-β1 pathway.