Cytotoxicity Of IL-18 And Poly I:C-activated NK Cells On Hepatic Stellate Cells And Its Mechanism

Backgrounds:Sustained liver injury induced by multiple causes leads to the graduate replacement of normal structure of hepatic lobules by scar tissue,resulting in hepatic fibrosis and cirrhosis.Liver fibrosis remains a worldwide health problem due to the lack of effective treatments.Hepatic stellate cells are the key to liver fibrogenesis.It has been reported that NK cells inhibit hepatic stellate cells and progression of hepatic fibrosis.It has been reported that poly I:C,a ligand for Toll-like receptor 3,induces IL-18 secretion from Kupffer cells,which in turn activates NK cells.We hypothesized that poly I:C and IL-18 synergistically activate NK cells to inhibit hepatic stellate cells.To test the hypothesis,I have conducted studies on the activation of NK cells and their related mechanisms for inhibition of hepatic stellate cells.Methods:To study the activation of NK cells,we first isolated and purified NK cells from peripheral blood of healthy donors,then stimulated purified NK cells with IL-18 and poly I:C in vitro.NK cell phenotypes were detected by flow cytometry,secretion of IFN-γ was detected by intracellular staining and ELISA.In order to study the signal transduction of NK cell activation,after stimulated by IL-18/poly I:C,we used western blot to detect phosphorylation of signaling molecules in NK cells,and the regulatory effects of activated NK cells on hepatic stellate cells through cell co-culture.Apoptosis of hepatic stellate cells was identified by staining with PI and AnnexinV.Results:IL-18 and poly I:C synergistically activate the expression of CD69 and TRAIL on NK cells,and the secretion of IFN-γ by NK cells.IL-18 and poly I:C activate NK cells through the p38 MAPK/PI3 K signaling pathway.Activated NK cells kill hepatic stellate cells by degranulation-dependent mechanism.Interestingly,TRAIL expressed on the activated NK cells plays a critical role in the NK cell degranulation and death of hepatic stellate cells.Conclusions:NK cells are synergistically activated by IL-18 and poly I:C via p38 MAPK/PI3 K signaling pathways and kill hepatic stellate cells in a novel TRAIL-dependent degranulation mechanism.