AIM:To analyze and to compare the effects of interferon(IFN)-α,IFN-β,and IFN-γ on pancreatic stellate cell(PSC)activation in vitro and to elucidate the molecular basis ofIFN action.METHODS:PSCs were isolated from rat’s pancreatictissue,cultured and stimulated with recombinant ratIFNs.Cell proliferation and collagen synthesis wereassessed by measuring the incorporation of 5-bromo-2’-deoxyuridine(BrdU)into DNA and[~3H]-proline intoacetic acid-soluble proteins,respectively.Apoptoticcells were determined by FACS analysis(sub-G_1peak method).Exhibition of the myofibroblastic PSCphenotype was monitored by immunoblot analysis ofs-smooth muscle actin(α-SMA)expression.To assessthe activation of signal transducer and activator oftranscription(STAT),Western blots using phospho-STAT-specific antibodies were performed.In studies onSTAT1 function,expression of the protein was inhibitedby siRNA.RESULTS:IFN-β and IFN-γ,but not IFN-α signifcantlydiminished PSC proliferation and collagen synthesis.IFN-γ was the only IFN that clearly inhibited α-SMAexpression.Under the experimental conditions used,no enhanced rate of apoptotic cell death was observedin response to any IFN treatment.IFN-β and IFN-γinduced a strong increase of STAT1 and STAT3 tyrosinephosphorylation,while the effect of IFN-α was muchweaker.Inhibition of STAT1 expression with siRNA wasassociated with a significantly reduced growth-inhibitoryeffect of IFN-γ.CONCLUSION:IFN-β and particularly IFN-γ displayinhibitory effects on PSC activation in vitro and should be tested regarding their in vitro efficiency.Growthinhibition by IFN-γ action requires STAT1. AIM: To analyze and to compare the effects of interferon (IFN) -α, IFN-β, and IFN-γ on pancreatic stellate cell (PSC) activation in vitro and to elucidate the molecular basis of IFN action. METHODS: PSCs were isolated from rat’s pancreatictissue, cultured and stimulated with recombinant rat IFNs.Cell proliferation and collagen synthesis were assessed by measuring the incorporation of 5-bromo-2’-deoxyuridine (BrdU) into DNA and [~ 3H] -proline intoacetic acid-soluble proteins, respectively. were determined by FACS analysis (sub-G_1 peak method). Inhibition of the myofibroblastic PSCphenotype was monitored by immunoblot analysis ofs-smooth muscle actin (α-SMA) expression. As assthe activation of signal transducer and activator of transcription (STAT) phospho-STAT-specific antibodies were performed in studies on STAT1 function, expression of the protein was inhibited by siRNA.RESULTS: IFN-β and IFN-γ, but not IFN-α signifcantly diminished PSC proliferation and collagen synthesis IFN-γ was the only IFN that clearly inhibited α-SMA expression. Under der the experimental conditions used, no enhanced rate of apoptotic cell death was observed in response to any IFN treatment. IFN- β and IFN-γinduced a strong increase of STAT1 and STAT3 tyrosinephosphorylation, while the effect of IFN-α was much weaker. Inhibition of STAT1 expression with siRNA wasassociated with significantly reduced growth inhibitory effect of IFN-γ. CONCLUSION: IFN-β and particularly IFN-γ display inhibitory effects on PSC activation in vitro and should be tested regarding their in vitro efficiency. Growth Inhibition by IFN-γ action requires STAT1.