AIM:Recent studies in both rodents and humans indicatedthat bone marrow(BM)-derived stern cells were able to hometo the liver after they were damaged and demonstratedplasticity in becoming hepatocytes.However,the questionremains as to how these stem cells are activated and led tothe liver and where the signals initiating the mechanisms ofactivation and differentiation of stem cells originate.Theaim of this study was to investigate the influence of serumfrom liver-damaged rats on differentiation tendency of bonemarrow-derived stem cells.METHODS:Serum samples were collected from rats treatedwith a 2-acetylaminofluorene(2-AAF)/carbon tetrachloride(CCl_4)program for varying time points and then used asstimulators of cultured BM stem cells.Expression of M_2-andL-type isozymes of rat pyruvate kinase,albumin as well asintegrin-βl were then examined by reverse transcriptionpolymerase chain reaction(RT-PCR)to estimate thedifferentiation state of BM stem cells.RESULTS:Expression of M_2-type isozyme of pyruvate kinase(M_2-PK),a marker of immature hepatocytes,was detectedin each group stimulated with experimental serum,but notin controls including mature hepatocytes,BM stem cellswithout serum stimulation,and BM stem cells stimulatedwith normal control serum.As a marker expressed in thedevelopment of liver,the expression signal of integrin-β1 wasalso detectable in each group stimulated with experimentalserum.However,expression of L-type isozyme of pyruvatekinase(L-PK)and albumin,marker molecules of maturehepatocytes,was not detected in groups stimulated withexperimental serum.CONCLUSION:Under the influence of serum from rats withliver failure,BM stem cells begin to differentiate along adirection to hepatocyte lineage and to possess some featuresof immature hepatocytes. AIM: Recent studies in both rodents and humans showed that bone marrow (BM) -derived stern cells were able to home to the liver after they were damaged and demonstrated plasticity in becoming hepatocytes. However, the questionremains as to how these stem cells are activated and led tothe liver and where the signals initiating the mechanisms of activation and differentiation of stem cells originate. aim of this study was to investigate the influence of serum from liver-damaged rats on differentiation tendency of bonemarrow-derived stem cells. METHODS: Serum samples were collected from rats treatedwith a 2-acetylaminofluorene (2-AAF) / carbon tetrachloride (CCl 4) program for varying time points and then used asstimulators of cultured BM stem cells. Expression of M_2-and L-type isozymes of rat pyruvate kinase, albumin as well as integrin-βl were then examined by reverse transcription polymerase chain reaction (RT-PCR) to estimate the differentiation state of BM stem cells .RESULTS: Expression of M_2-type iso zyme of pyruvate kinase (M_2-PK), a marker of immature hepatocytes, was detectedin each group stimulated with experimental serum, but notin controls including mature hepatocytes, BM stem cellswithout serum stimulation, and BM stem cells stimulatedwith normalcontrol serum. As a marker expressed in the development of liver, the expression signal of integrin-β1 wasalso detectable in each group stimulated with experimental serum. Host, expression of L-type isozyme of pyruvate kinase (L-PK) and albumin, marker molecules of mature hepatocytes, was not detected in groups stimulated withexperimental serum. CONCLUSION: Under the influence of serum from rats withliver failure, BM stem cells begin to differentiate along adirection to hepatocyte lineage and to possess some features of immature hepatocytes.