AIM: Recent studies in both rodents and humans indicated that bone marrow (BM)-derived stem cells were able to home to the liver after they were damaged and demonstrated plasticity in becoming hepatocytes. However, the question remains as to how these stem cells are activated and led to the liver and where the signals initiating the mechanisms of activation and differentiation of stem cells originate. The aim of this study was to investigate the influence of serum from liver-damaged rats on differentiation tendency of bone marrow-derived stem cells.METHODS: Serum samples were collected from rats treated with a 2-acetylaminofluorene (2-AAF)/carbon tetrachloride (CCl4) program for varying time points and then used as stimulators of cultured BM stem cells. Expression of M2- and L-type isozymes of rat pyruvate kinase, albumin as well as integrin-β1 were then examined by reverse transcription polymerase chain reaction (RT-PCR) to estimate the differentiation state of BM stem cells.RESULTS: Expression of M2-type isozyme of pyruvate kinase (M2-PK), a marker of immature hepatocytes, was detected in each group stimulated with experimental serum, but not in controls including mature hepatocytes, BM stem cells without serum stimulation, and BM stem cells stimulated with normal control serum. As a marker expressed in the development of liver, the expression signal of integrin-β1 was also detectable in each group stimulated with experimental serum. However, expression of L-type isozyme of pyruvate kinase (L-PK) and albumin, marker molecules of mature hepatocytes, was not detected in groups stimulated with experimental serum.CONCLUSION: Under the influence of serum from rats with liver failure, BM stem cells begin to differentiate along a direction to hepatocyte lineage and to possess some features of immature hepatocytes.