We have previously shown that infusion of bone marrow cells (BMC) improves CCl4-induced cirrhosis. However, it is unclear why the injected BMC are resistant to CCl4 damage and subsequently improve the local microenvironment in damaged liver. To analyze the cellular phenomena involved in this process, we studied the damaged liver using electron microscopy. We found that CCl4 caused rough endoplasmic reticula to swell in hepatocytes. To analyze the gene expression patterns associated with this process, we conducted PCR-selected suppressive subtractive hybridization. We found that expression levels of HSP84, HSP40, and XBP1 differed markedly between control liver and liver infused with BMC. Immunohistochemical staining revealed that expression levels of HSP84 and HSP40 were markedly higher in the early phase of differentiation immediately after BMC infusion, but decreased over time. XBP1 expression remained high during the late phase, and GRP78 expression increased with XBP1 activation. We also found that GFP-positive BMC expressed XBP1 and GRP78. XBP1 and GRP78 are associated with ER stress. Thus, continuous high XBP1 and GRP78 expression might be essential for the survival and proliferation of BMC in a CCl4-induced persistent liver damage environment. (C) 2007 Elsevier Inc. All rights reserved.