The Role of Biliary Epithelial Cells in the Immunopathogenesis of Non-Suppurative Destructive Cholangitis in Murine Hepatic Graft-Versus-Host Disease

摘要

Non-suppurative destructive cholangitis (NSDC) is characterized by T-cell infiltration of the biliary epithelia of small-to medium-caliber bile ducts, causing apoptosis of biliary epithelial cells (BEC) and, ultimately, ductopenia. NSDC is the primary histopathologic process in the autoimmune disease known as primary biliary cirrhosis (PBC) and in alloimmune graft-versus-host disease (GVHD) and hepatic allograft rejection. The onset of NSDC in the B10.D2→BALB/c murine model of hepatic GVHD is preceded by hepatic production of pro-inflammatory cytokines, accumulation of lipopolysaccharide (LPS), and expression of chemokine genes. To explain the curious restriction of NSDC to small- and medium-caliber intrahepatic bile ducts, we hypothesized that BEC lining these bile ducts secrete chemokines and cytokines that chemoattract, activate, and polarize the effector T cells mediating NSDC. To test this hypothesis we stimulated BALB/c immortalized BEC (IBEC) in vitro with pro-inflammatory mouse recombinant cytokines with and without LPS and determined the expression of chemokines and cytokines by IBEC using a polymerase chain reaction (PCR), quantitative protein enzyme-linked immunosorbent assays (ELISAs), and microarrays. The capacity of stimulated IBEC to chemoattract activated T cells was assessed in the presence and absence of inhibitors of specific chemokine receptors. We found that pro-inflammatory cytokines, especially the combination of IFNγ and TNFα, induced IBEC gene expression and the secretion of chemokine ligands for the chemokine receptors CCR1, CCR3, CCR5, and CXCR3. Chemokines secreted by IBEC stimulated with IFNγ plus TNFα chemoattracted activated T cells. Inhibition of CCR1, CCR3, CCR5, or CXCR3 significantly reduced the chemoattraction of activated T cells. We conclude that BEC probably play an active role in the immunopathogenesis of NSDC by mediating the chemoattraction and terminal activation of effector T cells responsible for apoptosis of BECs and ductopenia. Selective chemokine expression by BEC lining small- and medium-caliber bile ducts could explain the restriction of NSDC to ducts of this caliber. Inhibition of CCR1, CCR3, CCR5, and CXCR3 to block the chemoattraction and terminal activation of alloreactive T cells represents a potential therapeutic strategy for preventing NSDC after hematopoietic stem-cell transplantation or orthotopic liver transplantation.