NF-kappaB activation and zinc finger protein A20 expression in mature dendritic cells derived from liver allografts undergoing acute rejection.

Abstract

To investigate the role of NF-kappaB activation and zinc finger protein A20 expression in the regulation of maturation of dendritic cells (DCs) derived from liver allografts undergoing acute rejection. Sixty donor male SD rats and sixty recipient male LEW rats weighing 220-300 g were randomly divided into whole liver transplantation group and partial liver transplantation group. Allogeneic (SD rat to LEW rat) whole and 50 % partial liver transplantation were performed. DCs from liver grafts 0 hour and 4 days after transplantation were isolated and propagated in the presence of GM-CSF in vitro. Morphological characteristics and phenotypical features of DCs propagated for 10 days were analyzed by electron microscopy and flow cytometry, respectively. NF-kappaB binding activity, IL-12p70 protein and zinc finger protein A20 expression in these DCs were measured by EMSA and Western blotting, respectively. Histological grading of rejection was determined. Allogeneic whole liver grafts showed no signs of rejection on day 4 after the transplantation. In contrast, allogeneic partial liver grafts demonstrated moderate to severe rejection on day 4 after the transplantation. After propagation for 10 days in the presence of GM-CSF in vitro, DCs from allogeneic whole liver grafts exhibited features of immature DC with absence of CD40 surface expression, these DCs were found to exhibit detectable but very low level of NF-kappaB activity, IL-12 p70 protein and zinc finger protein A20 expression. Whereas, DCs from allogeneic partial liver graft 4 days after transplantation displayed features of mature DC, with high level of CD40 surface expression, and as a consequence, higher expression of IL-12p70 protein, higher activities of NF-kappaB and higher expression of zinc finger protein A20 compared with those of DCs from whole liver grafts (P<0.001). These results suggest that A20 expression is up-regulated in response to NF-kappaB activation in mature DCs derived from allogeneic liver grafts undergoing acute rejection. Given the NF-kappaB inhibition function of this gene, it is suggested that their expression survives to limit NF-kappaB activation and maturation of DCs, and consequently inhibits the acute rejection and induces acceptance of liver graft.