Prolongation of discordant heart xenograft survival after liver hemoperfusion: role of nonparenchymal liver cells

Role of Kupffer cells in the induction of tolerance of orthotopic liver transplantation in rats

Because the role of Kupffer cells (KCs) in liver transplantation (LT) tolerance is not well understood, we investigated their role in liver allograft acceptance in rats. Male Sprague-Dawley rats were randomly assigned to either an LT group or a transplantation group pretreated with GdCl(3) (Gd group). The rats were postoperatively sacrificed at indicated times for histology and assessment of KC function, nuclear factor kappa B (NF-kappaB) activity, and cytokine production. KCs and T cells (TCs) were isolated from allografts to assess Fas/Fas ligand (FasL) expression. Cytotoxicity of KCs against TCs was monitored by coculturing of (3)H-thymidine TCs with KCs at various effector-to-target ratios. The results were as follows. First, grafts were spontaneously accepted in the LT group with evident apoptosis of TCs; however, inhibition of KCs by pretreatment with GdCl(3) decreased TC apoptosis and shortened the survival of allografts. Second, KCs in the LT group had increased levels of FasL messenger RNA and protein with respect to that in the Gd group. Third, by in vitro cocultivation assays, KCs induced TC apoptosis though elevated expression of FasL, and this process could be blocked by anti-FasL antibody. Fourth, there was a positive correlation between activation of NF-kappaB and FasL expression in KCs and interleukin-4 production in the LT group, and the activation of NF-kappaB was inhibited by pretreatment with GdCl(3). In conclusion, KC-induced depletion of TCs via the Fas/FasL pathway might play a critical role in LT tolerance. However, the tolerance is abrogated by suppression of FasL and IL-4 expression via inhibition of NF-kappaB activity by GdCl(3).

The protective role of Kupffer cells in humoral injury of xenoperfused rat livers

BACKGROUND

The role of Kupffer cells in a hepatic xenograft rejection is still unclear. We investigated the effect of blocking Kupffer cells on xenogeneic humoral injury using rat livers as the xenoperfusion models.

METHODS

Rat livers were perfused with fresh human blood after pretreatment either with normal saline (group 1; n = 8) or with gadolinium chloride (GdCl3) solution (group 2; n = 8). Tissue injury was evaluated by alanine aminotransferase release and histological examination. Tumor necrosis factor-alpha (TNF-alpha) production from rat livers was measured by enzyme-linked immunosorbent assay and also examined by immunohistochemistry. In addition, Kupffer cells were isolated after pretreatment either with normal saline or with GdCl3 solution and incubated with human serum. Localization of human C3 and IgM was examined by immunofluorescence.

RESULTS

Alanine aminotransferase release in group 2 was significantly higher than in group 1 (P = 0.015). Histological examination revealed more severe tissue injury in group 2. The mean TNF-alpha level was not significantly different between the two groups. In immunohistochemistry, TNF-alpha was positive primarily on vascular endothelial cells in both groups. Immunofluorescence of saline-treated Kupffer cells showed an uptake of human C3 in the cytoplasm, whereas no uptake was observed in GdCl3-treated cells. The uptake of human IgM did not differ between the two groups.

CONCLUSIONS

These results suggest that Kupffer cells have a protective role in preventing xenogeneic humoral injury. Their ability to absorb xenogeneic complements may contribute to this protective mechanism.