Restoration of tolerance to rat hepatic allografts by spleen-derived passenger leukocytes

Abstract

The tolerance induced by orthotopic liver transplantation (OLT) in certain combinations of rat strains can be prevented by total body irradiation (TBI) of the donor. We demonstrate here that the intravenous inoculation of splenic leukocytes into irradiated donors before OLT could re-establish tolerance in association with a state of microchimerism detected in the recipients. When donor DA (RT1a) strain rats were irradiated with 1000 rad 24 h before liver harvesting and subsequent liver implantation into PVG recipients, five out of six rats died from rejection in this normally tolerogenic OLT (DA-PVG) combination. Injection of 1.5 x 10(8) splenic leukocytes from naive DA rats into the irradiated DA donor rats 24 h before OLT restored the tolerogenic potential of the liver allografts. Immunofluorescence assay revealed an increased number of donor (DA) type cells in the PVG recipient bearing a repopulated DA liver, compared to the PVG recipient of an irradiated liver. These results suggest that passenger leukocytes reconstituted by splenic leukocytes have the capacity to protect liver allografts.

The characterization of reconstituted passenger leukocytes on the induction of tolerance in rat liver transplantation

“…However, TBI (1000 rads) of DA donor rats 24 h prior to OLT prevented the induction of tolerance in PVG recipients [26], as shown in our group 3 (Table 1). Group 2 showed that graft viability was not affected by irradiation.…”

“…Using a naturally tolerogenic combination of rats in OLT, we have demonstrated, as have others [29], that TBI of the donor fails to induce tolerance in these recipients. However, unlike other studies using parking of the liver [27, 291, reconstitution of the irradiated donor with bone marrow cells [31], or injection of cells into the recipient, we reestablished liver-induced tolerance simply by injecting naive donor type spleen cells into the irradiated donor 24 h prior to transplantation [26]. Furthermore, our present study shows that splenic "T-cell-enriched" populations may play an important role in the restoration of liver graft acceptance, although we should further investigate the involvement of radio-resistant dendritic cells [8,29] or intrahepatic hematopoietic stem cells [2,20] in the induction of tolerance.…”

Differences in the rate of donor leucocyte migration between natural and drug-assisted tolerance following rat liver transplantation

“…It therefore may well be possible that a specific number of donor leucocytes is required to migrate to a given recipient organ for tolerance to be achieved. Indirect evidence to support this contention has recently been reported by Shimizu et al [17]. The investigators in this study have shown that if a PVG recipient that has been transplanted with an irradiated DA liver received 1 : 5 × 10 8 DA splenocytes following OLT then tolerance is maintained.…”

“…This transplant phenomenon has been described in some detail, and is observed following both clinical transplantation [1][2][3][4][5][6][7][8][9] and in experimental animal models [10][11][12][13][14][15][16][17]. It has also been shown to occur regardless of whether immunosuppressive drugs are used as in the clinical situation [1][2][3][4][5][6][7][8][9] and in the absence of immunosuppression, as is the case for some animal models involving liver transplantation [11][12][13][14][15].…”

“…Absence of a chimerism from these sites is by no means indicative of chimerism being not present in other tissues, in particular lymphoid organs such as the spleen and as seen in animal models [11,14,15,17]. Thus the recipient organs biopsied following transplantation are very important in evaluating this process, and this has been recently restressed in the literature [18].…”