Abrogation of the immunosuppressive effect of donor spleen cells on renal allografts in the rat by irradiation or heat treatment

Application of popliteal lymph node assay to evaluate tolerogenic effect of donor leukocyte infusion

BACKGROUND

Popliteal lymph node assay (PLNA) has long been proposed to detect immunostimulating potential of chemicals. Here, the PLNA was used to evaluate the effect of donor leukocyte infusion on recipients' reaction to donor-specific antigens.

METHODS

Donor rats' peripheral blood leukocytes (ranging from 1 x 10(4) to 500 x 10(4) cells) were intravenously (i.v.) infused into recipients. A week later recipients' reaction to donor-specific antigen was evaluated, using the PLNA technique, by subcutaneous injection of donor spleen cells to one hind footpad of recipients and injection of saline to the other. Seven days later all recipients were killed and their PLNs' weight and cellularity indices were determined. While the same process was applied to the positive control (PC) animals, rats without leukocyte infusion, negative control (NC) animals, rats without leukocyte infusion, were injected in both hind footpads with saline.

RESULTS

The PLN weight indices of recipients of: > or =5 x 10(4) leukocytes were significantly lower than PC animals (P < 0.001), whereas the weight indices of recipients of 1 x 10(4) cells were similar to PC group but higher than NC animals (P < 0.0001). However, the PLN cellularity indices of recipients of < or =10 x 10(4) cells were not different from PC animals but the PLN cellularity indices of recipients of: > or =50 x 10(4) cells were significantly lower than PC group (P < 0.05).

CONCLUSION

Overall, these results suggest that donor leukocytes infusion dose-dependently decrease reaction to donor-specific antigens, but a state of tolerance to donor antigen might be induced at the dose of: > or =50 x 10(4) cells. PLNA appears to represent a simple test model to quantify efficacy of immunotolerance protocols.

Postoperative administration of donor B cells induces rat kidney allograft acceptance: lack of association with Th2 cytokine expression in long-term accepted grafts

BACKGROUND

Although donor leukocytes are only thought to prolong survival when administered before transplantation, recent evidence shows that they are effective at transplantation. This study aims to identify the leukocyte subset that is most active in prolonging kidney allograft survival and examine the cytokine expression in long-term acceptance.

METHODS

PVG rat kidneys were transplanted to completely MHC class I and class II-mismatched DA recipients. Donor B cells or T cells, purified by negative selection, were injected i.v. at the time of transplantation. Expression of interleukin (IL)-2, IL-4, IL-10, interferon (IFN)-gamma, and transforming growth factor-beta mRNA was measured by quantitative real-time polymerase chain reaction (PCR). Immunohistochemical analysis and terminal deoxynucleotide transferase-mediated dUTP nick-end labelling (TUNEL) staining was used to identify infiltrating cells and apoptotic cells, respectively, in sections of kidney allografts.

RESULTS

Median kidney graft survival time (MST) of B cell-treated animals (n=5) was >300 days, compared with 7 days in untreated animals (n=7) (P=0.003), whereas animals treated with the same number of T cells (n=6) had a MST of 17 days (P=0.1 vs. untreated, P=0.03 vs. B cell-treated). Examination of the long-term (>300 days) accepted grafts from B cell-treated recipients showed little evidence of kidney damage but a moderate perivascular infiltrate consisting of T and B cells. This infiltrate seemed to be quiescent because there was no detectable expression of IL-2 receptors or of apoptotic cells. It produced little or no cytokine mRNA, because expression in the long-term accepted grafts was similar to levels in normal kidneys or syngeneic transplants. There was a marked increase of cytokine mRNA early after transplantation in both leukocyte-treated and untreated grafts, with more rapid appearance of IFN-gamma and IL-10 in leukocyte-treated grafts.

CONCLUSIONS

Donor B cells efficiently induce long-term acceptance of transplanted kidneys in a fully MHC-mismatched rat model when administered at transplantation, by a mechanism that seems to be independent of Th2 cytokine expression within the long-term accepted graft.

Antigen-Induced Unresponsiveness Results in Altered T Cell Signaling

Pretransplant exposure to allogeneic lymphocytes can result in donor-specific unresponsiveness and prolonged allograft survival. Intracellular signaling events have been described in anergic T cell clones, but the biochemical events underlying in vivo induced unresponsiveness have not been studied in detail. We employed a TCR transgenic mouse, bearing the 2C TCR, providing adequate numbers of homogenous peripheral T cells to study biochemical aspects of T cell unresponsiveness in vivo. 2C mice exposed to semiallogeneic lymphocytes (H-2b × H-2d) experienced prolonged H-2d cardiac allograft survival, and cells from these mice did not proliferate or make IL-2 in response to alloantigen (H-2d). Importantly, there were marked differences in TCR-associated tyrosine phosphorylation activation patterns. The targets for the unresponsive state appear to be diminished Lck activation and absent ZAP-70 and LAT (linker for activation of T cells) phosphorylation. Our study demonstrates that Ag-induced tolerance in vivo is accompanied by altered early TCR-mediated signaling events.

Injection of mitomycin-C-treated spleen cells induces donor-specific unresponsiveness to cardiac allografts in rats

BACKGROUND

In this study, preoperative mitomycin-C- (MMC) treated donor-specific transfusion (DST) was examined for its ability to induce unresponsiveness to cardiac allografts in rats.

METHODS

DA (RT1a) rats were used as donors, BUF (RT1b) or WS (RT1k) rats as recipients, and Lew (RT1l) rats as third party donors. BUF or WS rats were given i.v. injection of DA spleen cells (SPCs) suspension (5x10(7)/l ml) with or without MMC treatment 10 days before cardiac transplantation. Delayed-type hypersensitivity and complement-dependent cytotoxicity assays were carried out in these animals separately to examine in vivo immunosuppressive effect. Suppressor assay was also examined to determine in vitro immunosuppressive effects in allogeneic mixed leukocyte culture.

RESULTS

In the full allogeneic DA-to-BUF rat strain combination, preoperative i.v. administration of MMC-treated donor SPCs led to a significant prolongation of graft survival over the control (110+/-66 versus 7.2+/-0.8 days: P<0.01), although administration of nontreated donor SPCs did not (9.3+/-1.0 days). This beneficial effect of MMC treatment was also seen in the DA-to-WS rat combination (31+/-16 days versus donor-specific transfusion alone; 11+/-1.5 days or untreated control; 12+/-1.5 days; P<0.05). However, injection of third party DA SPCs in the Lew-to-BUF combination induced no significant prolongation of cardiac allograft survival compared with the untreated control (11+/-0.6 versus 11+/-2.0 days; NS), indicating that this prolongation effect was induced in an antigen-specific manner. The immunosuppressive effect was also secured for both delayed-type hypersensitivity response and anti-donor cytotoxic antibody production. Moreover, addition of MMC-treated SPCs to mixed lymphocyte culture led to antigen-specific suppression.

CONCLUSIONS

Preoperative i.v. injection of MMC-treated donor SPCs is promising for inducing unresponsiveness in rat cardiac allograft model.

Tolerance to rat liver allografts: IV. Acceptance depends on the quantity of donor tissue and on donor leukocytes

Liver allografts in some rat strains are often spontaneously accepted across a complete major histocompatibility barrier without the requirement for immunosuppression while other nonliver allografts are rejected. In previous studies, we have shown that spontaneous acceptance is dependent on liver passenger leukocytes. Depletion of passenger leukocytes by donor irradiation allows rejection, with DA recipients of irradiated PVG livers having a median survival time (MST) of 16 days. Here we show that, in this model, spontaneous acceptance is reconstituted by intravenous injection of donor leukocytes. Intravenous injection of 3-5x10(7) PVG liver leukocytes significantly prolonged DA survival time (MST=96 days, P=0.026), as did 5x10(7) spleen leukocytes (MST>100 days, P=0.002). Deletion of T cells from the reconstituting inoculum reduced survival time (MST=78 days, P=0.039), whereas deletion of B cells or monocytes/macrophages had no effect on survival time. In contrast, PVG hearts are regularly rejected by DA recipients, and PVG liver or spleen leukocytes, even at doses of greater than 3x10(8) cells/recipient, were unable to induce heart acceptance. To investigate the possibility that acceptance of the irradiated liver but not the heart might be due to the large mass of the liver, two kidneys and two hearts of PVG origin were transplanted to each DA recipient together with 1.5x10(8) PVG leukocytes. These organs survived for greater than 200 days, thereby showing that a large mass of donor tissue, in association with donor leukocytes, leads to acceptance of organs that are rejected if transplanted singly. It appears likely that spontaneous liver transplant tolerance is a high-dose or activation-associated immune phenomenon.

Induction of transplantation tolerance by intravenous injection of allogeneic lymphocytes across an H-2 class II mismatch. Different mechanisms operate in tolerization across an H-2 class I vs. H-2 class II disparity

Previously, we have shown that the intravenous (i.v.) injection of allogeneic lymphocytes across an H-2 class I-mutant disparity leads to specific skin allograft tolerance caused by irradiation-sensitive donor T cells, which function as veto cells. In the present study, we show that the i.v. injection of H-2 class II-incompatible spleen cells also results in specific skin allograft tolerance. However, tolerance induction depends on the presence of irradiation-resistant non-T cells in the donor cell inoculum. Thus, different mechanisms operate in tolerance induction across an H-2 class I vs. H-2 class II mismatch. I.v. injection of allogeneic spleen cells across an H-2 class I plus class II disparity does not result in skin allograft tolerance. Finally, our data show that transfusion-induced suppression of the delayed-type hypersensitivity response against alloantigens does not correlate with skin allograft tolerance induced by i.v. injected allogeneic lymphocytes. In conclusion, the type of H-2 mismatch between transfusion donor and recipient not only determines the occurrence of allograft tolerance but also the mechanism leading to tolerization.

Induction of allograft tolerance to the H-Y antigen in adult C57BL/6 mice: differential effects on delayed-type hypersensitivity and cytolytic T-lymphocyte activity

This study describes the induction of allograft tolerance to the "male-specific," minor histocompatibility antigen, H-Y, in adult C57BL/6 female mice, and the effects of this tolerance induction on two immune parameters associated with graft rejection: delayed-type hypersensitivity (DTH) and cytolytic T-lymphocytes (CTL). B6 females tolerized to H-Y, by a single iv injection of C57BL/6 male lymphocytes, exhibited prolonged or permanent survival of B6 male tail skin grafts. Graft-induced DTH against H-Y antigen was reduced or abrogated in tolerized females. Delayed onset of graft rejection in partially tolerant females correlated with delayed onset of DTH, and eventual rejection of grafts was accompanied by an increase in H-Y-specific DTH. In contrast, H-Y-specific CTL activity was not consistent with graft status. These data demonstrate a correlation between H-Y-specific DTH and rejection of male skin grafts by B6 female mice and are most consistent with a major effector role for DTH in chronic graft rejection.

Veto function in vitro and in vivo

A CTLp recognizing another cell, called veto cell, is suppressed by that veto cell. The veto cell can itself be a CTL. For the veto function, the TCR of the veto cell is not required, hence the veto function is a backward action of CTL. Since, from the point of view of the veto cell, only self-reactive CTLp are suppressed, the veto function could be a mechanism for maintaining self tolerance of CTL. The characteristics of veto function in vitro and in vivo are discussed, as well as the potential physiological relevance.

Splenectomy and renal allograft survival in the rat

The effect of splenectomy on renal allograft survival is not clear. In the rat, spleens isolated from recipients with functioning grafts have been shown to be a major source of cells that are capable of suppressing the rejection response (suppressor T lymphocytes). Thus the removal of the spleen in these allograft recipients could be detrimental to renal allograft survival. This study investigates this hypothesis, and looks for the presence of suppressor cells in other lymphoid organs apart from the spleen. In the rat renal allograft model, donor Lewis spleen cells given to DA recipients intravenously 1 week before transplantation of a Lewis kidney leads to indefinite allograft survival (median survival time (MST) greater than 100 days). Splenectomy before or after pretreatment with donor spleen cells failed to abrogate this effect (MST greater than 100 days). Experiments were performed in which cells or serum were prepared from long-term surviving splenectomized animals which had already been pretreated and transplanted, and then were injected into untreated recipients (adoptive transfer experiments). This was done to determine if cells capable of suppressing graft rejection were present in lymphoid organs outside the spleen in these splenectomized recipients. Thus the IV transfer of 10(8) lymph node cells harvested from splenectomized DA recipients with a long-term surviving LEW graft (LTS), into untreated but lightly irradiated (200 rad) DA recipients resulted in indefinite survival of a fresh Lewis kidney (MST greater than 100 days). In contrast, adoptive transfer of normal DA lymph node cells was ineffective (MST 13 days). Thus splenectomy is not necessarily detrimental to graft survival, as cells capable of preventing graft rejection are found in other lymphoid organs, such as lymph nodes, in splenectomized recipients.