Acute rejection in the absence of cognate recognition of allograft by T cells

We studied the effects of the indirect pathway of allograft recognition using T cells from TCR transgenic Marilyn mice, which recognize the male Ag H-Y in an I-A(b)-restricted fashion. The T cells are not alloreactive to the H-2(k) haplotype, because they are not activated when adoptively transferred into recombinase-activating gene-2(-/-) common gamma-chain(-/-) double-mutant H-2(k) male or female mice. However, skin from H-2(k) males, but not from H-2(k) females, is acutely rejected by recombinase-activating gene-2(-/-) transgenic female recipients. In vitro, Marylin spleen cells primed by H-2(k) skin grafting proliferated and secreted both IL-4 and IFN-gamma in response to H-2(k) male stimulators. However, the removal of H-2(b) APC from the responding population abolished the response. Taken together, these results show that the indirect recognition that triggers rejection in this model is due to the recognition of H-Y Ag shed from H-2(k) male allograft and presented by the recipient's own I-A(b) APC to transgenic T cells. This study demonstrates unequivocally the capacity of naive CD4(+) T cells to promote the rejection of allografts through mechanisms that involve indirect destruction of grafted tissues.     

Cellular immunity in allograft rejection: role of lymphocyte subpopulations and T-cell subsets in rat cardiac allograft rejection

In this study, cellular requirements for rejection are examined by the use of adoptive transfer assays in the ACI to Lewis cardiac allograft model. The findings show that adoptive transfer of 1 x 10(8) spleen cells (SpL), 5 x 10(7) T-cells, and 2 x 10(7) helper T-cells (W3/25+) obtained from normal, nonsensitized donors restores acute ACI graft rejection in sublethally irradiated (750 rad) Lewis recipients. In contrast, reconstitution with 2 x 10(7) cytotoxic T-cells (0X8+) does not restore first-set graft rejection. Reconstitution of the irradiated recipients with either W3/25+ or 0X8+ T-cells obtained from specifically sensitized syngeneic donors resulted in acute rejection. The W3/25+ T-cell subset was significantly more potent (P less than 0.01) in effecting rejection on a per-cell basis. Adoptive transfer of SpL, T-cells, and 0X8+ T-cells obtained from sensitized rats led to accelerated cardiac allograft rejection in the naive secondary recipients while W3/25+ T-cells did not. This study suggests that although the W3/25+ T-cells alone have the capacity to initiate first-set graft rejection, both W3/25+ and 0X8+ subsets appear to be critical to the completion of rejection of heart allografts. We also examined the capacity of adoptively transferred B-cells from sensitized donors to influence graft rejection. Our findings suggest that while B-cells fail to restore the capacity for graft rejection in irradiated recipients, they can, however, present MHC antigens to the secondary naive host thus causing allosensitization which results in accelerated rejection of a subsequent graft.     

Mechanism of thyroid allograft rejection.

Balb/c thyroids, held in organ culture for 26 days, survive and function as well as isografts for greater than 100 days in CBA recipients. Uncultured allografts are totally rejected by 20 days after transplantation. Prolonged allograft survival can also be achieved by the treatment of donor animals with cyclophosphamide prior to harvesting tissues for transplantation. These allografts do not survive as well as 26 day cultured allografts, but cyclophosphamide pretreatment reduces the culture time required to achieve indefinite survival to 7 days. The provision of an allogeneic (LD) stimulus by thyroid tissue that is I-region incompatible with the host does not facilitate the rejection of a tolerated cultured allograft. However, activation of the host immune system by an uncultured graft syngeneic to a tolerated cultured allograft leads to the chronic rejection of the cultured transplant. The transfer of a tolerated cultured allograft back to its strain of origin induces an acute inflammatory reaction that causes tissue damage within the transplant but does not lead to the total destruction of the tissue.     

Analysis of cytokine dynamics in corneal allograft rejection

Motivated by the discovery of oscillations in tumour necrosis factor-alpha (TNF-alpha) concentration in the aqueous humour of rabbits undergoing corneal allograft rejection, a simple mathematical model is developed for the regulation of TNF-alpha, which incorporates both negative feedback and amplification pathways. Mathematical analysis reveals a surprisingly rich behavioural repertoire for this simple cytokine pathway, including excitability, threshold behaviour, hysteresis, oscillations and bistability. This suggests new possibilities for experimental demonstration, and reveals the potential contributions of nonlinear dynamics to understanding cytokine regulation.     

HLA-DRw6 and renal allograft rejection.

HLA-DRw6-positive patients are "high responders" to certain renal allograft antigens. A study was therefore conducted of the outcome of 247 first renal allografts in 74 DRw6-positive and 173 DRw6-negative recipients. The effectiveness of matching for HLA-DR determinants in both groups was also analysed. The one-year graft survival in DRw6-positive patients was 59% as compared with 75% in DRw6-negative recipients (p = 0.012). A striking difference between the two groups was that HLA-DR matching significantly improved renal allograft survival only in the DRw6-positive patients. In those patients the one-year survival of HLA-DR-identical grafts was 95% as compared with only 38% for 2-DR mismatched grafts (p = 0.009). In DRw6-negative patients only a slight beneficial effect of HLA-DR matching was observed (83% versus 72% at one year for the 0-DR and 2-DR mismatched grafts, respectively) (p greater than 0.05). These findings are clear evidence that DRw6-positive patients (about a quarter of the patients on the waiting list of Eurotransplant) should be given HLA-DR-identical kidney transplants only.     

The role of TNF-related activation-induced cytokine-receptor activating NF-kappa B interaction in acute allograft rejection and CD40L-independent chronic allograft rejection

We analyzed the role of TNF-related activation-induced cytokine (TRANCE), a member of the TNF family expressed on activated T cells that shares functional properties with CD40L, and its receptor-activating NF-kappaB (RANK) which is mostly expressed on mature dendritic cells, during allogenic responses in vivo using a rodent heart allograft model. TRANCE mRNA was strongly up-regulated in acutely rejected allografts on days 4 and 5 posttransplantation whereas RANK was detected as early as day 1 but did not show further up-regulation during the first week. Immunofluoresence analyses of heart allografts showed that 80 and 100% of TRANCE and RANK-expressing cells were T cells and APCs, respectively. We show for the first time that short-term TRANCE blockade using a mouse RANKIg fusion molecule can significantly prolong heart allograft survival in both rat and mouse models. Similarly, rat heart allografts transduced with a RANKIg encoding recombinant adenovirus exhibited a significant prolongation of survival (14.3 vs 7.6 days, p < 0.0001). However, TRANCE blockade using RANKIg did not appear to inhibit allogeneic T and B cell priming humoral responses against RANKIg. Interestingly, TRANCE blockade induced strong up-regulation of CD40 ligand (CD40L) mRNA in allografts. Combined CD40L and TRANCE blockade resulted in significantly decreased chronic allograft rejection lesions as well as allogeneic humoral responses compared with CD40L blockade alone. We conclude that TRANCE-RANK interactions play an important role during acute allograft rejection and that CD40L-independent allogeneic immune responses can be, at least in part, dependent on the TRANCE pathway of costimulation.     

Induction of allograft tolerance in the absence of Fas-mediated apoptosis.

Using certain immunosuppressive regimens, IL-2 knockout (KO) mice, in contrast to wild-type (wt) controls, are resistant to the induction of allograft tolerance. The mechanism by which IL-2 regulates allograft tolerance is uncertain. As IL-2 KO mice have a profound defect in Fas-mediated apoptosis, we hypothesized that Fas-mediated apoptosis of alloreactive T cells may be critical in the acquisition of allograft tolerance. To definitively study the role of Fas in the induction of transplantation tolerance, we used Fas mutant B6.MRL-lpr mice as allograft recipients of islet and vascularized cardiac transplants. Alloantigen-stimulated proliferation and apoptosis of Fas-deficient cells were also studied in vivo. Fas mutant B6.MRL-lpr (H-2b) mice rapidly rejected fully MHC-mismatched DBA/2 (H-2d) islet allografts and vascularized cardiac allografts with a tempo that is comparable to wt control mice. Both wt and B6.MRL-lpr mice transplanted with fully MHC-mismatched islet allografts or cardiac allografts can be readily tolerized by either rapamycin or combined costimulation blockade (CTLA-4Ig plus anti-CD40L mAb). Despite the profound defect of Fas-mediated apoptosis, Fas-deficient T cells can still undergo apoptotic cell death in vivo in response to alloantigen stimulation. Our study suggests that: 1) Fas is not necessarily essential for allograft tolerance, and 2) Fas-mediated apoptosis is not central to the IL-2-dependent mechanism governing the acquisition of allograft tolerance.     

Detection of renal allograft rejection by computer.

A computer program incorporating an adaptation of a statistical method, the multiprocess Kalman filter, was used to detect changes in trends of plasma creatinine and urea concentrations. In 28 recipients of renal allografts a definite deterioration in renal function was identified retrospectively on 32 occasions by an experienced renal physician independently of the statistical analysis. The computer identified 31 of these 32 episodes using creatinine and urea results, and 29 using creatinine alone. Dysfunction was identified by the computer significantly earlier (p less than 0.05) than by the clinician and a median of one day earlier (p less than 0.02) than treatment was actually initiated. The computer identified dysfunction on 11 out of 1259 days when the clinician did not suspect rejection. These 11 episodes may have had a pathological importance, though no clinical diagnosis was made. This computer method is useful for immediate analysis of incoming results and for timing events either prospectively or retrospectively.     

T cell receptor beta-chain selection in human allograft rejection

We have analyzed a series of T cell lines established from renal needle biopsies taken from renal allograft recipients with clinical signs of rejection. These T cells show strong cytotoxicity directed against donor HLA and their proliferative capacity in vitro is highly correlated with irreversible graft rejection. A total of 10 of 12 lines examined by Southern blot analysis using a J beta C beta DNA probe show predominant beta-chain rearrangements. In one instance DNA was isolated from cell lines generated from sequential biopsies taken from the same patient at different times of rejection. These lines show the same predominant beta-chain rearrangements. To determine whether these predominant rearrangements are due to expansion of a single clone or different T cell clones rearranging similar beta-chains, the same blots were analyzed with a J gamma probe. Cell line MH3 shows two predominant beta-chain rearrangements and at least seven of eight possible rearranged gamma-chain bands, implying that multiple clones share similar beta-chains. In contrast, the cell line King shows a single beta-chain and a single gamma-chain rearrangement. Many of the other cell lines fall between these two extremes, indicating that both beta-chain selection and clonal dominance are operating during graft rejection, resulting in the appearance of predominant beta-chain rearrangements.     

The innate immune system in allograft rejection and tolerance

As T cells alone are both necessary and sufficient for the rejection of virtually all allogeneic tissues, much of transplantation immunology has focused on cells of the adaptive immune system. During the past decade, advances in our understanding of innate responses to pathogen-associated molecules have spurred a "rediscovery" of innate immunity. Fueled by this, an increasing body of literature has emerged in which the role of the innate immune system in allograft rejection and tolerance has been examined more closely. This review will give an overview of recent studies and emerging concepts of how the cellular components of the innate immune system participate in the immune response to solid organ transplantation. These important studies highlight the complex interplay between diverse cells of the immune response and provide the basis for optimal strategies of tolerance induction.     

Involvement of lymphocyte mediators in the rejection of a murine tumor allograft

Macrophage migration inhibition by peritoneal leukocytes was studied in BALB/c mice bearing intraperitoneal allogeneic EL-4 lymphomas to explore the role of this immune effector function in allograft rejection. The nonadherent peritoneal leukocyte population harvested between 8 and 10 days after allograft inoculation inhibited migration of nonimmune murine macrophages as demonstrated by both direct and indirect migration assays using the agarose droplet method. This host response also contained large numbers of adherent macrophages which others have shown to be cytotoxic to EL-4 target cells. These findings provide direct evidence for lymphokine activity in allograft rejection and suggest that lymphocyte mediators may attract and activate the cytotoxic macrophages observed in this response.