Lymphocyte migration patterns in organ allograft recipients

SPECT/CT lymphoscintigraphy of heterotopic cardiac grafts reveals novel sites of lymphatic drainage and T cell priming

The normal function of lymphatic vessels is to facilitate the trafficking of antigen presenting cells to draining lymph nodes where they evoke an immune response. Donor lymphatic vessels are not connected to that of recipients' during organ transplantation. The pathophysiology of this disruption has received little attention. Murine heterotopic cardiac transplantation has been used extensively in transplantation research. Following vascularized organ transplantation, the main site of allosensitization is thought to be in the spleen of the recipient as a result of migration of donor passenger leukocytes via blood. Here, using Single Photon Emission Computed Tomography/Computerized Tomography (SPECT/CT) lymphoscintigraphy, we studied the pattern of lymphatic flow from mouse heterotopic abdominal cardiac grafts and identified mediastinal lymph nodes as the draining nodes for the donor graft. Staining with HY tetramer after transplantation of HY mismatched heart grafts and ELISPOT following allogeneic grafts to detect donor specific T cells revealed them as important sites for allosensitization. Our data indicates that mediastinal lymph nodes play a crucial role in the alloimmune response in this model, and should be used for ex vivo and adoptive transfer studies after transplantation in addition to the spleen.

Effect of combined treatment with FK506, FTY720, and ex vivo graft irradiation in rat small bowel transplantation: expression of mucosal addressin cell adhesion molecule-1

We studied the effect of the combined treatment with FK506, FTY720, and ex vivo graft irradiation. Five groups of SBT animals were studied on days 3, 5, and 7 after operation (untreated, FK506, FTY720, FK506 + FTY720, FK506 + FTY720 + irradiation). Indirect immunoperoxidase staining was performed against CD4 and MAdCAM-1. The numbers of CD4 positive cells in allografts were also analyzed by flow cytometry. The graft survival was prolonged in all of the FK506- and FTY720-treated groups. SBT allografts treated by FK506 and FTY720 demonstrated less infiltration of CD4 positive cells, but the irradiation group did not show any effects on its expression. In FK506- and FTY720-treated groups, MAdCAM-1 expression on the HEVs in PPs was up-regulated, and its expression on the ECVs in the LP was down-regulated compared with other allograft groups. Irradiation did not show any effects on MAdCAM-1 expression on both HEVs in PPs and ECVs in LP. FK506 and FTY720 prevented the infiltration of CD4 positive cells, the down-regulation of MAdCAM-1 expression on HEVs in PPs, and the up-regulation of MAdCAM-1 expression on ECVs in LP during the early phase of SBT.

Effect of FTY720 in rat small bowel transplantation: expression of mucosal addressin cell adhesion molecule-1

AIM

Mucosal addressin cell adhesion molecule-1 (MAdCAM-1) mediates the homing of lymphocytes to gut-associated tissues (GALT). We performed a semiquantitative analysis of MAdCAM-1 expression during small bowel graft rejection in rat treated with FTY720.

METHODS

Orthotopic small bowel transplantations (SBT) were performed from BN rats to LEW rats. Isografted animals served as controls. Three groups of SBT animals were studied on days 3, 5, 7 after operations (Isograft, untreated allograft, allograft with FTY720). FTY720 was orally administered by gavage (1 mg/kg/d) to allograft models on 7 consecutive days. Cryostat sections were prepared from grafts, including Peyer's patches (PPs). Indirect immunoperoxidase staining was performed using mAbs against MAdCAM-1. The degree of vascular endothelial staining on high endothelial venules (HEV) in the PPs was graded from 1 (low levels) to 5 (high levels), and in the vessels of the lamina propia from 1 (faint), to 2 (low at the base of villi), 3 (low to the middle of villi), 4 (high to the middle of villi), to 5 (high to villi tip).

RESULTS

The graft survival was prolonged in the FTY720-treated group. MAdCAM-1 expression on HEVs in PPs was down-regulated during rejection. In contrast its expression on endothelial cells of vessels in the lamina propria was up-regulated during rejection. In the FTY720-treated groups, MAdCAM-1 expression on HEVs in PPs was up-regulated and its expression on endothelial cells of vessels in the lamina propria was down-regulated compared with untreated allograft group.

CONCLUSIONS

Alteration in MAdCAM-1 expression may be associated with the development of SB graft rejection. The vessels at the base of villi, which are associated with lymphocyte recruitment, may become sites of intestine immune reactivity during the early phase of small bowel allograft rejection. FTY720 was found to prevent the down-regulation of MAdCAM-1 expression on HEVs in PPs and the up-regulation of its expression on endothelial cells of vessels in the lamina propria while also prolonging small bowel allograft survival.

Rejection following donor or recipient preoperative treatment with FTY720 in rat small bowel transplantation

BACKGROUND

Severe rejection of small bowel transplantation (SBTx) has been ascribed to abundant lymphoid tissues in the small intestine without well-established evidence. However, the role of donor lymphocytes in rejection is still unclear. The novel immunosuppressant, FTY720, is reported to transfer peripheral blood lymphocytes (PBLs) to lymphoid tissues such as mesenteric lymph nodes (MLNs) and Peyer patches (PP). In the present study, the number of donor lymphocytes in the graft was increased by FTY720, and the influence on rejection was studied in a rat model. Furthermore, the number of the PBL of recipient was decreased by FTY720 before SBTx and the effect on rejection was examined.

MATERIALS AND METHODS

Orthotopic total SBTx was performed in Brown-Norway and Lewis rats. In the donor pretreatment study, FTY720 was administrated to donor rats 24 h prior to harvesting to increase the number of graft lymphocytes (FTY donor-pretreated group). In contrast, MLNs were surgically removed from the grafts to decrease the number of graft lymphocytes (MLN-resected group). In the recipient pretreatment study, FTY720 was administrated to recipient rats 24 h before SBTx to decrease recipient PBL (FTY group). In contrast, a subclinical dose of cyclosporine A (CsA) was administrated after SBTx (CsA group). Rats were administrated preoperative FTY720 combined with post-SBTx CsA (FTY+CsA group). Graft survival, pathology, lymphocyte count, and subtype were examined.

RESULTS

In the donor pretreatment study, pretreatment with FTY720 did not enhance graft rejection. MLN resection did not prolong graft survival. In the recipient pretreatment study, FTY720 caused a significant reduction in the number of infiltrating lymphocytes in the graft, as well as the percentage of recipient CD4+ and CD25+ cells within the graft. FTY720 and CsA synergistically prolonged graft survival.

CONCLUSION

SBTx rejection correlated with the number of recipient PBL, and not with the number of donor lymphocytes transplanted together with the graft. The pretreatment of the recipient with FTY720 was effective in the case of combined use of the low-dose postoperative CsA.

Semiquantative analysis of expression of mucosal addressin cell adhesion molecule-1 during small bowel graft rejection in rats

AIM

Mucosal addressin cell adhesion molecule-1 (MAdCAM-1) mediates the homing of lymphocytes to gut-associated lymphoid tissues (GALT). We performed a semiquantative analysis of MAdCAM-1 expression during small bowel graft rejection.

METHODS

Orthotopic small bowel transplantations (SBT) were performed from BN rats to LEW rats. Isografted animals served as controls. Animals were sacrificed on days 3, 4, 5, 6, and 7 after SBT. Cryostat sections were prepared from grafts, including Peyer's patches (PPs). Indirect immunoperoxidase staining was performed using mAbs against MAdCAM-1. The degree of vascular endothelial staining on high endothelial venules (HEV) in the PPs was graded from 1 (low levels) to 5 (high levels), and in the vessels of the lamina propria from 1 (faint), 2 (low at the base of villi), 3 (low to the middle of villi), 4 (high to the middle of villi), to 5 (high to villus tip).

RESULTS

MAdCAM-1 expression on HEVs in PPs was down-regulated during rejection. In contrast its expression on endothelial cells of vessels in the lamina propria was up-regulated during rejection.

CONCLUSION

Alteration in MAdCAM-1 expression may be associated with the development of SB graft rejection. The vessels at the base of villi, which are associated with lymphocyte recruitment, may become sites of intense immune reactivity during the early phase of small bowel allograft rejection.

Expression of mucosal addressin cell adhesion molecule-1 (MAdCAM-1) during small-bowel graft rejection in rats

BACKGROUND

Mucosal addressin cell adhesion molecule-1 (MAdCAM-1) is a critical endothelial adhesion molecule for lymphocyte trafficking to gut-associated lymphoid tissues (GALT) under physiological conditions. It is expressed on special postcapillary venules, that is the high endothelial venules (HEV) in GALT. In this study, we investigated changes in MAdCAM-1 expression during small-bowel graft rejection.

METHODS

Orthotopic small-bowel transplantation (SBT) with portocaval drainage was performed from brown Norway (BN) rats to Lewis (LEW) rats. Isografted (LEW --> LEW) and untransplanted animals served as controls. Animals were killed on days 3, 4, 5, 6 and 7 after SBT. Cryostat sections (6 microm thick) were prepared from normal small-bowel tissues and small-bowel grafts, including Peyer patches (PPs). Indirect immunoperoxidase staining was performed using monoclonal antibodies (mAbs) against rat MAdCAM-1 (OST12).

RESULTS

In the PPs of controls, MAdCAM-1 antibodies specifically stained the endothelial cells of HEV, which were predominantly located in the interfollicular areas. In the allografts on day 4 after SBT, the MAdCAM-1 expression was weaker on the HEV in the PPs than in the controls. In the lamina propria of controls, a faint expression of MAdCAM-1 on vessels was observed. On day 4 after allogeneic SBT, the MAdCAM-1 was more strongly expressed on the endothelial cells of the vessels at the base of the villi. As rejection developed, the MAdCAM-1 expression on the vessels progressed toward the villus tip.

CONCLUSIONS

The change of MAdCAM-1 expression may be involved in the development of small-bowel graft rejection. The vessels at the base of villi, which is associated with lymphocyte recruitment, may become a site of intense immune reactivity in the early phase of small-bowel allograft rejection.

Persistent rejection of peritubular capillaries and tubules is associated with progressive interstitial fibrosis

BACKGROUND

We have reported that a 12-day course of high dose cyclosporine A treatment in thymectomized miniature swine with major histocompatibility complex (MHC) class I-mismatched renal allografts results in transient acute rejection followed by either in chronic rejection (progression group) or graft acceptance (recovery group). Here, we examined the differential features between both groups in the peritubular capillaries (PTCs) and tubules to clarify the pathogenesis of the progressive interstitial fibrosis in chronic rejection.

METHODS

Morphometric and immunohistochemical studies were performed on serial renal biopsies (days 0 to 100) obtained from both groups, focusing on the cellular infiltrate, rejection of PTCs and tubules, myofibroblast accumulation, and progressive interstitial fibrosis.

RESULTS

In the progression group, acute rejection occurred by day 8 and progressed to chronic rejection by day 100, with the development of interstitial fibrosis. PTC endothelial cell and tubular epithelial cell death associated with CD3+ cell infiltration was evident, confirmed by nick end-labeling (TUNEL), commencing by day 8 and continuing thereafter. In acute rejection, destruction of PTCs and tubules accompanied by disruption of basement membrane (BM) occurred with capillaritis or tubulitis in areas with a severe cellular infiltrate. During the development of chronic rejection, capillaritis of PTCs and tubulitis continued by day 100, accompanied by persistent T cell infiltration, and the remaining PTCs and tubules exhibited progressive atrophy with thickening and/or lamination of BM. On day 100, identifiable PTCs and tubules were lost in areas of interstitial fibrosis. Proliferating (PCNA+) alpha-actin+ myofibroblasts accumulated around PTCs, tubules and in interstitium, and widespread interstitial fibrosis developed by day 100. In contrast, in the recovery group, injured PTCs and tubules recovered by day 100 based on the resolution of acute rejection, and minimal loss of PTCs and tubules was evident by day 100 with minimal interstitial fibrosis.

CONCLUSIONS

Persistent rejection directed at PTCs and tubules, and proliferation of myofibroblasts are prominent features in the progressive interstitial fibrosis in chronic rejection, and are probably key events in its pathogenesis.

Rejection of peritubular capillaries in renal allo- and xeno-graft

The microvasculature plays an important role in the pathogenesis of humoral- and cell-mediated renal allo- and xeno-graft rejection. Peritubular capillary (PTC) endothelium expresses the major histocompatibility complex (MHC) class I and II antigens in the resting phase, as does the glomerular capillary endothelium, suggesting that these cells may be major immune targets. However, the role of PTCs in renal allo- and xeno-graft rejection is unclear. In this review, we discuss injury and subsequent remodeling of PTCs in both humoral- and cell-mediated rejection in allo- and xeno-grafts. Recent evidence suggests that PTC injury and endothelial cell death occur during both cell- and humoral-mediated rejection. Severe PTC rejection contributes to deterioration of graft function and acute graft loss. The mild but recurrent form of PTC rejection is associated with progressive interstitial fibrosis and chronic rejection. Following endothelial injury, the remaining PTC endothelium activates with up-regulation of allo-antigens and adhesion molecules, and down-regulation of anti-coagulant proteins. Subsequent to this, more severe rejection and graft dysfunction occur. Therefore, a careful analysis of cellular- and antibody-mediated rejection in PTCs is important in the diagnosis of rejection, prediction of graft prognosis, and in further development of new anti-rejection therapies.

Homing of in vitro-generated donor antigen-reactive CD4+ T lymphocytes to renal allografts is alpha 4 beta 1 but not alpha L beta 2 integrin dependent

The extravasation and sequestration of Ag-reactive T lymphocytes into vascularized organ allografts depend on a cascade of complex interactions among circulating lymphocytes, endothelial cells, and extracellular matrix proteins. Ag-activated donor-specific CD4 T cells are major initiators and effectors in the allograft rejection response. Interfering with the intragraft homing of activated CD4 T cells may represent a novel therapeutic approach in transplant recipients. We have developed a FACS-based short-term homing assay that allows tracing in vitro-generated Ag-reactive CD4 T cells after adoptive transfer in test rat recipients. Allospecific cell lines were preincubated with anti-alpha(4)beta(1) or anti-alpha(L)beta(2) mAb, because of enhanced expression of both integrin receptors after alloactivation. The pretreated Lewis(BN) lymphocytes were carboxyfluorescein diacetate succinimidyl ester labeled and adoptively transferred into Lewis rat recipients of Brown Norway kidney allografts. The injection of equal numbers of PKH-26-labeled untreated cells allowed quantitative comparison of both populations in the same animal. Ex vivo treatment with anti-alpha(4)beta(1) mAb diminished intragraft infiltration of adoptively transferred T cells by 85% in a donor-specific fashion. In contrast, treatment with anti-alpha(L)beta(2) mAb did not affect intragraft cell sequestration. Hence, blocking alpha(4)beta(1) integrin interactions represents a novel strategy in preventing local intragraft recruitment of Ag-reactive CD4 T cells in transplant recipients.

Thymus Requirement and Antigen Dependency in the “Infectious” Tolerance Pathway in Transplant Recipients

We have shown that features of infectious tolerance, as originally described in thymectomized mice, may be applied to euthymic rat recipients of heart transplants. We now report on studies aimed at exposing mechanisms underlying the infectious tolerance pathway, with emphasis on the role of thymus and alloantigen. Pretransplant thymectomy diminished the efficacy of CD4-targeted therapy, with donor-specific tolerance induced in ∼50% of recipients. Thymus was required for generation of regulatory T cells under the cover of CD4 mAb therapy and for the ability of these cells to confer infectious tolerance. However, thymus was not mandatory to maintain an infectious-permissive environment in cohorts of adoptively transferred recipients. Intragraft expression of IL-2, IL-4, and IL-10 genes was diminished in euthymic and thymectomized tolerant hosts. However, grafts in the latter group showed significant IFN-γ gene expression, suggesting a less efficient down-regulation of Th1-like cells in the absence of regulatory cells. Indeed, exogenous challenge with rIL-2 or freshly alloactivated spleen cells recreated rejection in thymectomized, but not euthymic, hosts, suggesting that a state of cytokine-responsive anergy contributes to the “noninfectious” form of tolerance in thymectomized rats. The infection-tolerant state did not result from “graft adaptation,” and regulatory T cells restricted for the original alloantigen were exposed to its continuous stimulation. The effective memory for suppression was dependent upon persistent donor-specific alloantigen stimulation; it disappeared within 3 weeks after its removal. Hence, both central and peripheral immune mechanisms, orchestrated by the tolerizing alloantigen, contribute to the infectious tolerance pathway in CD4 mAb-treated rat transplant recipients.

Blockade of very late antigen-4 integrin binding to fibronectin in allograft recipients: I. Treatment with connecting segment-1 peptides prevents acute rejection by suppressing intragraft mononuclear cell accumulation, endothelial activation, and cytokine expression

BACKGROUND

Allograft rejection is associated with infiltration of inflammatory cells and local deposition of fibronectin (FN). This study was carried out to examine the hypothesis that peptides known to specifically block adhesive interactions between the connecting segment-1 (CS1)-binding domain of FN and alpha4beta1 integrin on circulating cells may interfere with the immune cascade, which would lead to acute rejection in transplant recipients.

METHODS AND RESULTS

Cardiac allografts from Lewis x Brown Norway F1 hybrids were rejected in 7+/-1 days in Lewis rats. Treatment with bioactive CS1 peptides (4 mg/kg/day i.v. for 7 days) abrogated acute rejection and prolonged cardiac allograft survival to 13+/-1 days (P<0.001). This effect correlated with decreased expression of total fibronectin and cell adhesion molecules, such as alpha4beta1, vascular cell adhesion molecule-1, intercellular adhesion molecule-1, as well as reduced infiltration by CD4+ and CD8+ T cells at the graft site. Treatment with CS1 peptides decreased alloantigen activation, as evidenced by decreased intragraft infiltration by CD25+ cells, and diminished expression of mRNA coding for Th1 (interleukin [IL]-2, interferon-gamma)- and Th2 (IL-4, IL-5, IL-6)-type cytokines. CS1-mediated immunosuppressive effects could be reversed and acute rejection recreated after adjunctive treatment of rats with recombinant IL-2.

CONCLUSION

Our data are consistent with the model in which in vivo interaction between the alpha4beta1 integrin receptor and the cell-associated CS1 motif of FN is critical for rejection cascade. The novel therapeutic approach of selectively blocking the alpha4beta1-FN activation pathway with CS1 peptides prevents acute allograft rejection by inhibiting expansion of antigen-specific T cells and inducing a transient state of cytokine-responsive anergy in the residual T-cell population.

Reduction in peripheral nerve allograft antigenicity with warm and cold temperature preservation

Lymphocyte migration into fresh and preserved peripheral nerve allografts was assessed to determine the effects of preservation time, preservation temperature, and graft harvest technique on the immunologic response to the peripheral nerve allograft. Peroneal nerve was harvested from either live or cadaveric (tissue) donors and stored as 1.5-cm segments at 5 degrees C or 37 degrees C for 1, 3, 5, or 7 days. Each of nine outbred ewes then received multiple segments of peroneal autograft, fresh allograft, and preserved nerve allograft implants. Lymphocyte migration was studied 7 days after implantation by intravenous injection of autologous 111In-labeled lymphocytes and quantified by gamma counter. Lymphocyte migration into fresh allografts (7212 +/- 1575) increased an average of 4.1 times over fresh autograft tissue (1758 +/- 421; p < 0.05). Short-term preservation (24 hours) at both temperatures enhanced lymphocyte migration into pretreated allograft tissue (12684 +/- 2575 at 5 degrees C, 8751 +/- 1577 at 37 degrees C) as compared with fresh allograft (7212 +/- 1575). Conversely, 7 days of pretreatment at both 5 degrees C (3586 +/- 1421) and 37 degrees C (1570 +/- 414) resulted in migration values not significantly different from autograft. No statistically significant difference was seen between grafts harvested from live (5710 +/- 1651) versus cadaveric (tissue) donors (4013 +/- 832) after 5 days of cold preservation.

Effects of desferrioxamine on human cytomegalovirus replication and expression of HLA antigens and adhesion molecules in human vascular endothelial cells

Desferrioxamine (DFO), commonly used in therapy as a chelator of ferric ion in disorders of iron overload, is a potent inhibitor of human cytomegalovirus (HCMV) replication in cultured fibroblast cells. Moreover, DFO has immunomodulatory activity both in vitro and in vivo. We studied DFO effects on HCMV replication in cultured human endothelial cells and on the expression of several cell surface molecules, which mediate interactions of endothelial cells with other cell types in the immune system. The concentrations of DFO required for 50% reduction in the number of endothelial cells expressing HCMV late antigen, ranged for several HCMV strains from 5.2 to 8.8 microM. DFO concentrations ranging from 5 to 40 microM inhibited cellular DNA synthesis in a dose-dependent manner without any significant effects on the cell viability. DFO at 10 microM concentration suppressed expression of intercellular adhesion molecule-1 (ICAM-1) and endothelial leucocyte adhesion molecule-1 (ELAM-1), while it had no significant effect on the expression of vascular cell adhesion molecule-1 (VCAM-1). Expression of HLA class I and class II was not influenced by DFO treatment. The results showed that DFO is both effective in inhibition of HCMV replication and expression of ICAM-1 and ELAM-1 in endothelial cells, a combination that warrants attention to its potential use to prevent HCMV-induced allograft rejection in transplant recipients.

Adhesion molecules and transplantation

OBJECTIVE

Accessory adhesion molecules are thought to influence the first interaction between host leukocytes and graft vascular endothelial cells. Their role in transplantation is reviewed.

SUMMARY

Adhesion molecules have been divided into three major families: the selectins, the integrins, and the immunoglobulin superfamily. Selectins are small proteins that mediate the first contact between stimulated endothelial cells and leukocytes. Integrins interact with cytoskeletal components of cells, presumably coordinating extracellular stimuli with cytoskeleton dependent actions, such as motility, shape change, and phagocytic responses. Members of the immunoglobulin superfamily are structurally homologous, although they do not necessarily share similar functions. They are involved in T-cell proliferation and intracellular events.

METHODS

Various groups of investigators have studied the influence and expression of adhesion molecules following transplantation. The authors of this article have reviewed and summarized the available literature.

RESULTS

Many different adhesion molecules are up-regulated during the rejection event. Treatment of transplant recipients with monoclonal antibodies against accessory molecules, such as leukocyte function associated antigen 1 (LFA-1) and intercellular adhesion molecule 1 (ICAM-1), has resulted in either a prolongation of transplant survival or the induction of tolerance in some models. Other interventions are under study.

CONCLUSION

By mediating the initial leukocyte/endothelial cell interactions, adhesion molecules may play an important role in graft rejection, mediation of infiltration into the graft, and dissemination of the antigenic message to the lymphoid tissues of the host. Future studies will have to deal not only with conceptualizing their function and mechanisms of action, but also with manipulating their interrelationships to the benefit of the graft recipient.

The biology of acute transplant rejection

An intriguing and increasingly understood facet of immune responses is the ability of a recipient to destroy a foreign tissue or organ graft. The phenomenon of acute rejection of an allograft involves a series of complex and inter-related cellular and humoral events, culminating in graft death. Some of the current thinking surrounding this phenomenon is reviewed.

Lymphocyte homing

The phenomenon of "homing" is discussed with respect to patterns of lymphocyte circulation and the molecules on the surface of both endothelium and lymphocytes that mediate this process. In addition, the data are analysed in the context of a model for lymphocyte homing.