Involvement of antibody-dependent apoptosis in graft rejection

Conductance Artery Wall Layers and Their Respective Roles in the Clearance Functions

Evolutionary organization of the arterial wall into layers occurred concomitantly with the emergence of a highly muscularized, pressurized arterial system that facilitates outward hydraulic conductance and mass transport of soluble substances across the arterial wall. Although colliding circulating cells disperse potential energy within the arterial wall, the different layers counteract this effect: (1) the endothelium ensures a partial barrier function; (2) the media comprises smooth muscle cells capable of endocytosis/phagocytosis; (3) the outer adventitia and perivascular adipocytic tissue are the final receptacles of convected substances. While the endothelium forms a physical and a biochemical barrier, the medial layer is avascular, relying on the specific permeability properties of the endothelium for metabolic support. Different components of the media interact with convected molecules: medial smooth muscle cells take up numerous molecules via scavenger receptors and are capable of phagocytosis of macro/micro particles. The outer layers-the highly microvascularized innervated adventitia and perivascular adipose tissue-are also involved in the clearance functions of the media: the adventitia is the seat of immune response development, inward angiogenesis, macromolecular lymphatic drainage, and neuronal stimulation. Consequently, the clearance functions of the arterial wall are physiologically essential, but also may favor the development of arterial wall pathologies. This review describes how the walls of large conductance arteries have acquired physiological clearance functions, how this is determined by the attributes of the endothelial barrier, governed by endocytic and phagocytic capacities of smooth muscle cells, impacting adventitial functions, and the role of these clearance functions in arterial wall diseases.

Phylogenic Determinants of Cardiovascular Frailty, Focus on Hemodynamics and Arterial Smooth Muscle Cells

The evolution of the circulatory system from invertebrates to mammals has involved the passage from an open system to a closed in-parallel system via a closed in-series system, accompanying the increasing complexity and efficiency of life’s biological functions. The archaic heart enables pulsatile motion waves of hemolymph in invertebrates, and the in-series circulation in fish occurs with only an endothelium, whereas mural smooth muscle cells appear later. The present review focuses on evolution of the circulatory system. In particular, we address how and why this evolution took place from a closed, flowing, longitudinal conductance at low pressure to a flowing, highly pressurized and bifurcating arterial compartment. However, although arterial pressure was the latest acquired hemodynamic variable, the general teleonomy of the evolution of species is the differentiation of individual organ function, supported by specific fueling allowing and favoring partial metabolic autonomy. This was achieved via the establishment of an active contractile tone in resistance arteries, which permitted the regulation of blood supply to specific organ activities via its localized function-dependent inhibition (active vasodilation). The global resistance to viscous blood flow is the peripheral increase in frictional forces caused by the tonic change in arterial and arteriolar radius, which backscatter as systemic arterial blood pressure. Consequently, the arterial pressure gradient from circulating blood to the adventitial interstitium generates the unidirectional outward radial advective conductance of plasma solutes across the wall of conductance arteries. This hemodynamic evolution was accompanied by important changes in arterial wall structure, supported by smooth muscle cell functional plasticity, including contractility, matrix synthesis and proliferation, endocytosis and phagocytosis, etc. These adaptive phenotypic shifts are due to epigenetic regulation, mainly related to mechanotransduction. These paradigms actively participate in cardio-arterial pathologies such as atheroma, valve disease, heart failure, aneurysms, hypertension, and physiological aging.

Association of Local Intrapulmonary Production of Antibodies Specific to Donor Major Histocompatibility Complex Class I With the Progression of Chronic Rejection of Lung Allografts

BACKGROUND

Antibody-mediated rejection may lead to chronic lung allograft dysfunction, but antibody-mediated rejection may develop in the absence of detectable donor-specific antibody (DSA) in recipient serum. This study investigated whether humoral immune responses develop not only systemically but locally within rejected lung allografts, resulting in local production of DSA.

METHODS

Lewis rats received orthotopic left lung transplantation from Lewis (syngeneic control) or Brown-Norway (major histocompatibility complex-mismatched allogeneic) donor rats. Rats that underwent allogeneic lung transplantation were subsequently administered cyclosporine until day 14 (short immunosuppression) or day 35 (long immunosuppression). The lung grafts and spleens of recipient animals were tissue cultured for 4 days, and the titer of antibody against donor major histocompatibility complex molecules was assayed by flow cytometry. Explanted lung grafts were also evaluated pathologically.

RESULTS

By day 98, DSA titers in supernatants of lung graft (P = 0.0074) and spleen (P = 0.0167) cultures, but not serum, from the short immunosuppression group were significantly higher than titers in syngeneic controls. Cultures and sera from the long immunosuppression group showed no production of DSA. Microscopically, the lung grafts from the short immunosuppression group showed severe bronchiole obliteration and parenchymal fibrosis, along with lymphoid aggregates containing T and B cells, accompanying plasma cells. These findings suggestive of local humoral immune response were not observed by days 28 and 63.

CONCLUSIONS

DSA can be locally produced in chronically rejected lung allografts, along with intragraft immunocompetent cells. Clinical testing of DSA in serum samples alone may underestimate lung allograft dysfunction.

Autologous adipose-derived mesenchymal stem cells improve healing of coiled experimental saccular aneurysms: an angiographic and histopathological study

PURPOSE

Long-term occlusion of coiled aneurysms frequently fails, probably because of poor intrasaccular healing and inadequate endothelialization across the aneurysm neck. The purpose of this study was to determine if attachment of autologous mesenchymal stem cells (MSCs) to platinum coils would improve the healing response in an elastase-induced aneurysm model in rabbits.

MATERIALS AND METHODS

With approval from the institutional animal care and use committee, aneurysms were created in rabbits and embolized with control platinum coils (Axium; Medtronic) (n=6) or coils seeded ex vivo with autologous adipose-tissue MSCs (n=7). Aneurysmal occlusion after embolization was evaluated at 1 month with angiography. Histological samples were analyzed by gross imaging and graded on the basis of neck and dome healing on H&E staining. Fibrosis was evaluated using a ratio of the total area presenting collagen. Endothelialization of the neck was quantitatively analyzed using CD31 immunohistochemistry. χ² and Student's t-test were used to compare groups.

RESULTS

Healing score (11.5 vs 8.0, p=0.019), fibrosis ratio (10.3 vs 0.13, p=0.006) and endothelialization (902 262 μm² vs 31 810 μm², p=0.041) were significantly greater in the MSC group. The MSC group showed marked cellular proliferation and thrombus organization, with a continuous membrane bridging the neck of the aneurysm. Angiographic stable or progressive occlusion rate was significantly lower in the MSC group (0.00, 95% CI 0.00 to 0.41) compared with controls (0.67, 95% CI 0.22 to 0.96) (p=0.02).

CONCLUSIONS

Autologous MSCs attached to platinum coils significantly improve histological healing, as they result in improved neck endothelialization and collagen matrix formation within the aneurysm sac.

Antibody-mediated rejection of arterialised venous allografts is inhibited by immunosuppression in rats

Objectives and Design

We determined in a rat model (1) the presence and dynamics of alloantibodies recognizing MHC complexes on quiescent Brown-Norway (BN) splenic cells in the sera of Lewis (LEW) recipients of Brown-Norway iliolumbar vein grafts under tacrolimus immunosuppression; and (2) the presence of immunoglobulins in the wall of acute rejected vein allografts.

Materials and Methods

Flow cytometry was used for the analysis of day 0, 14 and 30 sera obtained from Lewis recipients of isogeneic iliolumbar vein grafts (group A) or Brown-Norway grafts (group B, C) for the presence of donor specific anti-MHC class I and II antibodies. Tacrolimus 0.2 mg/kg daily was administered from day 1 to day 30 (group C). Histology was performed on day 30.

Results

Sera obtained preoperatively and on day 30 were compared in all groups. The statistically significant decrease of anti MHC class I and II antibody binding was observed only in allogenic non-immunosuppressed group B (splenocytes: MHC class I - day 0 (93%±7% ) vs day 30 (66%±7%), p = 0.02, MHC class II - day 0 (105%±3% ) vs day 30 (83%±5%), p = 0.003; B-cells: MHC class I - day 0 (83%±5%) vs day 30 (55%±6%), p = 0.003, MHC class II - day 0 (101%±1%) vs day 30 (79%±6%), p = 0.006; T-cells: MHC class I - day 0 (71%±7%) vs day 30 (49%±5%), p = 0.04). No free clusters of immunoglobulin G deposition were detected in any experimental group.

Conclusion

Arterialized venous allografts induce strong donor-specific anti-MHC class I and anti-MHC class II antibody production with subsequent immune-mediated destruction of these allografts with no evidence of immunoglobulin G deposition. Low-dose tacrolimus suppress the donor-specific antibody production.

Autologous mesenchymal stem cell endografting in experimental cerebrovascular aneurysms

INTRODUCTION

Coiling is the gold standard for the treatment of intracranial aneurysms. However, some issues associated with endovascular treatment limit its long-term efficiency. Recanalization with coil compaction is certainly the most important. New approaches may be considered to promote thrombus colonization by mesenchymal cells and aneurysm healing. In the present study, we have percutaneously delivered autologous bone marrow mesenchymal stem cells (BMSCs) to an elastase-induced rabbit carotid aneurysm model in vivo.

METHODS

Autologous mesenchymatous stem cells were obtained after femoral puncture and bone marrow aspiration. After 2 weeks of in vitro cell culture, five million BMSCs were grafted in the carotid aneurysm using an endovascular approach.

RESULTS

We demonstrated the feasibility of in vivo percutaneous seeding of autologous BMSCs in the aneurysm by positive Hoechst fluorostaining. Two weeks later, conventional angiography showed an increase in median aneurysmal surface in the sham group, whereas this surface was decreased in the group treated with BMSCs, +28.4 versus -26.4 %, respectively (p = 0.01). BMSC seeding resulted in intimal hyperplasia with cell colonization and disappearance of the thrombus.

CONCLUSION

In conclusion, percutaneous seeding of BMSCs may colonize and heal the arterial wall thus limiting aneurysm expansion.

Picking transplant glomerulopathy out of the CAN: evidence from a clinico-pathological evaluation

Background

Since the term chronic allograft nephropathy (CAN) was removed from the Banff scheme in 2005, transplant glomerulopathy (TG) has been regarded as a clinicopathological entity that is one of the major causes of graft loss. To assess the distinction between CAN and TG, we performed a comprehensive evaluation comparing TG with traditional CAN.

Methods

We compared the clinicopathological features of 43 cases of TG with 43 matched cases of non-TG CAN (non-TG group) after renal transplantation. TG was diagnosed by light microscopy based on the double contours of the glomerular basement membranes, and the Banff 97 classification system was used to score TG severity (cg0-3).

Results

Compared to the control group, we found a significantly higher incidence of positivity for human leukocyte antigen class-I and II antibodies, a higher incidence of hepatitis C virus (HCV) infection, and poorer graft survival in TG patients. Clinically, TG was associated with a higher prevalence of proteinuria, hematuria, anaemia and hypoalbuminemia. Histologically, TG strongly correlated with antibody related microcirculatory injuries, including glomerulitis, peritubular capillaritis and peritubular capillary (PTC) C4d deposition. Interestingly, the TG patients showed a significantly higher incidence of IgA deposition than the control patients. C4d-positive TG was correlated with higher TG and PTC scores, and PTC C4d deposition was correlated with a more rapid progression to graft dysfunction. TG accompanied by HCV infection was associated with heavier proteinuria, higher TG and C4d scores, and poorer graft survival.

Conclusions

TG presents clinicopathological features that are distinct from non-TG cases and leads to poorer outcomes. PTC C4d deposition is related to a more rapid progression to graft loss, suggesting ongoing antibody reactivity. HCV-positive TG is a more severe sub-entity, that requires further investigation.

Contribution of B cells and antibody to cardiac allograft vasculopathy

BACKGROUND

The aim of this study was to determine the role of alloantibody in the development of cardiac allograft vasculopathy (AV). AV is the main pathologic indicator of chronic cardiac graft rejection resulting in graft loss at 10 years posttransplant. In AV, a neointimal lesion forms resulting in luminal occlusion and damage to the transplanted organ. AV is T-cell mediated, but the role played by B cells and antibody in AV development has been controversial. No studies have been conducted in the presence of a clinically relevant immunosuppressant. In our study, we use cyclosporin A, a calcineurin inhibitor.

METHODS

Two models of B-cell deficiency were used as recipients of a C3H/HeJ abdominal aortic graft; grafts were harvested at 8 weeks. T- and B-cell immunodeficient mice (RAG1-/-) received passively transferred anti-C3H antibody, raised in B6 mice. Cyclosporin A was administered daily to both control and experimental groups. Alpha-actin staining was used to identify myofibroblasts in the neointima.

RESULTS

Lesions in B-cell-deficient B6 mice were not significantly different in size from those of control mice. Lesions in both B-cell-deficient and wild-type mice showed similar levels of alpha-actin positivity. Passive transfer of antibody to RAG1-/- mice resulted in small, alpha-actin-positive lesions.

CONCLUSIONS

B cells are not required for the development of AV, but the presence of an alloantibody can contribute to AV. We hypothesize that the alloantibody mediates AV by initiating complement-mediated killing of smooth muscle cells, based on an in vitro work. Of interest, we found that the neointimal lesions of B-cell-deficient mice and mice that received antibody showed the presence of alpha-actin in myofibroblasts.

Anti-human leukocyte antigen and donor-specific antibodies detected by luminex posttransplant serve as biomarkers for chronic rejection of renal allografts

BACKGROUND

Although the incidence of early acute rejection could have been diminished in the past, the long-term renal allograft survival could not benefit from the introduction of more effective immunosuppressive regimens mainly aiming at cellular rejection mechanisms. The cause of chronic rejection is still discussed controversially. Here, we demonstrate to what extent human leukocyte antigen (HLA) antibodies (HLAab) posttransplant contribute to late graft outcome.

METHODS

A total of 1014 deceased kidney transplant recipients transplanted at the Charité hospital were monitored in a cross-sectional manner for the development of HLAab using Luminex Single Antigen beads. Patients with stable kidney function at a median of 5-years posttransplant were tested once for HLAab and monitored for 5.5 years after testing.

RESULTS

Thirty percent of recipients showed HLAab. Donor-specific antibodies (DSA) were found in 31% of antibody positive patients. The presence of DSA was associated with a significantly lower graft survival of 49% vs. 83% in the HLAab negative group (P< or =0.0001). Non-DSAs also had an adverse effect on graft survival (70% vs. 83%; P=0.0001). In a prospective analysis of 195 patients with repeatedly no detectable HLAab, the survival probability was 94% as opposed to 79% survival among patients who developed HLAab de novo after the first testing (P=0.05).

CONCLUSIONS

We confirmed that HLAab produced even late after transplantation are detrimental to graft outcome. DSA were proven to have a strong adverse impact on graft survival. The results indicate that a posttransplant HLAab monitoring routine could be appropriate to improve long-term results.

Transplant glomerulopathy: clinical and pathological correlations

OBJECTIVE

Chronic transplant glomerulopathy (TG) is one of the leading causes of severe posttransplantation proteinuria and graft loss. Our current knowledge about risk factors for the development of TG, as well as factors that affect its dynamics and prognosis, is poor. We sought to describe the pathological and clinical risk factors and correlations of TG as well as parameters that influenced the survival of grafts with that pathology.

MATERIALS AND METHODS

We retrospectively reevaluated 86 kidney transplant cases with TG that have been recognized on the basis of an indication biopsy since 1997. All TG as well as all pre-TG (previous) biopsies were characterized for the presence of C4d deposits in the graft.

RESULTS

Younger recipient age and minimal immunosuppression due to drug withdrawal or suboptimal drug doses/blood levels within 3 to 6 months preceding the biopsy were associated with C4d deposition in peritubular capillaries (PTC; P = .0053 and P = .0365, respectively). Diffuse PTC-itis (P = .029, RR [95% confidence interval] = 3.349 [1.131-9.919]) and total interstitial inflammation score (P = .015, RR [95% confidence interval] = 9.662 [1.784-52.329]) were observed to show a negative impact on graft survival. C4d deposition in PTC and glomeruli, the level of pretransplantation sensitization, episodes of acute rejection, and C4d in previous (pre-TG) biopsies did not influence the survival of grafts with TG.

CONCLUSIONS

Younger recipient age and minimal immunosuppression were associated with C4d positivity in grafts with TG. The survival of kidney grafts with TG was significantly affected by the magnitude of inflammation in the interstitium and PTC, but not by C4d positivity in PTC and glomeruli.

Transplant glomerulopathy: subclinical incidence and association with alloantibody

Transplant glomerulopathy (TG) usually has been described as part of a constellation of late chronic histologic abnormalities associated with proteinuria and declining function. The current study used both protocol and clinically-indicated biopsies to investigate clinical and subclinical TG, their prognosis and possible association with alloantibody. We retrospectively studied 582 renal transplants with a negative pre-transplant T-cell complement dependent cytotoxicity crossmatch. TG was diagnosed in 55 patients, 27 (49%) based on protocol biopsy in well-functioning grafts. The cumulative incidence of TG increased over time to 20% at 5 years. The prognosis of subclinical TG was equally as poor as TG diagnosed with graft dysfunction, with progressive worsening of histopathologic changes and function. Although TG was associated with both acute and chronic histologic abnormalities, 14.5% of TG biopsies showed no interstitial fibrosis or tubular atrophy, while 58% (7/12) of biopsies with severe TG showed only minimal abnormalities. TG was associated with acute rejection, pretransplant hepatitis C antibody positivity and anti-HLA antibodies (especially anti-Class II), with the risk increasing if the antibodies were donor specific. We suggest that subclinical TG is an under-recognized cause of antibody-mediated, chronic renal allograft injury which may be mechanistically distinct from other causes of nephropathy.

Topological determinants and consequences of adventitial responses to arterial wall injury

Arteries are composed of 3 concentric tissue layers which exhibit different structures and properties. Because arterial injury is generally initiated at the interface with circulating blood, most studies performed to unravel the mechanisms involved in injury-induced arterial responses have focused on the innermost layer (intima) rather than on the outermost adventitial layer. In the present review, we focus on the involvement of the adventitia in response to various types of arterial injury leading to vascular remodeling. Physiologically, soluble vascular mediators are centrifugally conveyed by mass transport toward the adventitia. Moreover, in pathological conditions, neomediators and antigens can be generated within the arterial wall, whose outward conveyance triggers different patterns of local adventitial response. Adventitial angiogenesis, immunoinflammation, and fibrosis sequentially interact and their net balance defines the participation of the adventitial response in arterial pathology. In the present review we discuss 4 pathological entities in which the adventitial response to arterial wall injury participates in arterial wall remodeling. Hence, the adventitial adaptive immune response predominates in chronic rejection. Inflammatory phagocytic cell recruitment and initiation of a shift from innate to adaptive immunity characterize the adventitial response to products of proteolysis in abdominal aortic aneurysm. Adventitial sprouting of neovessels, leading to intraplaque hemorrhages, predominates in atherothrombosis. Adventitial fibrosis characterizes the response to mechanical stress and is responsible for the constrictive remodeling of arterial segments and initiating interstitial fibrosis in perivascular tissues. These adventitial events, therefore, have an impact not only on the vessel wall biology but also on the surrounding tissue.

Antidonor humoral transfer induces transplant arteriosclerosis in aortic and cardiac graft models in rats

OBJECTIVE

The humoral pathway is suggested as playing a key role in transplant arteriosclerosis. The humoral immunity is demonstrated in the present study to induce direct vascular lesion.

METHODS

Ten abdominal aortic grafts were performed on 4 groups of rats: Brown Norway (BN) isografts, BN to Lewis (LEW) allografts, and two BN to nude (RNU) grafted groups with and without any humoral transfer. The humoral sera were obtained by skin grafts performed in BN to LEW combination. Lewis anti-BN alloantisera was transferred in nude recipients through intraperitoneal injections. The aortic wall was histologically studied with morphometric analysis on the 21st day. Two additional BN to RNU aortic graft groups were evaluated by immunohistochemistry on days 3 (10 rats) and 10 (10 rats).

RESULTS

In the absence of the humoral transfer, the BN aortic wall implanted in RNU remained intact. The humoral transfer induced a marked intimal proliferation (63 +/- 4 vs 4 +/- 1.1 microm; P < .001) and an adventitial cell infiltration (5.1 +/- 0.7 vs 2.8 +/- 0.6 x 10(3) c/mm2, P < .001). The medial thickness and the medial cell density were not modified. On day 3, the remaining endothelial cells were covered by immunoglobulin G deposits. On day 10 the endothelial cells disappeared completely and intimal proliferation occurred. In an additional cardiac graft group, transplant coronary arteriopathy was evidenced in 7 of the 9 nude recipients that had undergone the humoral transfer.

CONCLUSION

The transplant arterial occlusive lesion is demonstrated here (1) to be induced by humoral antidonor immunity and (2) to be linked to an adventitial or perivascular inflammation.

Peritubular capillary damage in acute humoral rejection: an ultrastructural study on human renal allografts

The ultrastructural features of peritubular capillary (PC) damage was studied in 12 kidney allografts with acute humoral rejection (AHR). AHR manifested in diffuse linear PC staining for C4d, and histology consistent with Banff grade III in 7 recipients and Banff grade II in 5. Allografts with acute tubular necrosis served as controls. First biopsies (post-transplantation day 16.2 +/- 2.2): The intra-capillary exudate comprised monocytes (59%), polymorphonuclears (14%), lymphocytes (12%) and not otherwise specified mononuclears (15%). Three patterns of focal PC endothelial injury were observed: lysis, an increased rate of apoptosis and fragmentation. No correlation was found between the respective damage types and the inflammatory cell types or the Banff grades. Controls revealed endothelial swelling, detachment from basement membrane and fragmentation. Follow-up biopsies: Monocytes transformed into macrophages intra-luminally. The reparative changes comprised endothelial cytoplasmic protrusions, binucleated endothelial cells and capillary sprouts. Early transplant capillaropathy and transplant glomerulopathy were noted in 2 recipients. Literature data indicate that lysis is mediated by anti-HLA alloantibodies; apoptosis, demonstrated first in the present study, may be induced by non-HLA-type anti-endothelial antibodies. Fragmentation is caused by ischemia. Ongoing endothelial injury leads to transplant capillaropathy and transplant glomerulopathy, the characteristic lesions of chronic rejection.

Lymphoid neogenesis in chronic rejection: evidence for a local humoral alloimmune response

Recent advances indicate that, in various chronic inflammatory disorders, the activation of the immune system is triggered locally rather than in lymphoid organs. In this study, we have evaluated whether the humoral alloimmune response involved in chronic rejection is elicited within the graft. We used the rat aortic interposition model and microdissected the adventitia of the graft. Over time, the T cell infiltrate shifted toward a B helper phenotype. B lymphocyte clusters were detected and were the site of intense proliferation and apoptosis. Simultaneously, adventitial vascular endothelium acquired a high endothelial venule phenotype. Similar features were evidenced in the interstitium of chronically allografts (hearts and kidneys). Strikingly, ganocultured graft interstitial tissue was found to be the site of production of antibodies directed against donor MHC-I molecules. These findings, therefore, document the appearance of germinal centers in chronically rejected tissues. This lymphoid neogenesis implies that the graft is not only the target of the alloimmune response but also a site where this response actually develops, so as to optimize the communication between the targeted tissue and the immune effectors.

Induction of obliterative airway disease by anti-HLA class I antibodies

Anti-HLA class I Abs are associated with the development of bronchiolitis obliterans syndrome (BOS) after lung transplantation. BOS is characterized histologically by fibrosis and airway epithelial cell apoptosis. We have previously shown that anti-HLA class I Abs induce proliferation, growth factor production and apoptosis in airway epithelial cells in vitro. Thus, this study was designed to determine whether anti-HLA class I Abs alone could induce obliterative airway disease (OAD) in heterotopic murine tracheal allografts. Toward this, HLA-A*0201-transgenic tracheal allografts were transplanted into Rag1-deficient mice treated with the W6/32 anti-HLA class I mAb. Allografts were harvested at days +30, +45, +60 and +90. Allografts displayed epithelial metaplasia by day +45, epithelial destruction and mild cellular infiltration by day +60 and complete lumen obliteration and moderate cellular infiltration by day +90. Anti-HLA class I Abs induced the production of several growth factors and growth factor receptors and apoptosis of parenchymal cells in the allograft. In addition, anti-HLA class I Abs induced macrophages and granulocytes infiltration. The results from this study demonstrate that anti-HLA class I Abs play an important role in the pathogenesis of OAD by inducing growth factor production, apoptosis and chemotaxis of inflammatory cells.

Immune mechanisms in the pathogenesis of bronchiolitis obliterans syndrome after lung transplantation

Lung transplantation is recognized as the only viable treatment option in a variety of end-stage pulmonary diseases. However, the long-term survival after lung transplantation is limited by the development of obliterative bronchiolitis, and its clinical correlate bronchiolitis obliterans syndrome (BOS), which is considered to represent chronic lung allograft rejection. Histopathologically, BOS is an inflammatory process that leads to fibrous scarring of the terminal and respiratory bronchioles and subsequent total occlusion of the airways. The specific etiology and pathogenesis of BOS are not well understood. The current premise is that BOS represents a common lesion in which different inflammatory insults such as ischemia-reperfusion, rejection, and infection can lead to a similar histological and clinical outcome. However, the low incidence of BOS in non-transplanted individuals and the observation that early development of BOS is predicted by the frequency and severity of acute rejection episodes indicate that alloimmune-dependent mechanisms play a crucial role in the pathogenesis of BOS. The evidence presented in this review indicates that BOS is the result of humoral and cellular immune responses developed against major histocompatibility complex molecules expressed by airway epithelial cells of the lung allograft. This process is aggravated by alloimmune-independent mechanisms such as ischemia-reperfusion and infection. Currently, treatment of BOS is frequently unsuccessful. Therefore, a better understanding of the immunopathogenesis of BOS is of paramount importance toward improving long-term patient and graft survival after lung transplantation.

Seeding of Recipient Bone Marrow Cells Reduces Neointimal Hyperplasia of De-endothelialized Rat Aortic Allograft

Transplant vasculopathy is a leading cause of graft failure and a major contributor to the lack of success with small caliber vascular allografts. In this study we evaluate techniques of bone marrow cell seeding on small caliber vessels and assess the impact of this tactic on neointimal hyperplasia in de-endothelialized rat aortic allografts. In a preliminary study, bone marrow cells from Lewis rats were seeded onto the chemically de-endothelialized luminal surface of the abdominal aorta of WKY rats - with or without fibrin glue. In the allograft transplantation model, de-endothelialized fresh aortic allografts of WKY rats were orthotopically transplanted into Lewis recipients either directly (n = 6) or after recipient bone marrow cell seeding (n = 6). Histological evaluation was performed at 28 days. Bone marrow cells were able to adhere to the de-endothelialized aortic wall owing to the use of fibrin glue, but were unable to do so without fibrin glue. In the de-endothelialized allograft transplantation model, recipient bone marrow seeding led to a significant reduction of the ratio of intimal to medial area (0.40 +/- 0.08 versus 0.79 +/- 0.08, P = 0.0077). Some of the seeded cells remained in the intima for 4 weeks and some infiltrated the media, expressing CD31 or alpha-SMA. The results suggest that recipient bone marrow cell seeding on de-endothelialized aortic allograft is feasible with the use of fibrin glue and that this technique reduces neointimal hyperplasia of the graft.

T-cell flow-cytometry crossmatch and long-term renal graft survival

Flow cytometry crossmatch (FCXM) is a more sensitive technique than classical complement-dependent cytotoxicity (CDC) for the detection of donor-directed antibody before renal transplantation. Nevertheless, the role of FCXM in predicting long-term survival of kidney grafts is still unclear. The purpose of our study was to evaluate the impact of a positive T-cell FCXM (T-FCXM) on long-term kidney allografts outcome. Of the 184 consecutive kidney transplantations performed in our center between 1 January1991 and 15 November 1996 a FCXM, performed concurrently to the pre-transplant CDCXM, was available for 170 patients. The CDCXM was negative in all recipients. Among these recipients, 12 (7.1%) had a positive T-FCXM. These patients were not different from patients with a negative T-FCXM for donor and recipient age, sex, frequency of second transplantation, number of human leukocyte antigen matches or mismatches. Frequency of immunized patients was higher in kidney recipients with a positive FCXM (58.3% vs. 24.7%; p=0.02, chi-square test). Survival analysis revealed that kidney graft outcome was better in negative T-FCXM recipients (p=0.03), while patient survival was not statistically different. Our results suggest that a positive pre-transplant T-FCXM despite a negative CDCXM is associated with an impaired long-term graft survival in renal allotransplantation.

Effector mechanisms in transplant rejection

Antigens, provided by the allograft, trigger the activation and proliferation of allospecific T cells. As a consequence of this response, effector elements are generated that mediate graft injury and are responsible for the clinical manifestations of allograft rejection. Donor-specific CD8+ cytotoxic T lymphocytes play a major role in this process. Likewise, CD4+ T cells mediate delayed-type hypersensitivity responses via the production of soluble mediators that function to further activate and guide immune cells to the site of injury. In addition, these mediators may directly alter graft function by modulating vascular tone and permeability or by promoting platelet aggregation. Allospecific CD4+ T cells also promote B-cell maturation and differentiation into antibody-secreting plasma cells via CD40-CD40 ligand interactions. Alloantibodies that are produced by these B cells exert most of their detrimental effects on the graft by activating the complement cascade. Alternatively, antibodies can bind Fc receptors on natural killer cells or macrophages and cause target cell lysis via antibody-dependent cell-mediated cytotoxicity. In this review, we discuss these major effector pathways, focusing on their role in the pathogenesis of allograft rejection.

Oral graft-versus-host disease and programmed cell death: pathogenetic and clinical correlates

Graft-versus-host disease (GVHD) is an untoward complication of bone marrow transplantation. It is characterized by an immune-mediated attack by donor immune cells against various host cells and tissues, a process which may be associated with significant morbidity in affected patients. Oral lesions are a common sequelae and can serve as a highly predictive index to the presence of systemic GVHD. The oral lesions of GVHD are clinically and histologically lichenoid in nature and can be a challenge in terms of management. Ulcerated and painful mucosal lesions may represent a significant impediment to normal eating habits and nutritional intake, necessitating appropriate diagnosis and treatment. Importantly, recent evidence has indicated that programmed cell death, or apoptosis, is the major constituent in the pathogenesis of GVHD. Apoptosis not only plays a major role in normal growth and ontogeny, but has been shown to contribute to a wide spectrum of both inflammatory and neoplastic disorders. Since knowledge of apoptotic molecular pathways is requisite for understanding GVHD, the purpose of this paper is to provide a fundamental overview of the predominant apoptotic mechanisms implicated in the pathogenesis of GVHD and to relate these findings to the oral complications of the disease. Finally, we will discuss management strategies for diagnosing and treating the oral lesions of GVHD. By explicating the molecular events in the apoptotic pathway, unique therapeutic and pharmacologic strategies for regulating apoptosis may be developed in the future, reducing the morbidity associated with conditions like GVHD.

Balanced expression of mitochondrial apoptosis regulatory proteins correlates with long-term survival of cardiac allografts

Abnormal regulation of apoptosis is observed in ischemic injury and may contribute to the pathogenesis of atherosclerosis. However, its role in cardiac allograft vasculopathy (CAV), the fundamental lesion of chronic rejection (CR) in heart transplantation, remains uncertain. To clarify this issue, apoptosis was quantitated in myocardium and coronary arteries from 5 cardiac allograft donors (NL) and explanted hearts of 24 patients with ischemic cardiomyopathy (IsCM) and 15 patients with CR. Tissue samples were analyzed via end-labeling fragmented DNA [via deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)] and immunoblotting for activated caspase-3 and -9. Myocyte apoptosis assessed by TUNEL was similarly increased over NL (0.21%) in both the CR (0.88%; P < 0.01) and IsCM (0.88%; P < 0.01) groups. Activated caspase-9 levels were significantly higher in CR (14.7%) compared with IsCM (6.9%; P < 0.01) and NL (0%) groups, whereas activated caspase-3 levels were similarly elevated in both CR and IsCM (7.8 and 6.5% vs. 0% in NL; P < 0.01 and P < 0.05) groups. Expression of myocardial Bcl-2 and Bax was increased in CR compared with both NL (Bax, 4.3-fold; P < 0.01; Bcl-2, 5.9-fold; P < 0.01) and IsCM (IsCM: Bax, 2.2-fold; P < 0.05; Bcl-2, 3.2-fold; P < 0.01) groups. The rate of apoptosis and the Bcl-2/Bax ratio independently correlated to graft survival in CR (activation of caspase-9: r = 0.87; P < 0.01; Bcl-2/Bax: r = 0.57; P = 0.05). Compared with native atherosclerosis, coronary arteries with CAV showed more medial apoptosis (7.8-fold; P < 0.01) and higher Bcl-2 levels (5.1-fold; P < 0.01) with lower Bax levels (threefold; P < 0.05) in the intima. These results indicate that abnormal Bcl-2 and Bax expression in myocardium and coronary arteries of cardiac allografts with CR is distinct from that in IsCM and suggest that balancing Bcl-2 to Bax in transplanted hearts promotes long-term graft survival.

Immunologic monitoring

The development of reliable in vitro assays that could allow the quantitation and characterization of anti-donor alloimmune responses has always been a goal in clinical transplantation, both to predict presensitization to the transplanted tissue and to be able to identify rejection without resorting to more invasive tests. With recent development in our understanding of transplantation biology and therapeutics, there is a real expectation that these tests may be used to identify tolerance as much as to predict rejection. The traditional limiting dilution assays still have a contribution to make and are being complemented by an array of tools, such as ELISpot, flow cytometry-based techniques, and microarray analysis. The assays that have been informative, to date, are discussed in this review. This information will lead, at least, to a better understanding of how and when the rejection process occurs. More interestingly, the objective is to apply this information to evaluate tolerance-inducing strategies or to identify patients that have become tolerant to their graft and can be weaned of immunosuppression. Of course sensitive, accurate and specific immunologic monitoring has applications well beyond the field of transplantation.

Accommodation in ABO-incompatible kidney allografts, a novel mechanism of self-protection against antibody-mediated injury

To elucidate the mechanism of self-protection against anti-donor blood-group antibody known as accommodation, we studied 16 human ABO-incompatible living-donor kidney transplant recipients at 3 and 12 months post transplantation. Both circulating anti-blood-group antibody and the target blood-group antigen in the graft were demonstrable in all patients after transplantation. Thirteen of 16 grafts had normal renal function and histology, while three grafts with prior humoral rejection demonstrated significant glomerulopathy and thus did not meet the criterion for accommodation. Using microarrays, we compared five 1-year protocol ABO-compatible renal graft biopsies to four accommodated ABO-incompatible graft biopsies. Significant alterations in gene expression in 440 probe sets, including SMADs, protein tyrosine kinases, TNF-alpha and Mucin 1 were identified. We verified these changes in gene expression using RT-PCR and immunohistochemistry. Heme oxygenase-1, Bcl-2 and Bcl-xl were not increased in ABO-incompatible grafts at any time-point. We conclude that accommodation is always present in well-functioning, long-surviving ABO-incompatible kidney transplants. This self-protection against antibody-mediated damage may involve several novel mechanisms including the disruption of normal signal transduction, attenuation of cellular adhesion and the prevention of apoptosis.

Mycophenolate mofetil-based immunosuppression and cytokine genotypes: effects on monokine secretion and antigen presentation in long-term renal transplant recipients

BACKGROUND

It has been suggested that increased monocyte responses might play a role in chronic allograft rejection.

METHODS

We investigated in vitro monokine responses in 112 patients with long-term stable kidney graft function (ST patients; n=80, non-mycophenolate mofetil [MMF]; n=32, MMF) and 25 patients with chronic renal transplant rejection (CR patients; non-MMF). Interleukin 10 and tumor necrosis factor (TNF)-alpha promoter gene polymorphisms were tested by polymerase chain reaction and sequence-specific primers; antigen-presenting capacity (AC) of monocytes was tested by incubation with staphylococcal superantigens (SEA, SEE, SED).

RESULTS

Although non-MMF-based immunosuppression in ST patients did not result in compromised AC or lipopolysaccharide (LPS)-stimulated monokine responses compared with healthy controls, we found MMF therapy to be associated with significantly reduced TNF-R1 expression on monocytes (P<0.001), suppressed AC (P<0.02, SED), and suppressed LPS-stimulated IL-1 beta, IL-10, and TNF-alpha secretion (P<0.01). Coinciding with a significantly higher steroid dosage in CR patients, IL-6 receptor and TNF-R1 expression on monocytes were down-regulated (P< or =0.02) and AC was suppressed in CR compared with ST (non-MMF) patients (P<0.01, SED; P<0.05, SEE). However, LPS-stimulated monokine secretion was not decreased or even enhanced (IL-6, granulocyte-macrophage colony-stimulating factor [GM-CSF]; P<0.05). Enhanced in vitro IL-10 responses (>500 pg/mL) were found predominantly in non-MMF-treated patients with the IL-10 genotype GCC (GCC: 23/62 [37%], non-GCC: 2/27 [7%], P<0.005; GCC and non-MMF: 22/47 [47%], GCC and MMF: 1/15 [7%], P<0.005].

CONCLUSION

Steroids and azathioprine did not sufficiently suppress monokine responses, whereas MMF treatment might inhibit chronic graft rejection because of suppression of TNF-R1 expression and vigorous inhibition of monokine secretion. MMF treatment may especially be indicated in patients with the IL-10 "high-producer" genotype GCC.

Anti-HLA class I antibody binding to airway epithelial cells induces production of fibrogenic growth factors and apoptotic cell death: a possible mechanism for bronchiolitis obliterans syndrome

Development of anti-HLA class I antibodies is associated with bronchiolitis obliterans syndrome (BOS) after lung transplantation. BOS is characterized histologically by significant fibrosis and airway epithelial cell (AEC) apoptosis. Thus, this study was designed to determine whether anti-HLA class I antibodies can activate AECs to produce growth factors and to undergo apoptosis. KCC-266 AECs were activated with the W6/32 anti-HLA class I monoclonal antibody. Proliferation and apoptosis levels were determined after 24, 48, and 72 hours. The induction of fibroblast and bronchial smooth muscle cell proliferation by anti-HLA class I activated AECs was assessed in the presence of neutralizing antibodies against various growth factors. The anti-HLA class I induced AEC proliferation after 24 hours followed by significant induction of apoptosis after 48 hours. Anti-HLA class I activated AECs produced soluble growth factors that stimulated fibroblasts but not bronchial smooth muscle cells. The stimulation of fibroblast proliferation was inhibited by antibodies against platelet-derived growth factor, heparin-binding epidermal growth factor, insulin-like growth factor 1, and basic fibroblast growth factor. The results from this study suggest that anti-HLA class I alloantibodies may play an important role in the pathogenesis of BOS by inducing proliferation, growth factor production, and apoptotic cell death in AECs.

The pathology of fresh and cryopreserved homograft heart valves: an analysis of forty explanted homograft valves

OBJECTIVE

Tissue degeneration reduces the durability of aortic and pulmonary homograft heart valves. Homograft valves can evoke cellular and humoral immune responses that might be detrimental to the valve tissue. Analyzing explanted homograft valves helps in understanding the different factors that eventually lead to tissue degeneration.

METHODS

A total of 40 homografts was acquired from patients whose grafts had been explanted because of stenosis (n = 22), insufficiency (n = 8), paravalvular leakage (n = 4), other technical problems (n = 4), noncardiac death (n = 1), and stenosis with endocarditis (n = 1). The period of implantation varied from 14 days to 16 years (median, 4 years). Cryopreserved valves (n = 31) were, in the majority, derived from beating-heart donors, whereas the fresh valves were sterilized with antibiotics and stored at 4 degrees C for an average of 32 days. Four unimplanted cryopreserved valves, 1 native aortic valve, and 1 native pulmonary valve were used as references. Analysis included macroscopy, light microscopy with routine hematoxylin and eosin staining (cellularity and tissue structure), and immunohistochemical studies to allow identification of macrophages (CD68) and T lymphocytes (CD3), endothelial cells, leukocyte adhesion molecules (CD54, CD106, and CD62E), and immunoglobulin (IgG) and complement factor (C3) depositions. In situ hybridization for the Y chromosome was performed in 10 cases, with host-donor sex mismatch, to distinguish between host and donor cells. The outcomes of histology and immunohistochemistry were related to clinical factors, such as implantation time and reason for explantation.

RESULTS

In the first year after implantation, a strong reduction in cellularity of the valve tissue was observed, with almost acellular tissues after 1 year. Trilaminar tissue architecture disappeared with the same speed, whereas endothelial cells were almost absent in all explants. Macrophages and T lymphocytes were encountered in 85% and 78% of the leaflets, respectively. Expression of leukocyte adhesion molecules was low in almost all grafts, and IgG and C3 depositions were not increased. Valve tissue cellularity consisted mainly of ingrown host cells when the implantation time exceeded 1 year.

CONCLUSIONS

During the first year of implantation, homograft valves rapidly lose their cellular components and normal tissue architecture. A low-grade inflammatory response was observed, but no convincing evidence of immune-mediated injury was found.

Induction of donor-specific allograft tolerance by short-term treatment with LF15-0195 after transplantation. Evidence for a direct effect on T-cell differentiation

A 20-day treatment with LF15-0195, a deoxyspergualine analog, induced long-term heart allograft survival in the rat without signs of chronic rejection. LF15-0195-treated recipients did not develop an anti-donor alloantibody response. Analysis of graft-infiltrating cells, IL10, TNFalpha, IFNgamma mRNA and iNOS protein expression in allografts, 5 days after transplantation, showed that they were markedly decreased in allografts from LF15-0195-treated recipients compared with allografts from untreated recipients. Surprisingly, spleen T cells from LF15-0195 recipients, 5days after grafting, were able to proliferate strongly in vitro, when stimulated with donor cells, but had reduced mRNA expression for IFNy compared with spleen T cells from untreated graft recipients. Furthermore, when T cells from naive animals were stimulated in vitro, using anti-CD3 and anti-CD28, LF15-0195 also increased T-cell proliferation in a dose-dependent fashion: however, these cells expressed less of the Th1 -related cytokines, IFNgamma and IL2, compared with untreated cells, suggesting that LF15-0195 could act on T-cell differentiation. In conclusion, we show here that a short-term treatment with LF15-0195 induced long-term allograft tolerance, decreasing the in situ anti-donor response, and we illustrate evidence for the development of regulatory mechanisms.

Transplantation-induced endothelial dysfunction as studied in rat aorta allografts

BACKGROUND

Clinical evidence indicates that vascular endothelial cell (EC) dysfunction occurs early after transplantation (Tx) and initiates chronic graft vasculopathy. This study explored this phenomenon in rat aorta Tx using the stringent Dark Agouti (DA)-to-Lewis (LEW) and the weak Fischer 344 (F344)-to-LEW strain combinations.

METHODS

Donor abdominal aortae were orthotopically grafted into LEW rats. At post-Tx days 7, 14, 28, and 56, grafts were collected to assess changes in EC morphology (en face silver staining) and EC function, i.e., vasodilatory response to acetylcholine (ACH) after phenylephrine (PHE) precontraction; changes in vascular smooth muscle cell (VSMC) alpha-actin (western blotting), degree of apoptosis (caspase-3 activity), and morphology.

RESULTS

In DA allografts, VSMC and EC dysfunctions developed concomitantly and were completed at 14 days post-Tx, most likely due to the EC and alpha-actin-positive VSMC loss. Meanwhile, allografts revealed markedly increased caspase-3 activity. Neointima formation, restricted to the edges of allografts at day 28, covered the entire allografts by day 56 post-Tx. In F344-allografts, VSMC function was maintained up to day 14 post-Tx, whereas ACH-induced relaxation was reduced by 50% at day 7 and abolished at day 14. EC denudation was not seen up to 56 days post-Tx, despite prominent leukocyte adhesion. Neointima formation was not detected at day 28 post-Tx but appeared along the entire allografts at day 56 post-Tx.

CONCLUSIONS

These results confirm that Tx-induced EC dysfunction precedes the development of vasculopathy in rat aorta allografts and suggest that this early phenomenon can be best studied in the F344-to-LEW strain combination.

Epitope mapping of the indirect T cell response to allogeneic class I MHC: sequences shared by donor and recipient MHC may prime T cells that provide help for alloantibody production

Indirect allorecognition occurs when T cells recognize donor MHC presented as peptide epitopes by recipient APC, but the precise nature of the epitopes involved remains unclear. Rejection of rat MHC class I-disparate PVG.R8 (RT1.A(a)) grafts by PVG.RT1(u) (RT1.A(u)) recipients is mediated by indirectly restricted CD4 T cells that provide help for the generation of alloantibody. In this study, epitope mapping was performed using a functionally relevant readout (alloantibody production) to identify key peptides that prime an indirect alloimmune response, leading to graft rejection. PVG.RT1(u) rats were immunized with a series of overlapping 15-mer peptides (peptides 1-18) that spanned the alpha1 and alpha2 domains of the RT1.A(a) molecule. Several peptides were able to accelerate both the alloantibody response to the intact RT1.A(a) Ag and PVG.R8 heart graft rejection. An immunodominant epitope was identified within the hypervariable region of the alpha1 domain. Fine mapping of this region with a second series of peptides overlapping by single amino acids confirmed the presence of an eight-amino acid core determinant. Additional "subdominant" epitopes were identified, two of which were located within regions of amino acid homology between the RT1.A(a) and RT1.A(u) molecules and not, as had been expected, within other hypervariable regions. The contribution of self-epitopes to indirect allorecognition was emphasized by the demonstration that i.v. administration of a 15-mer peptide encompassing one of the subdominant self-determinants diminished the recipient's ability to mount an alloantibody response on challenge with intact A(a) alloantigen. Our findings suggest that cryptic self-epitopes recognized by autoreactive T cells may contribute to allograft rejection and should be considered when designing novel strategies for inducing tolerance to alloantigen.

Endoluminal smooth muscle cell seeding limits intimal hyperplasia

PURPOSE

Intimal hyperplasia is one of the main responses of the vascular wall to injury. In the current study, we tested the hypothesis that endoluminal seeding of host syngeneic vascular cells could limit intimal hyperplasia induced by either mechanical deendothelialization or chronic allograft rejection in rat aorta.

METHODS

An experimental model of in situ seeding of syngeneic endothelial cells, smooth muscle cells (SMCs), and fibroblasts (FIBs) was used in mechanically deendothelialized and allografted aortas. In a preliminary study, the ability of the three cell types (n = 5 per group) to seed on the deendothelialized luminal surface of the aortic wall was evaluated after 2 days, with the use of fluorescent PKH as marker. In the first model, the abdominal aorta of Lewis rats was deendothelialized (n = 6) or deendothelialized and seeded with either SMCs (n = 6) or FIBs (n = 6) before flow was restored. In the allograft model, aortas were harvested from dark agouti rats and orthotopically grafted in Lewis receivers, directly (n = 6) or after deendothelialization. Deendothelialization was performed alone (n = 6) or associated with the seeding of similar host (Lewis) syngeneic SMCs (n = 6) or FIBs (n = 6). Results were evaluated at 2 months with histologic and morphometric methods.

RESULTS

SMCs and FIBs were able to adhere in situ to the deendothelialized aortic wall, whereas endothelial cells were not. In mechanically deendothelialized aortas, the seeding of syngeneic SMCs led to a significant reduction in intimal thickness compared with deendothelialized aortas or FIB-seeded aortas (26.9 +/- 1.7 microm vs 55.5 +/- 1.7 and 56.7 +/- 1.7 microm, respectively), and a lower nuclear content (382.2 +/- 35.7 microm(2) vs 779.6 +/- 65.9 and 529.6 +/- 24.3 microm(2), respectively) of neointima. After SMC seeding, intimal hyperplasia was richer in elastin, whereas after FIB seeding it was richer in collagen. In allografts, the seeding of syngeneic SMC led to a significant reduction in intimal thickness compared with control aortas, deendothelialized aortas, or FIB-seeded aortas (31.6 +/- 1.1 microm vs 88.55 +/- 2.8, 74.6 +/- 2.9, and 85.7 +/- 2.6 microm, respectively), and a reduced nuclear content of the neointima (444.9 +/- 23.4 microm(2) vs 1529.1 +/- 116, 972.3 +/- 50, and 645.2 +/- 32.4 microm(2), respectively). Differences observed in the extracellular matrix composition were equivalent to those observed in the mechanically deendothelialized model.

CONCLUSIONS

Our results suggest that endoluminal seeding of syngeneic SMCs can be effective in reducing intimal hyperplasia both in a deendothelialization model and in arterial allografts. SMC and FIB endoluminal seeding led to a significatively different accumulation of extracellular matrix in the intima.