820 PART III Pathology stimulation of circulating host immune cells that encounter donor MHC antigens on allograft cell surfaces. T-Cell Activation T-cell activation is essential for allograft rejection. T-cell activation is associated with nuclear translocation of specific transcription factors that regulate expression of genes criti- cal for T-cell function. NF-kB plays the central role in this process. The activation of T cells is a key start mechanism of immune response and requires two distinct, but synergis- tic, signals. The first signal is provided by a specific antigen and is delivered via the T-cell receptor. The second signal (costimulatory signal) is not antigen specific. Indeed, many T-cell molecules may serve as receptors for costimulation. The most well characterized costimulatory molecule is CD28, which has two ligands (B7-1 [CD80] and B7-2 [CD86]) that are expressed primarily on APCs. Another molecule, CTLA-4, is similar to CD28 and is also expressed on T cells. Although CTLA-4 binds B7-1 and B7-2, it trans- mits an inhibitory signal that serves to terminate the immune response. Cellular and Humoral Mechanisms of Allograft Rejection One or more attacks of acute cellular (Figure 1) or humoral (antibody-mediated) rejection (Figure 2) usually occur in almost half of the kidney transplant recipients despite active immunosuppressive strategies. Until recently, most studies on the mechanisms of renal allograft rejection have focused on the central role of T cells and of other cel- lular mechanisms of tissue injury. It has been established that CD4 T cells are crucial in initiating most acute rejection episodes, and that alloactivated CD4 T cells, cytotoxic CD8 T cells, monocytes/macrophages, and NK (natural killer) cells play a major role in cell-mediated mechanisms that eventually result in allograft destruction. Perforin and granzyme B are two proteins that are present in the cyto- plasmic granules of cytotoxic T cells and NK, cells which are an integral part of the effector mechanisms of cell- mediated allograft rejection. In recent years, it has also become increasingly appreciated that detection of anti-MHC donor specific antibodies (DSA) de novo after transplanta- tion is associated with rejection due to antibody-mediated effector mechanisms of tissue injury. The identification of the complement fragment C4d as a specific marker for humoral rejection in peritubular capillaries (PTCs) of renal allograft biopsies has helped to define and characterize these syndromes. Cytokines and Cell Adhesion Molecules in Transplant Immunity Cytokines are any of numerous low-molecular-weight proteins that regulate the intensity and duration of the immune response by exerting a variety of effects on lym- phocytes and other immune cells. A diversity of cytokines, each with many functions, is involved in an immune response. While IL-12 facilitates differentiation towards the Th1 phenotype and IL-4 towards the Th2 phenotype, other cytokines such as INF-8 and IL-2 secreted by the Th1 cells promote cell-mediated immune responses, and IL-4, IL-6, and IL-7 released by Th2 cells are important in B cell maturation. IL-2 and IFN-g play crucial roles in graft rejection. They are important for recruitment, activation, and proliferation of various leukocytes, for the induction or upregulation of cell adhesion molecules and MHC molecules, and for mediating communication between leukocytes and parenchymal cells. Therefore, IL-2 has been studied as a potential target for suppression of graft rejec- tion. The complexity of the cytokine network, particularly the plethora of cytokines and their overlapping functions, is a major obstacle in achieving this objective. Cell adhesion molecules, particularly intercellular adhe- sion molecule-1 (ICAM-1) and vascular cell adhesion Figure 1 Acute cellular rejection. Lymphocytes (L) infiltrate beneath endothelium (E) with edema of intima (I) and subintimal layers (B). (H ¥ E, original magnification 100¥.) (see color insert) Figure 2 Acute humoral rejection. Fibrinoid necrosis (N) of the thick- ened arterial wall surrounded by polymorphonuclear and lymphoid cell infiltrates (L). (H ¥ E, original magnification 400¥.) (see color insert) CHAPTER 122 Microvasculature in Kidney Transplant Rejection 821 molecule-1 (VCAM-1), are also key regulatory molecules in immune responses. They are important in migration and localization of leukocytes into tissues as well as in a variety of cell-to-cell interactions that include signaling between cells and even cell-mediated cytotoxicity. The expression of these molecules, which occurs in a sequential fashion, is important for orchestrating the various steps in graft rejec- tion, though the actual sequence of events and their under- lying mechanism is not yet clear. A brief summary of the role of some cytokines involved in allograft rejection is given in Table I. Microvasculature and Renal Transplant Rejection Endothelium of the allograft vasculature is the interface between an allograft and the recipient’s immune system. In this boundary position, endothelial cells may play important roles in the afferent and efferent phases of allograft rejec- tion. The expression by endothelial cells of granule mem- brane protein-140 (GMP-140/P-selectin) and endothelial leukocyte adhesion molecule-1 (ELAM-1/E-Selectin) increases tissue factor activity, augments secretion of plas- minogen activator inhibitor, and decreases thrombomodulin, contributing to hyperacute rejection. Similarly, endothelial cells may actively participate in acute cellular rejection and in the development of transplant-associated arteriopathy as a result of induction of antigen-presenting function (i.e., MHC class 2 expression), upregulation of adhesion mole- cules for lymphocytes and monocytes, and release of platelet-derived growth factors. Therefore, endothelial cell functions, which are important for normal inflammatory responses and vessel behavior, may be pathogenic in the allograft [2]. Microvascular Injury in Hyperacute and Accelerated Kidney Transplant Rejection Hyperacute rejection occurs within minutes to hours after the vascular clamps to the transplanted organ are released. This dramatic event is caused by preexisting cytotoxic, anti- HLA class 1 (IgG) or anti-ABO blood group antibodies (IgM) in the recipient. The antibodies bind to the endothe- lial surface of the arterioles on the graft, activate comple- ment, and lead to severe microvascular injury including thrombosis and obliteration of the graft vasculature. The endothelial cells are stimulated to secrete von Willebrand factor (vWF), which mediates platelet adhesion and aggre- gation. Complement activation initiates coagulation cascade and the generation of multiple inflammatory mediators. Eventually, transplanted tissue suffers irreversible ischemic damage. Hyperacute rejection is mediated by antibodies against alloantigens that have appeared in response to previ- ous exposure to these antigens through blood transfusion, prior transplantation, or multiple pregnancies. Pathologic findings show fibrin thrombus formation, margination of neutrophils, and ultimately fibrinoid necrosis of the vessel walls. The transplant may become flaccid or cyanotic and hard and may rupture. Accelerated acute rejection taking place within 1 to 4 days after transplantation occurs when the recipient has been sensitized by prior interaction with graft antigen, gen- Table I The Role of Some Cytokines and Chemoattractive Molecules in Renal Transplant Rejection. Cytokine Function in allograft rejection IL-1 Causes neointimal formation and pathogenesis of chronic rejection IL-2 Enhances all types of allograft rejection IL-4 Promotes a delay in vasculopathy in the graft IL-5 Mediates transplant vasculopathy IL-10 Prevents ischemia–reperfusion injury and decreases acute rejection IL-15 Activates allospecific CD8 T cells during acute rejection IL-16 Plays an activation role rather than an inhibition of anti-graft reaction IL-17 Stimulates early alloimmune responses IL-18 Plays the activation role in acute rejection IFN-g Promotes acute rejection of kidney allografts TNF-a Participates in pathogenesis of acute and chronic rejection TGF-b1 Expression is linked with chronic vasculopathy VEGF Influences adhesion and migration of leukocytes across the endothelium MCP-1 Associated with premature kidney graft failure ICAM-1 and VCAM-1 Early leukocyte and lymphocyte recruitment in the microvasculature of rejecting allograft, costimulation T cell activation PDGF Mediates mesenchymal cell proliferation in chronic rejection M-CSF Promotes macrophage recruitment and proliferation 822 PART III Pathology erally by prior transplantations but also by transfusions, and is thought to represent an immunologic memory response to prior sensitization. This type of rejection may represent a combination of cellular and antibody-mediated injury, but the cellular infiltration may not be as intensive as with acute rejection. Renal Microvasculature and Acute Transplant Rejection Acute renal graft rejection is able to activate human endothelial cells leading to upregulation of mRNAs coding for VCAM-1 and ICAM-1 and plays a direct role in the pathogenesis of acute rejection [3]. Endothelial deposition of the complement split product C4d is an established marker of antibody-mediated acute renal allograft rejection. Cells of the monocyte/macrophage system have active contribution to acute allograft destruction. Monocytes are recovered from both the central and the marginal blood pool by perfusing either the recipient’s circulation or the allograft vasculature. During allograft rejection MHC class 2 mole- cules, CD161 (NKR-P1A), CD62L, and CD8, are upregu- lated, while CD4 and CD43 are down-modulated. Activated monocytes participate in the kidney allograft destruction by directly damaging endothelial cells and by promoting intravascular coagulation. Recruitment of leukocytes during immune responses requires the coordinate expression of adhesion molecules in concert with chemokines and their receptors. The Duffy antigen receptor for chemokines (DARC) binds multiple chemokines and is expressed on postcapillary venules in the normal kidney. The chemokine receptor CCR5, which shares the ligand regulated upon activation, normal T-cell expressed and secreted (RANTES) with DARC, is expressed by infiltrating T cells in the renal interstitium. DARC is involved in the attraction of CCR5-positive cells. Therefore, the increased number of DARC-positive venules in areas of interstitial injury and the co-localization with CCR5-positive infiltrating leukocytes indicate a role for endothelial DARC expression during leukocyte adhesion and interstitial infiltration [4]. Histopathology of the allo- grafts reveals edema and interstitial cellular infiltration as well as tubulitis, and necrosis and hemorrhage in severe cases. Destruction PTCs and tubules accompanied by dis- ruption of basement membrane (BM) occurred with capil- laritis or tubulitis in areas with a severe cellular infiltrate. Glomerular changes notably included swelling of the tufts due to hypercellularity, which is consistent with transplant glomerulitis. The intrarenal arteries exhibit intimal or in severe cases transmural mononuclear cell inflammation with or without fibrinoid necrosis of vessel wall (the latter often with antibody mediated rejection) [5]. Microvasculopathy during Chronic Kidney Transplant Rejection Chronic rejection is associated with the development of interstitial fibrosis and PTC, endothelial cell, and tubular epithelial cell death associated with CD3+ cell infiltration (Figure 3). During the development of chronic rejection, capillaritis of PTCs and tubulitis are maintained by persist- ent T-cell infiltration, and the remaining PTCs and tubules exhibit progressive atrophy with thickening and/or lamina- tion of BM. Then identifiable PTCs and tubules are lost in areas of interstitial fibrosis. Proliferating myofibroblasts accumulate around PTCs and tubules and in interstitium, and there is widespread interstitial fibrosis. The contribution of alloantibody-dependent immune reactions to chronic rejection is being increasingly appreciated. Influence of Ischemic Reperfusion Injury on Renal Graft Function and Kidney Microvasculature All allografts undergo some degree of ischemic reper- fusion injury (IRI) during transplantation. IRI causes renal vascular endothelial damage and plays an important role in kidney transplant pathophysiology. IRI induces allograft endothelial cell swelling, alters endothelial cell–cell connection, and alters endothelial cell–basement membrane attachment. Functional consequences of these morphological changes include altered vascular reactivity, increased leukocyte adherence and extravasation, altered coagulation due to loss of normal endothelial function and/or barrier, and increased interstitial edema. Increased levels of gene transcripts involved in cellular adhesion, chemotaxis, apoptosis, and monocyte recruitment and activation dominate the immediate postreperfusion state. T cells are a fundamental link between IRI injury and alloimmunity. This phenomenon is highlighted by data demonstrating that T-cell depletion can improve the course of experimental renal IRI [6]. Damage during IRI predis- poses to acute and chronic rejection. Figure 3 Chronic rejection. Lymphocyte (L) infiltration and fibrosis of intima (F). There is perivascular sclerosis and edema (S). Endothelial cells are swollen and some are pyknotic (E) (Mallory, original magnification 400¥). (see color insert) CHAPTER 122 Microvasculature in Kidney Transplant Rejection 823 Microvascular Injury Caused by Immunosuppressive Therapy Calcineurin inhibitors such as cyclosporine A (CyA) and tacrolimus (FK506) drastically enhance the survival of organ transplants and recipients. But they themselves can affect endothelial function in renal transplant patients, as administration of these immunosuppressants is correlated with a high incidence of transplant arteriolopathy. The endothelium-dependent and -independent vasodilation of the patients on FK506 is better preserved than in patients on CsA therapy. Vascular endothelial cells naturally express a death factor, Fas ligand, that inhibits detrimental leukocyte infiltration. It has been shown that CyA and FK506 down- regulate Fas ligand expression on endothelial cells with accompanying decrease in the cytotoxicity toward Fas- bearing cells. These data suggest a mechanism by which immunosuppressive treatment contributes to atherogenesis [7]. Development of thrombotic microangiopathy has been associated with CyA and FK506 toxicity. Glossary Allograft: A transplant of an organ or tissue that is donated either by a genetically matched relative of the patient or by an unrelated (but geneti- cally similar) donor. Cytokines: Nonantibody proteins secreted by inflammatory leuko- cytes, and some nonleukocytic cells, that act as intercellular mediators. They differ from classical hormones in that they are produced by a number of tissue or cell types rather than by specialized glands. They generally act locally in a paracrine or autocrine rather than endocrine manner. Endothelium: The layer of epithelial cells that lines the cavities of the heart and of the blood and lymph vessels, originating from the mesoderm. Lymphokines: Soluble protein factors generated by activated lympho- cytes that affect other cells, primarily those involved in cellular immunity. Rejection: Any immune process leading to the destruction or detach- ment of a graft or other specified structure. References 1. Complete sequence and gene map of a human major histocompatibility complex The MHC sequencing consortium. Nature (1999). 28, 921–923. 2. Sedmak, D. D., and Orosz, C. G. (1991). The role of vascular endothe- lial cells in transplantation. Arch. Pathol. Lab. Med. 115(3), 260–265. 3. Lucchiari, N., Panajotopoulos, N., Xu, C., Rodrigues, H., Ianhez, L. E., Kalil, J., and Glotz, D. (2000). Antibodies eluted from acutely rejected renal allografts bind to and activate human endothelial cells. Hum. Immunol. 61(5), 518–527. 4. Segerer, S., Regele, H., MacK, M., Kain, R., Cartron, J. P., Colin, Y., Kerjaschki, D., and Schlondorff, D. (2000). The Duffy antigen receptor for chemokines is up-regulated during acute renal transplant rejection and crescentic glomerulonephritis. Kidney Int. 58(4), 1546–1556. 5. Haishima, A., Kawakami, Y., Mizuno, S., Kageyama, T., Muto, M., Suzuki, T., Inoue, K., and Shirota, K. (2002) Acute vascular and inter- stitial rejection following renal allograft transplantation in dogs. J. Vet. Med. Sci. 64(12), 1137–1140. 6. Yokota, N., Daniels, F., Crosson, J., and Rabb, H. (2002). Protective effect of T cell depletion in murine renal ischemia-reperfusion injury. Transplantation 74(6), 759–763. 7. Sata, M., and Walsh, K. (1999). Cyclosporine downregulates Fas ligand expression on vascular endothelial cells: implication for accelerated vas- culopathy by immunosuppressive therapy. Biochem. Biophys. Res. Com- mun. 263(2), 430–432. Further Reading Inston, N., and Cockwell, P. (2002). The evolving role of chemokines and their receptors in acute allograft rejection. Nephrol. Dial. Transplanta- tion 17, 1374–1379. The article is concentrated on the expression of chemokine receptors that direct the trafficking of alloactivated T cells into the graft in response to local production of chemokines, initiallyby resident cells. There is now deep interest in this area that reflects the recent identification of restricted chemokine–receptor interactions as key functional events in T-cell recruitment and potential therapeutic targets for the prophylaxis of acute allograft rejection. Shimizu, A., Colvin, R. B., and Yamanaka, N. (2000). Rejection of per- itubular capillaries in renal allo- and xeno-graft. Clin. Transplantation 14, 6–14. The review shows that microvasculature plays an important role in the pathogenesis of humoral- and cell-mediated renal allograft rejection. PTC endothelium expresses the MHC antigens in the resting phase, as does the glomerular capillary endothelium. Thiru, S., and Waldmann, H. (eds.) (2001). Pathology and Immunology of Transplantation and Rejection. Boston: Blackwell Science. This textbook offers a good insight into various aspects of organ transplantation. Capsule Biography Vladimir Savransky, M.D., Ph.D., received his medical school and surgical training in St. Petersburg, Russia. He is currently a Postdoctoral Research Fellow in the Division of Nephrology, Johns Hopkins University School of Medicine. Mark Haas, M.D., Ph.D., received his medical school training at Duke University and specialization in kidney pathology at Yale. He is currently Professor in the Department of Pathology, Johns Hopkins University School of Medicine. Hamid Rabb, M.D., received his medical school training at McGill Uni- versity and specialization in kidney diseases at Harvard. He is currently Director, Transplant Nephrology and Associate Professor of Medicine, Johns Hopkins University School of Medicine. [...]... endothelial cells to express adhesion molecules such as P -and E-selectin and intercellular adhesion molecule-1 (ICAM-1) Since the neutrophils are also activated to express those ligands such as P-selectin glycoprotein ligand-1 (PSGL-1), CD11b/ CD 18, or L-selectin, activated neutrophils accumulate in the lung Activated neutrophils starts rolling and sticking on the surfaces of endothelial cells While... Physiol 88 , 88 8 89 3 Tasaki, O., Mozingo, D W., Ishihara, S., Brinkley, W W., Johnson, A A., Smith, R H., Srivastava, O., Mason, A D., Jr., Pruitt, B A., Jr., and Cioffi, W G., Jr (19 98) Effect of Sulfo Lewis C on smoke inhalation injury in an ovine model Crit Care Med 26, 12 38 1243 9 Katahira, J., Murakami, K., Schmalstieg, F C., Cox, R., Hawkins, H., Traber, L D., and Traber, D L (2002) Role of anti-L-selectin... pulmonary artery and bronchial arteries, a branch of the systemic arterial system 83 5 Copyright © 2006, Elsevier Science (USA) All rights reserved 83 6 PART III Pathology inhalation Activation of these cells was prevented by treatment with an antibody to L-selectin Activation of Akt/PI3 also inhibits neutrophil apoptosis by increasing transcription of the anti-apoptotic proteins Mcl-1 and Bcl-2, and also inhibiting... events (leukocyte and platelet accumulation and adherence) as determinants in the development of primary graft dysfunction Leukocyte–endothelial cell interaction seems to be mediated classically by involvement of P-selectin in leukocyte rolling and Mac-1 and ICAM-1 in leukocyte firm adhesion, because blockade of selectins, b2-integrins, and ICAM-1 has been shown effective in reducing post-transplant leukocyte... septic shock with concomitant microvascular leak syn- PART III Pathology drome, that it is possible to maintain plasma volume by the artificial colloids modified fluid gelatin 4 percent and 8 percent (MFG4%, MFG8%), and 6 percent HES 200/0.5, but not with Ringer’s solution despite increased microvascular permeability [8] Theoretically, in the presence of a microvascular leak— which allows the escape of albumin—one... contributes to the manifestation of both no-reflow and reflow-paradox in post-transplant reperfusion injury Endothelin-1 seems to be the “bad guy” in this scenario This view is supported by the fact that endothelin-1 and bigendothelin concentrations are elevated in liver graft tissue during cold storage and reperfusion, and that the cold storage–induced endothelin-1 release is associated with an increase... deactivation anti-proinflammatory mediator treatment antioxidant treatment endothelin A receptor blockade adhesion molecule blockade ischemic preconditioning (+++) Targets and potential novel treatment strategies to attenuate microcirculatory reperfusion injury after whole-organ cold storage and transplantation 84 8 PART III Pathology thermodiffusion analysis [9], near-infrared spectrometry, and orthogonal... Otto-Goetze-Award of the Bavarian Society of Surgery in 1994 and the Calogero-Pagliarello-Award of the University of Saarland in 2000 Her research focus is microcirculatory dysfunction and mechanisms in shock, sepsis, ischemia–reperfusion, and microvascular thrombosis Her work is supported by grants from the Deutsche Forschungsgemeinschaft SECTION P Periodontal Disease CHAPTER 126 The Pathobiology of... ischemia–reperfusion-induced endothelial cell killing and detachment, and improves the quality of early microvascular reperfusion The effectiveness of the rinse solution may additionally be increased by prewarming the solution before infusion into the donor organ As demonstrated in rat liver PART III Pathology and intestine, prewarming of either Carolina rinse or Ringer’s lactate indeed reduces post-transplant no-reflow,... involved: Q = K[(Pc - Pi) - s(pc - pi)] where Q is the net flux of fluid out of the microvasculature, K is the filtration coefficient (an index of microvascular permeability to small molecules), Pc and Pi are the hydrostatic pressures in the capillary and interstitial spaces, respectively, pc and pi are the corresponding colloid osmotic pressures, and s is the reflection coefficient; an index of the microvascular . phenotype and IL-4 towards the Th2 phenotype, other cytokines such as INF -8 and IL-2 secreted by the Th1 cells promote cell-mediated immune responses, and IL-4, IL-6, and IL-7 released by Th2. CTLA-4, is similar to CD 28 and is also expressed on T cells. Although CTLA-4 binds B 7-1 and B 7-2 , it trans- mits an inhibitory signal that serves to terminate the immune response. Cellular and. of granule mem- brane protein-140 (GMP-140/P-selectin) and endothelial leukocyte adhesion molecule-1 (ELAM-1/E-Selectin) increases tissue factor activity, augments secretion of plas- minogen activator