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Copyright C Blackwell Munksgaard 2002

American Journal of Transplantation 2002; 2: 195–200 Blackwell Munksgaard

ISSN 1600-6135

Editorial

Call for Revolution: A New Approach to Describing Allograft Deterioration Philip F. Halloran Division of Nephrology & Immunology, 250 Heritage Medical Research Centre, University of Alberta, Edmonton, Alberta, T6G 2S2, Canada, [email protected] I propose a set of definable entities in the renal transplant course, eliminating the need for the term ‘chronic rejection’. The status of a renal transplant can be defined by the presence and extent of rejection (T-cell-mediated or antibody-mediated); allograft nephropathy (parenchymal atrophy, fibrosis, and fibrous intimal thickening in arteries); transplant glomerulopathy; specific diseases; and factors which could accelerate progression. The level of function and the slope of the loss of function should be separately determined. This approach can be applied both in research and in clinical practice, and can be adapted to other organ transplants.

Received 7 January 2002, accepted for publication 18 January 2002

frustrated by the tendency to regard chronic allograft nephropathy as a synonym for chronic rejection, with all of its ambiguity. This name game obscures an important issue: some deteriorating grafts are experiencing active injury mediated by the alloimmune response (rejection), and some are not. Given that we have many new treatments to suppress alloimmune mechanisms, it is critical to identify grafts experiencing rejection. We need a precise language to convey this information. I propose that we abandon the term chronic rejection, and replace it with precise, useful terms. Indeed, we should avoid the terms ‘acute’ and ‘chronic’, and concentrate on the existence and the details of rejection. I will illustrate the argument with clinical kidney data, which have the advantage of large numbers, long follow-up, inclusion of many well-matched grafts and live-donor grafts, and quantitative measures of function. Nevertheless the argument can be adapted for other organ transplants. The present discussion will focus on clinical data, not experimental models, and on (death censored) graft survival and pathology, not on patient survival.

Introduction History ‘One should not increase, beyond what is necessary, the number of entities required to explain anything.’ William of Occam ‘Everything should be made as simple as possible, but not simpler.’ Albert Einstein The recent Banff consensus conference on allograft pathology (see meeting report by Racusen et al. in this issue) is a good occasion to re-examine our approach to late graft events, in the revolutionary spirit of the painting by Delacroix on the cover of this issue. Late loss of organ transplants is a major problem in transplantation, second in importance only to the shortage of available organs. But the concepts and nomenclature concerning deteriorating graft function are outdated and misleading. In particular, the term ‘chronic rejection’ has become so encrusted with different meanings as to no longer be useful. The chronic rejection concept fails to distinguish between the presence of an active immune response (rejection) and the state of the transplanted tissue (e.g. fibrosis and atrophy). Attempts to replace it by a new term (in kidneys, chronic allograft nephropathy) have been

Chronic rejection of kidney transplants is commonly defined as an alloimmune response that produces slow deterioration of graft function with characteristic pathology: tubular atrophy (TA), interstitial fibrosis (IF), and fibrous intimal thickening of arteries (FIT) – the ‘TA/IF/FIT triad’. The key concept is that chronic rejection is an immune response, different from acute rejection, even late acute rejection. Unfortunately in few cases does the clinician establish that TA/IF/FIT and loss of function are accompanied by an active alloimmune response. Thus the above definition of chronic rejection is actually a belief system. Some definitions of chronic rejection include a requirement for relentless progression. This seems circular, since we do not usually define a disease by its rate of progression. Moreover, the rate of progression in failing kidneys is unpredictable (1). The idea of slow or ‘chronic’ immune-mediated graft destruction (rejection) was established in experimental studies by 1960 (2). The first case of late failure of an allogeneic kidney transplant was reported in 1955 (3), failing after 5 1/2 months with arterial obliterative lesions. Similar cases were identified 195

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in the 1960s (4, 5), often with glomerulopathy (6, 7), and in some cases with an ongoing alloantibody response (5). Then came the inversion, which can be stated as follows: ‘If the immune response can result in TA/IF/FIT, then TA/IF/FIT in a transplant constitutes a priori evidence of an immune response.’ Thus grafts with damage due to previous injury, usually without glomerulopathy and with no evidence of a continuing immune response, came to be called chronic rejection. Chronic rejection came to refer to all nonspecific late graft dysfunction, even that due to donor age (8). The recognition of rapidly progressive coronary artery disease in heart transplants reinforced the conviction that late graft deterioration over months was primarily due to arterial injury. The heart transplant experience was different in that the parenchyma did not necessarily manifest diffuse changes (9). In liver transplantation a progressive form of destruction of the biliary tree (‘vanishing bile duct syndrome’) was observed but is now uncommon (10). Bronchiolitis obliterans in transplanted lungs was recognized soon after the introduction of heart-lung and lung transplants (11, 12), and today constitutes a major problem (13). From the outset clinicians suspected that obliterative bronchiolitis reflected multiple injuries but that rejection was often an important component.

The Problem The term ‘chronic rejection’ no longer conveys a meaning that is clear to all observers. We have reached an impasse because of language. This happens in many fields: language can limit the development of a science because it prevents the precise definition of problems. Some of this is inherent in the ambiguity of the adjective ‘chronic’ (from the Greek khronikos ‘to do with time’, from khronos ‘time’). ‘Chronic’ may be used to describe a mechanism of injury as persistent or recurrent (which are not the same), or the effects of the injury on the organ (long-lasting or irreversible). Pathologists often use ‘chronic’ to imply a characteristic appearance: scarring and atrophy.

The Human Renal Transplant Experience: the Five Factors That Determine Graft Survival Given the above problems, we should return without prejudice to the human data. As detailed in recent reviews (14– 16), the variables associated with graft failure (death censored) can be simplified to five groups of factors (Table 1): 1. Donor age and tissue quality. Donor age has a powerful impact on graft survival. Long-standing stresses such as hypertension and diabetes are also important. Old kidneys have poorer initial function, more delayed graft function (DGF), more rejection in some studies, poorer GFR, more allograft nephropathy. Older kidneys are more sensitive to 196

Table 1: Five factors that influence renal graft survival 1. 2. 3. 4.

Donor age and age-related diseases Brain-death-related stresses Preservation and implantation stress Rejection a. T-cell mediated b. Alloantibody mediated 5. Post-transplant stresses in the recipient environment

rejection (17), but many effects of donor age are probably not due to rejection (18). 2. Brain death. The surprising magnitude of the differences between live donor and cadaver donor kidney transplants, equivalent to the effect of HLA matching, became apparent as the live unrelated donor data accumulated (19). The differences seem most related to brain death, although other differences can be implicated: selection, shorter preservation time, elective surgery, etc. 3. Preservation and implantation injury. As recently discussed (20), injury occurs during organ removal, cold preservation, vascular anastomosis, and in the hours after the transplant due to reperfusion. Even the process of organ cooling may cause injury (21). 4. Immune-mediated injury: rejection. T-cell-mediated rejection increases the probability of graft loss, particularly severe rejection with endothelial injury. Antibody-mediated rejection is less common but also is associated with a high rate of graft loss. Both T-cell-mediated and antibodymediated rejection can occur late, especially in noncompliant patients, and can run a persistent or recurrent course. The new immunosuppressives and HLA matching probably exert their benefits by lowering the probability of T-cell-mediated and antibody-mediated rejection. 5. Post-transplant stresses and systemic stresses in the recipient environment. For kidney, these include infectious agents (e.g. BK polyoma virus), hypertension, proteinuria, drug toxicity, and potentially hyperlipidemia, cytomegalovirus (CMV), and very large body mass. Some influences may affect the tissue by increasing the frequency of rejection, but most of these effects are probably not mediated by rejection. Individual population factors may impact more than one of these groups of factors. For example, African-American donors and recipients carry different risks from others, which are partly immune and partly non-immune. The general medical condition of the host, including age and disease in other organ systems, can affect the health of the graft, as well as patient survival. Even the choice of immunosuppressive drugs also has potentially complex effects, through rejection, drug toxicity, hypertension, and lipid disorders. Hunsicker recently introduced a new approach to the human American Journal of Transplantation 2002; 2: 195–200

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renal transplant population (22). He analyzed renal function (estimated glomerular filtration rate, GFR) in the renal transplant population database. He defined two parameters of function: the level of function at 6 months (GFR) and the rate of decline of function beyond 6 months (slope of GFR). The mean GFR was about 60 mL/min and the mean slope was ª2.5% per year in the whole population. This analysis indicates the rate of decline of GFR is independent of the absolute level of GFR, confirming the previous findings for native kidneys in the Modification of Diet in Renal Disease study (23). This refutes the theory that kidneys with reduced GFR automatically deteriorate more quickly due to hyperfiltration. The Hunsicker approach invites us to reassess transplant populations by the level of function achieved and the durability of function, rather than by survival and half-life, and provides a good starting point for re-thinking the problem of graft deterioration.

Enter William of Occam This 14th Century Franciscan monk advocated choosing the simplest explanation possible. To comply with Occam’s razor, and Einstein’s warning against oversimplification, we must choose the least number of entities which can describe the problem. We need five entities (Table 2): rejection, allograft nephropathy, allograft glomerulopathy, specific diseases, and accelerating factors: 1. Rejection: an ongoing alloimmune response causing tissue injury. Injury can be defined either by pathology or

Table 2: The five entities that describe the status of the renal allograft 1. Rejection: graft injury due to: a. T-cell-mediated rejection: tubulitis, endothelialitis, interstitial infiltrate b. Alloantibody-mediated rejection 2. Allograft nephropathy: reduced function with increased rate of loss of function, associated with: a. Tubular atrophy, interstitial fibrosis, fibrous intimal thickening of arteries (TA/IF/FIT) b. Activity of fibrosis and injury 3. Transplant glomerulopathy 4. Specific diseases e.g. a. Recurrent or de novo renal disease b. BK nephropathy c. Hemolytic–uremic syndrome d. Calcineurin inhibitor toxicity as a primary disease emsp;e. Diabetic nephropathy f. Hypertensive renal disease 5. Accelerating processes: factors which may accelerate progression of other diseases: e.g. a. Hypertension accelerating other disease b. Calcineurin inhibitor toxicity accelerating other diseases c. Diabetes d. Proteinuria e. Lipid abnormalities

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by loss of function, but function is not always a sensitive test for injury. Rejection is of two types: T-cell-mediated and antibody-mediated, and may occur early or late. The mechanisms of early and late rejection are not known to be different. Kidneys that lack criteria for these diagnoses do not have rejection. [Tubulitis found on protocol biopsy of a stable kidney (‘silent tubulitis’ or ‘subclinical rejection’) is not rejection by our definition if there is no documented injury, i.e. if function is stable and there is no parenchymal injury (24). The significance of silent tubulitis is the subject of ongoing studies (25)] 2. Allograft nephropathy: defined by function (reduced GFR) and pathology (criteria for nephron loss, interstitial fibrosis, and FIT in small arteries (TA/IF/FIT). (This is what the Banff classification recognizes as ‘chronic’ allograft nephropathy. However, as noted, I avoid the word ‘chronic’ because it is ambiguous.) FIT may reflect previous arterial injury, but may often be a nonspecific change linked to the parenchymal deterioration of allograft nephropathy (26). Protocol biopsies demonstrate that TA/IF/FIT is widespread – up to 60–70% of kidney grafts at 6–12 months, most of them stable (27). These lesions correlate with donor age, cold ischemic time, brain death, and drug toxicity as well as rejection. Thus we can describe parenchymal, interstitial, and arterial changes without implying either their cause or an obligatory progression. Peritubular capillary basement membrane multilayering on electron microscopy is a lesion that is being evaluated in allograft nephropathy. In its extreme form (seven layers or more), it is often seen in allografts previously damaged by severe or recurrent rejection (28). However, the extreme form is very uncommon with contemporary immunosuppression, and less severe forms (e.g. 5 layers) have uncertain significance. 3. Allograft glomerulopathy: this is an uncommon but important entity, the pathogenesis of which is unknown (29, 30). 4. Distinct diseases: such as BK nephropathy, recurrent glomerulonephritis, hemolytic uremic syndrome, and pure forms of calcineurin inhibitor toxicity and recurrent diabetes. 5. Progression factors: the presence of influences that could accelerate progression without themselves being the primary pathology, such as hypertension, proteinuria, and subtle effects of diabetes, calcineurin inhibitors, and other stresses.

Implications of the New Approach The above approach to rejection has a number of novel concepts. First, it emphasizes the central question: is the graft rejecting (deteriorating due to alloimmune injury)? Second, it eliminates ‘acute’ and ‘chronic’ in favor of descriptions such 197

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as early, late, persistent, recurrent, or refractory. The pathologist would assess the extent and activity of the inflammatory and destructive processes, and of the fibrosing and atrophic changes in the parenchyma and vessels. Third, it invites us to reassess critically the treatable components of any graft that is deteriorating. This approach emphasizes that rejection is an active diagnosis, defined by evidence of injury (e.g. deteriorating function), pathology, and where possible immunologic tests, e.g. for donor-specific alloantibody. The typical lesions of a T-cell response (interstitial inflammation, tubulitis, endothelial arteritis) or an alloantibody response are defined in the Banff schema (31). If a graft biopsy does not show these lesions, we must say it does not have rejection, pending the definition of additional lesions. Rejection is active, at least intermittently, in many biopsies from late grafts with deteriorating function. Late rejection often reflects patient noncompliance, but ineffective immunosuppression is also a factor, and the diagnosis should prompt a re-evaluation of immunosuppressive management. Some grafts with late deterioration have donorspecific anti-HLA antibody responses. Staining of the peritubular capillaries for complement product C4d has emerged as a valuable indicator of early antibody-mediated rejection (32), and is currently being evaluated for the diagnosis of late antibody-mediated rejection. There may be smoldering forms of alloimmune injury not yet defined in the Banff classification. If so, let us define them. The ‘you can’t see them but they are there’ approach should be left with folk medicine. The Banff classification is a work in progress: new criteria (pathology, immunologic tests) will be proposed, confirmed, and added to the classification. Then, they too can be called rejection. Does rejection trigger progression even after the immune response has been completely suppressed? Hunsicker’s analysis indicated that rejection depresses the 6-month GFR but does not alter the subsequent slope of the GFR (22). Nevertheless, this issue remains controversial. In renal disease, nephrons shut down as intact units regardless of the site in the nephron that is injured, probably due to a regulatory mechanism in the nephron (33). Thus loss of nephrons damaged by rejection may progress after the immune response has been successfully reversed, due to failure of repair. One proposal is that basement membrane disruption secondary to tubulitis may lead to continued late progression (34). Nephron loss is a normal event in the kidney with age, and the mechanisms of nephron loss after injury may share path-

ways with normal nephron loss due to the stresses of time. in essence, we need to learn more about homeostasis in kidney and other transplanted organs: how parenchyma and vessels sustain and repair themselves over time, and why injury exceeds the limits of repair. This approach invites a critical reassessment of arterial intimal thickening and interstitial fibrosis. FIT may be the result of arterial rejection injury but may also be due to obliteration of the capillary bed and the nephrons that the artery is supplying, in the process of allograft nephropathy. FIT is seen in small end-stage kidneys of many types (35), in the artery to an amputated limb, and in the artery to the post-partum uterus. Thus FIT may be secondary to loss (‘amputation’) of nephrons and capillary bed, rather than the reverse. FIT is the universal lesion of arterial senescence as well, and must be interpreted with caution in kidneys from old donors. Similarly, IF may not be a primary process but may simply reflect nephron loss: if so, the question is not how can we stop fibrosis but how can we stop nephron loss.

The Role of Immunologic Mechanisms in the Pathologic Lesions of Rejection A major challenge to transplant scientists is to define how lesions such as tubulitis are mediated by the immune response, and how these mechanisms lead to the lesions of allograft nephropathy. We have evidence in our own studies that T-cell mechanisms and antibody-mediated mechanisms can be distinguished by pathology (36), and that tubulitis is the major T-cell mediated lesion. Tubulitis can occur early or late, and should be regarded as rejection when function is deteriorating at any time. One key issue is whether the T cells in tubulitis lesions, early or late, are using direct recognition, i.e. are forming immunologic synapses (37) with the epithelial cells. Although some immunologists believe that ‘chronic rejection’ is a distinct type of immune process, the issue of whether different mechanisms operate in early vs. late rejection, and how these mechanisms are related to the pathology, remains uncertain. A rich literature has documented that indirect recognition is operating in many grafts with deteriorating function (38–47). But indirect mechanisms may also operate in early rejection, and may have multiple roles in allograft injury, such as delayed type hypersensitivity or help for alloantibody production. Indirect T-cell sensitization may also be a consequence of allograft injury: thus the raised frequencies of T

Table 3: Five questions to ask about a graft with deteriorating function 1. Is the graft undergoing rejection, i.e. is an alloimmune response (T cell, alloantibody) present and damaging the graft? Is this failure of the immunosuppressive prescription or failure of implementation, e.g. noncompliance, inadequate levels. 2. What is the state of the parenchyma, arteries, interstitium? Is there evidence of active fibrosis? 3. Is allograft glomerulopathy present? 4. Is a specific disease identifiable? 5. Are there accelerating factors?

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cells recognizing donor peptides in some deteriorating grafts may be an effect rather than a cause. The relationship of indirect mechanisms to alloantibody production is also complex. Because indirect recognition leads to ‘help’ for alloantibody production, one effector mechanism of indirect rejection is alloantibody-mediated rejection. In some cases alloantibody may not be pathogenic but may indicate other indirect pathway effectors, e.g. delayed type hypersensitivity. Transplantation scientists must now define the roles of both direct and indirect recognition in the lesions of T-cell mediated lesions such as tubulitis and endothelialitis; define the mechanisms that lead to antibody-mediated rejection; and explain how various mechanisms produce the different lesions of rejection.

Where Do We Go from Here? We should take a fresh unbiased view of the phenomena in the transplant population, and in model systems that closely simulate the pathology of clinical transplants. There are five questions to ask concerning any transplant with impaired function (Table 3), the answers to which should help to understand and reduce graft loss. A deteriorating graft must be approached as a solvable problem. In many cases untreated rejection may be identified, suggesting inadequate immunosuppression or noncompliance. This exercise may identify new varieties of alloimmune injury not covered within the existing Banff criteria, which can be validated and added to the schema. Perhaps microarrays and other new molecular approaches will define rejection subtypes that have evaded morphologic definition. We also need to study mechanisms of progression in organs that have sustained injury, and to define the pathogenesis of transplant glomerulopathy and its relationship to alloimmunity. A revolution is a beginning, not an end.

References 1. Kasiske BL, Heim-Duthoy KL, Tortorice KL, Rao KV. The variable nature of chronic declines in renal allograft function. Transplant 1991; 51: 330–334. 2. Hildemann WH, Walford RL. Chronic skin homograft rejection in the Syrian hamster. Ann NY Acad Sci 1960; 87: 56–77. 3. Hume DM, Merrill JP, Miller BF, Thorn GW. Experiences with renal homotransplantation in the human: report of nine cases. J Clin Invest 1955; 34: 327–382. 4. Peart WS, Rendall JM, Starzl TE et al. Human renal transplants. I. Glomerular changes. Lab Invest 1967; 16: 153–181. 5. Jeannet M, Pinn VW, Flax MH, Winn HJ, Russell PS. Humoral antibodies in renal allotransplantation in man. N Engl J Med 1970; 282: 111–117. 6. Williams GM, Lee HM, Weymouth RF et al. Studies in hyperacute and chronic renal homograft rejection in man. Surgery 1967; 62: 204– 212. 7. Harlan WR Jr, Holden KR, Williams GM, Hume DM. Proteinuria and nephrotic syndrome associated with chronic rejection of kidney transplants. N Engl J Med 1967; 277: 769–776.


8. Takemoto S, Cho YW. Significance of the donor age effect on kidney transplants. In: Cecka, JM, Terasaki, PI, eds. Clinical Transplants. Los Angeles, CA: UCLA Tissue Typing Laboratory; 1997. pp. 366–372. 9. Libby P, Pober JS. Chronic rejection. Immunity 2001; 14: 387–397. 10. Pirsch JD, Kalayoglu M, Hafez GR, D’Alessandro AM, Sollinger HW, Belzer FD. Evidence that the vanishing bile duct syndrome is vanishing. Transplant 1990; 49: 1015–1018. 11. Yousem SA, Burke CM, Billingham ME. Pathologic pulmonary alterations in long-term human heart-lung transplantation. Hum Pathol 1985; 16: 911–923. 12. Dawkins KD, Jamieson SW, Hunt SA et al. Long-term results, hemodynamics, and complications after combined heart and lung transplantation. Circulation 1985; 71: 919–926. 13. Stewart KC, Patterson GA. Current trends in lung transplantation. Am J Transplant 2001; 1: 204–210. 14. Paul LC. Chronic allograft nephropathy: an update. [Review] [142 refs]. Kidney Int 1999; 56: 783–793. 15. Ponticelli C. Progression of renal damage in chronic rejection. Kidney Int 2000; 57 (Suppl. 75): S62–S70. 16. Halloran PF, Melk A, Barth C. Rethinking chronic allograft nephropathy – the concept of accelerated senescence [review]. J Am Soc Nephrol 1999; 10: 167–181. 17. Ringers J, Rosendaal FR, Claas FH et al. Increased immunogenicity and cause of graft loss of old donor kidneys. J Am Soc Nephrol 2001; 12: 1538–1546. 18. Riera L, Fulladosa X, Ramos R et al. Donor age and delayed graft function as predictors of renal allograft survival in rejection-free patients. Nephrol Dial Transplant 1999; 14: 930–935. 19. Terasaki PI, Cecka JM, Gjertson DW, Takemoto S. High survival rates of kidney transplants from spousal and living unrelated donors. N Engl J Med 1995; 333: 333–336. 20. Halloran PF, Hunsicker LG. Delayed graft function: State of the Art. November 10–11, 2000. Summit Meeting, Scottsdale, Arizona, USA. Am J Transplant 2001; 1: 115–120. 21. Brasile L, Stubenitsky BM, Booster MH, Arenada D, Haisch C, Kootstra G. Hypothermia – a limiting factor in using warm ischemically damaged kidneys. Am J Transplant 2001; 1: 316–320. 22. Hunsicker LG, Bennett LE. Acute rejection reduces creatinine clearance (Ccr) at 6 months following renal transplantation but does not affect subsequent slope of Ccr [abstract]. Transplant 1999; 67: S83. 23. Hunsicker LG, Adler S, Caggiula A et al. Predictors of the progression of renal disease in the Modification of Diet in Renal Disease Study. Kidney Int 1997; 51: 1908–1919. 24. Matas AJ, Solez K. From first principles – tubulitis in protocol biopsies and learning from history. Am J Transplant 2001; 1: 4–5. 25. Bartosh SM, Thistlethwaite JR, Woodle ES et al. The relationship of untreated borderline infiltrates by the Banff criteria to acute rejection in renal allograft biopsies. J Am Soc Nephrol 1999; 10: 1806–1814. 26. Giordani C, Riera L, Fulladosa X et al. Serial protocol biopsies to quantify the progression of chronic transplant nephropathy in stable renal allografts. Am J Transplant 2001; 1: 82–88. 27. Solez K, Vincenti F, Filo R. Histopathologic findings from two-year protocol biopsies from a US multicenter kidney transplant trial comparing tacrolimus versus cyclosporine: a report of the FK506 Kidney Transplant Study Group. Transplant 1998; 66: 1736–1740. 28. Iva´nyi B, Fahmy H, Brown H, Szenohradszky P, Halloran PF, Solez K. Peritubular capillaries in chronic renal allograft rejection: a quantitative ultrastructural study. Hum Pathol 2000; 31: 1129–1138. 29. Fogo A. Chronic transplant glomerulopathy. Am J Kidney Dis 2000; 35: E28. 30. Suri DL, Tomlanovich SJ, Olson JL, Meyer TW. Transplant glomerulopathy as a cause of late graft loss. Am J Kidney Dis 2000; 35: 674– 680. 31. Racusen LC, Solez K, Colvin RB et al. The Banff 97 working classification of renal allograft pathology. Kidney Int 1999; 55: 713–723.

199

Halloran 32. Collins AB, Schneeberger EE, Pascual MA et al. Complement activation in acute humoral renal allograft rejection: diagnostic significance of C4d deposits in peritubular capillaries. J Am Soc Nephrol 1999; 10: 2208–2214. 33. Bricker NS, Morrin PAF, Kime SW Jr. The pathologic physiology of chronic Bright’s disease. An exposition of the ‘intact nephron hypothesis’. J Am Soc Nephrol 1997; 8: 1470–1476. 34. Bonsib SM. Acute rejection-associated tubular basement membrane defects and chronic allograft nephropathy. Kidney Int 2000; 58: 2206–2214. 35. Nishi T, Bond C Jr, Brown G, Solez K, Heptinstall RH. A morphometric study of arterial intimal thickening in kidneys of dialyzed patients. Am J Pathol 1979; 95: 597–610. 36. Trpkov K, Campbell P, Pazderka F, Cockfield S, Solez K, Halloran PF. Pathologic features of acute renal allograft rejection associated with donor-specific antibody. Transplant 1996; 61: 1586–1592. 37. Bromley SK, Burack WR, Johnson KG et al. The immunological synapse. Annu Rev Immunol 2001; 19: 375–396. 38. Baker RJ, Hernandez-Fuentes MP, Brookes PA, Chaudhry AN, Cook HT, Lechler RI. Loss of direct and maintenance of indirect alloresponses in renal allograft recipients: implications for the pathogenesis of chronic allograft nephropathy. J Immunol 2001; 167: 7199–7206. 39. SivaSai KS, Smith MA, Poindexter NJ et al. Indirect recognition of donor HLA class I peptides in lung transplant recipients with bronchiolitis obliterans syndrome. Transplant 1999; 67: 1094–1098. 40. Jaramillo A, Smith MA, Phelan D et al. Development of ELISA-detected anti-HLA antibodies precedes the development of bronchiolitis

200

41.

42.

43.

44.

45.

46.

47.

obliterans syndrome and correlates with progressive decline in pulmonary function after lung transplantation. Transplant 1999; 67: 1155–1161. Vella JP, Spadafora-Ferreira M, Murphy B et al. Indirect allorecognition of major histocompatibility complex allopeptides in human renal transplant recipients with chronic graft dysfunction. Transplant 1997; 64: 795–800. Vella JP, Vos L, Carpenter CB, Sayegh MH. Role of indirect allorecognition in experimental late acute rejection. Transplant 1997; 64: 1823– 1828. Liu Z, Colovai AI, Tugulea S et al. Indirect recognition of donor HLADR peptides in organ allograft rejection. J Clin Invest 1996; 98: 1150– 1157. Molajoni ER, Cinti P, Orlandini A et al. Mechanism of liver allograft rejection: the indirect recognition pathway. Hum Immunol 1997; 53: 57–63. Ciubotariu R, Liu Z, Colovai AI et al. Persistent allopeptide reactivity and epitope spreading in chronic rejection of organ allografts. J Clin Invest 1998; 101: 398–405. Hornick PI, Mason PD, Baker RJ et al. Significant frequencies of T cells with indirect anti-donor specificity in heart graft recipients with chronic rejection. Circulation 2000; 101: 2405–2410. Hornick PI, Mason PD, Yacoub MH, Rose ML, Batchelor R, Lechler RI. Assessment of the contribution that direct allorecognition makes to the progression of chronic cardiac transplant rejection in humans. Circulation 1998; 97: 1257–1263.
