INTRODUCTION

CLINICAL PRESENTATION

Standard liver injury tests abnormalities in a patient with CR usually show a progressive cholestatic pattern, with preferential elevation of gamma-glutamyl transpeptidase and alkaline phosphatase(6, 14, 15). The same pattern of liver injury test elevation can be seen with obstructive cholangiopathy and with cholestatic hepatitis(14). Therefore, cholangiography may be required in some cases to distinguish between CR and biliary obstruction, particularly since the latter can also cause small bile duct loss at the periphery of the liver. Findings in a core needle biopsy can easily distinguish between a cholestatic hepatitis and CR. The diagnosis of CR can also be supported by selective hepatic angiography, which shows pruning of the intrahepatic arteries with poor peripheral filling and segmental narrowing (6, 16-18).

RISK FACTORS

HISTOPATHOLOGICAL FEATURES AND PATHOPHYSIOLOGY OF CHRONIC LIVER ALLOGRAFT REJECTION

As already mentioned, the diagnosis of CR is clinically suspected from the signs and symptoms listed above, and confirmed histopathologically, by recognizing the two principal features: obliterative arteriopathy (OA) , and severe damage and loss of small (< 60 microns) bile ducts (2, 3, 6, 7, 9-13, 38). Cases with either isolated bile duct loss or foam cell arteriopathy alone may occur, but usually both features are found together(13, 39). Unfortunately, arteries with pathognomonic changes are rarely present in needle biopsy specimens, and therefore what has been observed about OA in the liver has come from examination of failed allografts removed at the time of re-transplantation. Therefore, in biopsy specimens, significant weight is usually placed on damage and loss of small bile ducts, but ductopenia can be non-specific finding that occasionally occurs as a result of non-rejection-related complications(5, 15).

Until recently, the most widely used criteria defined CR as bile duct loss in more than 50% of the portal tracts (6, 13, 22, 23). However, an inter-institutional study recently showed that CR could be reliably identified in needle biopsy specimens on the basis of widespread biliary epithelial cell atrophy and pyknosis(15), with or without bile duct loss. Currently, in a biopsy specimen, the minimal diagnostic criteria for CR are a) the presence of bile duct atrophy/pyknosis, affecting a majority of the bile ducts, with or without bile duct loss; or b) convincing foam cell obliterative arteriopathy; or c) bile duct loss affecting greater than 50% of the portal tracts(2, 4-6, 9, 10, 15, 16, 22, 40, 41).

Bile duct loss is recognized by the presence of hepatic artery branches without accompanying bile ducts, or by the absence of both ducts and hepatic artery branches(6). The prevalence of bile duct loss is determined by calculating the ratio between the number of hepatic artery branches and the number of bile ducts within a portal tract. Normally, this ratio is greater than 0.7(11, 42, 43). The greater the number of portal tracts counted, the more likely the count is to be valid. Sometimes this will require the evaluation of several sequential biopsies. Recognition of portal tracts may be difficult in cases where the hepatic arterioles have also been destroyed(11, 38, 44). In such cases, reliance on other architectural landmarks, such as cholestasis, which is centrilobular predominant in CR can be helpful.

The early, potentially reversible, stage of CR is identified primarily by degenerative changes of the biliary epithelium, even before overt duct loss is detected. These include uneven spacing of individual epithelial cells , eosinophilic transformation of the cytoplasm , similar to that observed in primary biliary cirrhosis, and ducts only partially lined by epithelial cells. Portal inflammation is usually mild and ductulocentric, and consists of CD3+CD4+, and CD3+CD4- T cells, CD20+ B cells and CD68+ macrophages and plasma cells(45, 46). The presence of CD2+/CD8+ T-lymphocytes in contact with the degenerating biliary epithelial cells(47) and increased transcripts for TH1-type cytokines IL-2 and gamma-interferon, and the presence of granzyme B, indicate that cytotoxic effector cells are at least partially responsible for biliary epithelial cell damage (35, 45). However, TUNEL assays suggest that apoptosis is not a common pathway in the biliary epithelial cell damage(48).

As the disorder progresses, bile ducts loss affects a greater percentage of the portal tracts and biliary epithelial cells become difficult to identify. Special stains (e.g. trichrome, PAS-D, cytokeratin ) may be used to enhance their detection by highlighting the basement membrane or selectively staining the biliary epithelial cells, but generally the special stains are not needed(49). The smaller the duct, the more susceptible to damage and loss(11, 38). In most instances, bile duct loss is verified the presence of a portal tract containing a hepatic artery branch, without an accompanying bile duct, , which should be present within a distance of three times the shortest diameter of the artery in > 80% of portal tracts(11, 38, 42, 43). In very advanced cases, there is complete destruction of the small arterioles, peribiliary plexus (11, 38, 44) and the bile ducts, which results in a "scarred" appearance of the portal tract connective tissue.

Bile duct damage is caused by a combination of direct immunological damage as described above, combined with ductal ischemia because of destruction of the portal tract microvasculature and obliterative arteriopathy, and possibly interference with lymphatic drainage(11, 38, 44, 50). There are several possible non-exclusionary explanations for the preferential destruction of bile ducts: 1) the presence of a basement membrane, which could potentially play a role in migration, positioning and co-stimulation of T-cells; 2) an immunologically active antigenic profile of the biliary epithelial cells that is significantly different than other parenchymal cells, including class I and II MHC, and various adhesion and co-stimulatory molecules; and 3) the presence of nearby antigen presenting cells and lymphatics, that facilitate the functional role of these conduits in processing environmental antigen for local presentation and traffic to the regional lymph nodes. Thus, a ductulocentric immune response might be precipitated by environmental or autoantigens in an allograft, which creates inflammatory microenvironment, which has the potential to trigger a rejection reaction. Either reaction can compromise the structural integrity of the duct, and focally destroy the local microvasculature and lymphatic drainage, which in turn can ischemically damage the conduit and inhibit efficient antigen clearing. One could easily appreciate how this could lead to a vicious cycle, alternating between a persistent and inadequate response to environmental antigens/infections and allogeneic injury, resulting in a downward spiral of allograft structural integrity and function(51).

Despite the destruction of the bile ducts a ductular reaction (52-55) at the interface zone is unusual in CR. This might account for the observation that a well-developed cirrhosis from CR is unusual, although there are some case reports and descriptions to the contrary(33). More often, the fibrosis that develops in CR is preferentially detected in a perivenular distribution, which can result in central-to-central bridging fibrosis.

Foam cell arteriopathy can rarely be confirmed by a core needle biopsy, therefore, other "surrogate" features are often used to suggest the presence of obliterative arteriopathy. Features that suggest but do not prove the presence of foam cell arteriopathy include loss of arterioles and small arteries(< 20 microns) in > 20% of the portal tracts, centrilobular hepatocellular swelling, perivenular sclerosis, and centrilobular hepatocyte dropout.

Lobular changes commonly seen in CR include centrilobular hepatocanalicular cholestasis , intra-sinusoidal foam cell clusters , mild spotty acidophilic necrosis of hepatocytes, centrilobular hepatocyte atrophy and/or ballooning and perivenular sclerosis . Clusters of foamy macrophages are commonly seen in the sinusoids, although their presence may simply represent a non-specific response to cholestasis. The centrilobular degeneration and perivenular sclerosis may be related to either ischemia or damage from repeated bouts of "central venulitis" during acute rejection.

The diagnosis of CR is easier to establish in an explanted failed allograft. The presence of significant foam cell obliterative arteriopathy (OA) should be seen in at least some of the muscular arteries in the hilum. Arteries affected by OA show endothelial hypertrophy and luminal narrowing most commonly because of subintimal deposition of lipid-laden cells that are transformed macrophages and intimal and medial myocytes. Foamy macrophages can also be seen around bile ducts and veins in the connective tissue. Lymphohistiocytic intimal inflammation, smooth muscle cell proliferation, disruption of the elastic lamina, and periadventitial and intra-medial inflammation of medium-sized arteries may also be present. Occasionally, there is superimposed arterial thrombosis. Major hilar bile ducts may show sloughing of the epithelium, focal necrosis, intraluminal papillary hyperplasia of the epithelium, mural fibrosis and acute and chronic inflammation.

STAGING OF CHRONIC LIVER ALLOGRAFT REJECTION

Most, if not all, patients who develop CR will experience one, or often more, episodes of acute rejection. In fact, CR evolves directly from inadequately controlled acute rejection episodes in up to 60% of patients who develop CR(2, 22, 23, 41). In the remaining patients, CR can develop more indolently, but even these have a documented history of acute rejection episodes. The transition from acute to the early stage of CR is accompanied by biliary epithelial cell atrophy/pyknosis involving a majority of the bile ducts, as described and illustrated above, and with or without bile duct loss in < 50 % of the portal tracts. Perivenular necrosis, hepatocellular swelling and hepatocanalicular cholestasis may be seen in the centrilobular regions, but perivenular fibrosis is not severe (bridging) and foam cell clusters are usually absent. Late CR is defined by bile duct loss involving 50 % or more of the portal tracts. Atrophy/pyknosis are usually seen in any remaining bile ducts and moderate tosevere perivenular fibrosis and foam cell clusters are present. The perivenular fibrosis is associated with an increase of extracellular matrix proteins fibronectin, tenascin, undulin, and collagen VI and an accumulation of alpha-actin-positive cells and TGF-b1-expressing macrophages (56). Severe obliterative arteriopathy is also present, but this is usually not detectable in needle biopsies taken from the periphery. The development of cirrhosis is unusual in our experience.

Several recent studies have chronicled the sequential changes associated with the development of CR and clinicopathological changes associated with either progression to allograft failure or recovery to normal or near normal liver injury tests and/or liver architecture (15, 41). Using strict clinical and histopathological criteria, which included the absence of biliary strictures or obstruction and other co-morbid conditions that might cause ductopenia, a cohort of 23/916 patients from the National Institute of Diabetes and Digestive and Kidney Diseases Liver Transplant Database developed CR. Of these, 13 went on to graft failure from CR, whereas 10 recovered to normal or near normal liver injury tests and liver architecture. In 14 of these patients, CR evolved directly from acute rejection, as described above. In the remaining patients, CR evolved from the early to late phases over a period of time from a few days to a year (41). In contrast, recovery occurred over a period of time from several months to more than one year.

Histopathological findings associated with progression to allograft failure included bile duct loss in more than 50 % of the portal tracts, severe (bridging) perivenular fibrosis and foam cell clusters within the sinusoids (41). It should be noted however, that the histopathological features associated with progression to allograft failure or recovery overlapped, and there was no specific finding alone, which reliably predicted the outcome. More specifically, some patients with > 50 % bile duct loss recovered, whereas other patients with < 50 % bile duct loss went on to allograft failure.

In those who recovered, a "ductular reaction" at the interface zone has been described before and during clinical improvement (2, 3, 41). Whether the recovery of ducts is related to proliferation of residual ductal epithelium, maturation of liver progenitor cells, or metaplasia of periportal hepatocytes, is an intriguing question about liver growth and development.

FASCINATING ASPECTS OF CHRONIC LIVER ALLOGRAFT REJECTION

Resistance of liver allografts to CR can best be explained by the immunological theories of so called "hepatic tolerogenecity". They can be broadly separated into two general categories, based on whether emphasis is placed on the parenchymal or non-parenchymal portion of the liver, which in turn, results in: 1) deletion or 2) functional anergy in the responding T cell repertoire. Release of soluble donor MHC class I antigen from the allograft, supporting the importance of the parenchyma, cannot account for these observations, alone (57). Murine liver allografts are routinely accepted between strains of mice that show no difference between the class I loci, but are mismatched for class II (58). In addition, fully allogeneic liver allografts from class I or II MHC deficient mice, which do not shed soluble MHC antigens (58, 59), are also accepted without immunosuppression. Moreover, other organs also secrete soluble MHC antigens (60) but they are routinely rejected, and infusion of exogenous soluble MHC usually leads to only slight graft prolongation.

One potential explanation for the importance of the parenchyma relies on the concept that allogeneic hepatocytes provide only one of two signals needed for allogeneic lymphocyte activation (61). Lack of important co-stimulatory molecules is thought to result in the induction of anergy in the responding lymphocyte populations (61). However, when transgenic mice that aberrantly express the allogeneic MHC class I molecule H-2Kb (Kb) in the liver, using a metallothionein promoter (62), are crossed with a strain that develops CD8+ T cells specific for the Kb molecule, lymphocyte-mediated "autoimmune" liver damage can be induced under certain conditions. Interestingly, most of the CD8+ cells responsive to Kb were eliminated by the intense intrahepatic activation, but some of the liver continued to show chronic low grade inflammation (62). However, great care had to be taken to assure that alloantigen expression was limited to the liver (62). Interpretation of these complicated experiments is difficult, but it appears that the liver may be able to effect an activation-induced partial clonal deletion of allogeneic lymphocytes (62), as originally proposed by Kamada (63). This may represent a special circumstance, because alloantigen expression on other non-hematolymphoid cells such as pancreatic islets, does not lead to anergy (64), but to immunological "ignorance" (65), which is an important difference. Induction of true anergy may in fact, require presentation of antigen by professional antigen presenting cells.

It has been our contention that so called "hepatic tolerogenecity" is in large part, a result of hematolymphoid microchimerism (66-69) sustained by donor hematopoietic stem contained within the liver (70-72). The immunologic mechanisms involved in graft acceptance appear to be a non-deletional, active process that that requires donor antigen presenting cells(73). The details of the role of donor hematopoietic cells in organ allograft acceptance are described in detail elsewhere(73, 74).

DIFFERENTIAL DIAGNOSIS

The first problem area, distinguishing early CR from a normal or near normal biopsy, can be minimized by paying close attention to liver injury tests and correlating them with the histopathological findings. Selective elevation of the "canalicular" enzymes, alkaline phosphatase and gamma glutamyl transpeptidase (ALP, GGTP), in an otherwise healthy long term liver allograft survivor should prompt the pathologist to look more closely at the integrity of the bile ducts and the number of portal tract sampled. If there are less than 6 - 8 portal tracts sampled, and there is no other explanation for the elevated GGTP and ALP, re-biopsy should be suggested. Conversely, widespread bile duct atrophy/pyknosis or bile duct loss without a significant (> 4X normal) elevation of ALP or GGTP is unusual, although it does happen on occasion(15).

The second problem area, distinguishing CR from chronic hepatitis is more difficult to resolve. Three separate issues contribute to this difficulty(15): 1) focal bile duct damage is often seen in chronic viral and autoimmune hepatitis; 2) "parenchymal-type" rejection, as originally proposed by Kemnitz et al(33), might be histopathologically indistinguishable from CR; and 3) CR and chronic hepatitis can co-exist(15). The first issue can be minimized by strict adherence to histopathological criteria. In chronic viral or autoimmune hepatitis, bile duct damage is limited to an occasional duct and rarely, if ever, results in significant bile duct loss. In contrast, small bile duct damage in CR involves a majority of the bile ducts, and is accompanied by atrophic changes in the biliary epithelium. It also frequently leads to bile duct loss. Conversely, interface activity accompanied by a type II ductular reaction is more common with chronic hepatitis than in CR. The second issue is more difficult to resolve and is currently the focus of several studies. Resolution of this problem will require long-term follow-up and close clinical correlation. However, it is somewhat reassuring that most large liver transplant programs are not reporting an increased incidence of unexplained cirrhosis in long term survivors, which might be expected from this type of rejection(14, 75). Lastly, the co-existence of chronic hepatitis and rejection is expected, since allograft inflammation induced by recurrent viral disease is associated with increased cytokines, which in turn, can up-regulate adhesion and major histocompatibility molecules involved in precipitating a rejection reaction. The key to identifying cases with both chronic hepatitis and CR is recognizing the features of hepatitis, along with bile duct damage that is more prevalent and severe than would be expected for chronic hepatitis alone.

Lastly, there are many potential causes of non-rejection-related ductopenia without arteriopathy in liver allograft recipients, as in the general population. One of the most common causes in an allograft is chronic obstructive cholangiopathy since bile duct obstruction and stricturing are relatively common long term complications, affecting from 10 - 20 % of long term survivors (14, 75). Adverse drug reaction, cytomegalovirus infection (30, 32, 76, 77) and arterial compromise are other, less common causes. Likewise, there are several causes of perivenular fibrosis, such as outflow obstruction and veno-occlusive disease because of adverse drug reactions. Again however, review of previous biopsies and clinical correlation will help to distinguish between these possibilities.

Typical examples of CR seen in consultation:

Failed liver allograft

Needle biopsy with CR

REFERENCES

1. Demetris, A.J., Murase, N., Lee, R.G., Randhawa, P., Zeevi, A., et al. Chronic rejection. A general overview of histopathology and pathophysiology with emphasis on liver, heart and intestinal allografts. Ann Transplant 1997;2(2):27-44.

2. Freese, D.K., Snover, D.C., Sharp, H.L., Gross, C.R., Savick, S.K., et al. Chronic rejection after liver transplantation: a study of clinical, histopathological and immunological features. Hepatology 1991;13(5):882-91.

3. Hubscher, S.G., Buckels, J.A., Elias, E., McMaster, P., Neuberger, J. Vanishing bile-duct syndrome following liver transplantation--is it reversible? Transplantation 1991;51(5):1004-10.

4. Demetris, A.J., Fung, J.J., Todo, S., McCauley, J., Jain, A., et al. FK 506 used as rescue therapy for human liver allograft recipients. Transplant Proc 1991;23(6):3005-6.

5. Demetris, A.J., Fung, J.J., Todo, S., McCauley, J., Jain, A., et al. Conversion of liver allograft recipients from cyclosporine to FK506 immunosuppressive therapy--a clinicopathologic study of 96 patients. Transplantation 1992;53(5):1056-62.

6. Anonymous. - Terminology for hepatic allograft rejection. International Working Party. [Review]. Hepatology 1995;22(2):648-54.

7. Fennell, R.H., Jr. Ductular damage in liver transplant rejection: its similarity to that of primary biliary cirrhosis and graft-versus-host disease. Pathol Annu 1981;16(Pt 2):289-94.

8. Vierling, J.M., Fennell, R.H., Jr. Histopathology of early and late human hepatic allograft rejection: evidence of progressive destruction of interlobular bile ducts. Hepatology 1985;5(6):1076-82.

9. Grond, J., Gouw, A.S., Poppema, S., Sloof, M.J.H., Gips, C.H. Chronic rejection in liver transplants: a histopathologic analysis of failed grafts and antecedent serial biopsies. Transplantation Proceedings 1986;18:128-135.

10. Ludwig, J., Wiesner, R.H., Batts, K.P., Perkins, J.D., Krom, R.A. The acute vanishing bile duct syndrome (acute irreversible rejection) after orthotopic liver transplantation. Hepatology 1987;7(3):476-83.

11. Oguma, S., Belle, S., Starzl, T.E., Demetris, A.J. A histometric analysis of chronically rejected human liver allografts: insights into the mechanisms of bile duct loss: direct immunologic and ischemic factors. Hepatology 1989;9(2):204-9.

12. Portmann, B., Neuberger, J., Williams, R. Intrahepatic bile duct lesions. In: Calne RY, ed. Liver Transplantation. the Cambridge-Kings College Hospital Experience. London: Grune & Stratton, 1983:279.

13. Wight, D.A. - Chronic liver transplant rejection: definition and diagnosis. Transplantation Proceedings 1996;28(1):465-7.

14. Pappo, O., Ramos, H., Starzl, T.E., Fung, J.J., Demetris, A.J. Structural integrity and identification of causes of liver allograft dysfunction occurring more than 5 years after transplantation. Am J Surg Pathol 1995;19(2):192-206.

15. Demetris, A.J., Seaberg, E.C., Batts, K.P., Ferrell, L., Lee, R.G., et al. Chronic liver allograft rejection: a National Institute of Diabetes and Digestive and Kidney Diseases interinstitutional study analyzing the reliability of current criteria and proposal of an expanded definition. National Institute of Diabetes and Digestive and Kidney Diseases Liver Transplantation Database. Am J Surg Pathol 1998;22(1):28-39.

16. Lowes, J.R., Hubscher, S.G., Neuberger, J.M. Chronic rejection of the liver allograft. Gastroenterol Clin North Am 1993;22(2):401-20.

17. White, R.M., Zajko, A.B., Demetris, A.J., Bron, K.M., Dekker, A., et al. Liver transplant rejection: angiographic findings in 35 patients. American Journal of Roentgenology 1987;148(6):1095-8.

18. Devlin, J., Page, A.C., O'Grady, J., Portmann, B., Karani, J., et al. Angiographically determined arteriopathy in liver graft dysfunction and survival. J Hepatol 1993;18(1):68-73.

19. Candinas, D., Gunson, B.K., Nightingale, P., Hubscher, S., McMaster, P., et al. Sex mismatch as a risk factor for chronic rejection of liver allografts. Lancet 1995;346(8983):1117-21.

20. Farges, O., Nocci Kalil, A., Sebagh, M., Reynes, M., Bismuth, H. Low incidence of chronic rejection in patients experiencing histological acute rejection without simultaneous impairment in liver function tests. Transplant Proc 1995;27(1):1142-3.

21. Hayashi, M., Keeffe, E.B., Krams, S.M., Martinez, O.M., Ojogho, O.N., et al. Allograft rejection after liver transplantation for autoimmune liver diseases [see comments]. Liver Transpl Surg 1998;4(3):208-14.

22. Wiesner, R.H., Ludwig, J., van Hoek, B., Krom, R.A. Current concepts in cell-mediated hepatic allograft rejection leading to ductopenia and liver failure. Hepatology 1991;14(4 Pt 1):721-9.

23. Wiesner, R.H., Ludwig, J., Van Hoek, B., Krom, R.A.F. Chronic Hepatic Allograft Rejection: a review of ductopenic rejection and the vanishing bile duct syndrome. In: Paul LC, Solez K, eds. Organ Transplantation: long-term results. New York, N.Y.: Marcel Dekker, 1992:197-216.

24. Group, E.F.M.L.S. Randomised trial comparing tacrolimus (FK506) and cyclosporin in prevention of liver allograft rejection. European FK506 Multicentre Liver Study Group [see comments]. Lancet 1994;344(8920):423-8.

25. Devlin, J.J., O'Grady, J.G., Tan, K.C., Calne, R.Y., Williams, R. Ethnic variations in patient and graft survival after liver transplantation. Identification of a new risk factor for chronic allograft rejection. Transplantation 1993;56(6):1381-4.

26. Batts, K. Liver allograft rejection: current status of classification and grading. Transplant Proc 1996;28(1):453-6.

27. Donaldson, P., Underhill, J., Doherty, D., Hayllar, K., Calne, R., et al. Influence of human leukocyte antigen matching on liver allograft survival and rejection: "the dualistic effect". Hepatology 1993;17(6):1008-15.

28. Donaldson, P.T., Thomson, L.J., Heads, A., Underhill, J.A., Vaughan, R.W., et al. IgG donor-specific crossmatches are not associated with graft rejection or poor graft survival after liver transplantation. An assessment by cytotoxicity and flow cytometry. Transplantation 1995;60(9):1016-23.

29. Donaldson, P.T., Alexander, G.J., O'Grady, J., Neuberger, J., Portmann, B., et al. Evidence for an immune response to HLA class I antigens in the vanishing-bileduct syndrome after liver transplantation. Lancet 1987;1(8539):945-51.

30. Manez, R., White, L.T., Linden, P., Kusne, S., Martin, M., et al. The influence of HLA matching on cytomegalovirus hepatitis and chronic rejection after liver transplantation. Transplantation 1993;55(5):1067-71.

31. Paya, C.V., Wiesner, R.H., Hermans, P.E., Larson-Keller, J.J., Ilstrup, D.M., et al. Lack of association between cytomegalovirus infection, HLA matching and the vanishing bile duct syndrome after liver transplantation. Hepatology 1992;16(1):66-70.

32. Lautenschlager, I., Hockerstedt, K., Jalanko, H., Loginov, R., Salmela, K., et al. Persistent cytomegalovirus in liver allografts with chronic rejection. Hepatology 1997;25(1):190-4.

33. Kemnitz, J., Gubernatis, G., Bunzendahl, H., Ringe, B., Pichlmayr, R., et al. Criteria for the histopathological classification of liver allograft rejection and their clinical relevance. Transplant Proc 1989;21(1 Pt 2):2208-10.

34. Demetris, A., Qian, S., H Sun, e.a. Early events in liver allograft rejection: delineation of sites of simultaneous intragraft and recipient lymphoid tissue sensitization. American Journal of Pathology 1991:138:609.

35. Fennell, R.H., Jr., Vierling, J.M. Electron microscopy of rejected human liver allografts. Hepatology 1985;5(6):1083-7.

36. Porter, K.A. Pathology of the orthotopic homograft and heterograft. In: Starzl TE, ed. Experience in Hepatic Transplantation. Philadelphia: W.B. Saunders, 1969:

37. Snover, D.C., Freese, D.K., Sharp, H.L., Bloomer, J.R., Najarian, J.S., et al. Liver allograft rejection. An analysis of the use of biopsy in determining outcome of rejection. Am J Surg Pathol 1987;11(1):1-10.

38. Oguma, S., Zerbe, T., Banner, B., Belle, S., Starzl, T.E., et al. Chronic liver allograft rejection and obliterative arteriopathy: possible pathogenic mechanisms. Transplant Proc 1989;21(1 Pt 2):2203-7.

39. Deligeorgi-Politi, H., Wight, D.G., Calne, R.Y., White, D.G. - Chronic rejection of liver transplants revisited [published erratum appears in Transpl Int 1995;8(2):163]. Transplant International 1994;7(6):442-7.

40. Adams, D.H., Hubscher, S.G., Shaw, J., Rothlein, R., Neuberger, J.M. Intercellular adhesion molecule 1 on liver allografts during rejection. Lancet 1989;2(8672):1122-5.

41. Blakolmer, K., Seaberg, E.C., Batts, K., Ferrell, L., Markin, R., et al. Analysis of the reversibility of chronic liver allograft rejection- implications for a staging system. American Journal of Surgical Pathology 1999;(in press).

42. Nakanuma, Y., Ohta, G. Histometric and serial section observations of the intrahepatic bile ducts in primary biliary cirrhosis. Gastroenterology 1979;76:1326-1332.

43. Crawford, A.R., Lin, X.Z., Crawford, J.M. The normal adult human liver biopsy: a quantitative reference standard. Hepatology 1998;28(2):323-31.

44. Matsumoto, Y., McCaughan, G.W., Painter, D.M., Bishop, G.A. Evidence that portal tract microvascular destruction precedes bile duct loss in human liver allograft rejection. Transplantation 1993;56(1):69-75.

45. Hayashi, M., Martinez, O.M., Garcia-Kennedy, R., So, S., Esquivel, C.O., et al. Expression of cytokines and immune mediators during chronic liver allograft rejection. Transplantation 1995;60(12):1533-8.

46. Demetris, A.J., Lasky, S., Van Thiel, D.H., Starzl, T.E., Whiteside, T. Induction of DR/IA antigens in human liver allografts. An immunocytochemical and clinicopathologic analysis of twenty failed grafts. Transplantation 1985;40(5):504-9.

47. McCaughan, G.W., Davies, J.S., Waugh, J.A., Bishop, G.A., Hall, B.M., et al. A quantitative analysis of T lymphocyte populations in human liver allografts undergoing rejection: the use of monoclonal antibodies and double immunolabeling. Hepatology 1990;12(6):1305-13.

48. Afford, S.C., Hubscher, S., Strain, A.J., Adams, D.H., Neuberger, J.M. Apoptosis in the human liver during allograft rejection and end-stage liver disease. J Pathol 1995;176(4):373-80.

49. Harrison, R.F., Patsiaoura, K., Hubscher, S.G. Cytokeratin immunostaining for detection of biliary epithelium: its use in counting bile ducts in cases of liver allograft rejection. J Clin Pathol 1994;47(4):303-8.

50. Demetris, A.J., Murase, N., Ye, Q., Galvao, F.H., Richert, C., et al. Analysis of chronic rejection and obliterative arteriopathy. Possible contributions of donor antigen-presenting cells and lymphatic disruption. Am J Pathol 1997;150(2):563-78.

51. Demetris, A.J., Murase, N., Starzl, T.E., Fung, J.J. Pathology of Chronic Rejection: an overview of common findings and observations about pathogenic mechanisms and possible prevention. Graft 1998;1:52- 59.

52. Popper, H. The relation of mesenchymal cell products to hepatic epithelial systems. [Review]. Progress in Liver Diseases 1990;9:27-38.

53. Popper, H., Kent, G., Stein, R. Ductular cell reaction in the liver in hepatic injury. J Mt. Sinai Hosp 1957;24:551-556.

54. Demetris, A.J., Sakamoto, T., Liu, Z., Yokomuro, S., Ezure, T., et al. The Ductular Reaction in Liver Disease emphasis on a type I response. In: Fleig WE, ed. Normal and Malignant Liver Cell Growth. Dordecht: Kluwer Academic Publishers, 1999:141-155.

55. Burt, A.D., MacSween, R.N. Bile duct proliferation--its true significance?. [Review]. Histopathology 1993;23(6):599-602.

56. Demirci, G., Nashan, B., Pichlmayr, R. - Fibrosis in chronic rejection of human liver allografts: expression patterns of transforming growth factor-TGFbeta1 and TGF-beta3. Transplantation 1996;62(12):1776-83.

57. Davies, H.S., Pollard, S.G., Calne, R.Y. Soluble HLA antigens in the circulation of liver graft recipients. Transplantation 1989;47:524-527.

58. Qian, S., Sun, H., Demetris, A.J., Fu, F., Starzl, T.E., et al. Liver graft induced donor specific unresponsiveness without class I and/or class II antigen differences. Transplantation Proceedings 1993;25(1 Pt 1):362-3.

59. Qian, S., Demetris, A.J., Murase, N., Rao, A.S., Fung, J.J., et al. Murine liver allograft transplantation: tolerance and donor cell chimerism. Hepatology 1994;19:916-924.

60. Rhynes, V.K., McDonald, J.C., Gelder, F.B., Aultman, D.F., Hayes, J.M., et al. Soluble HLA class I in the serum of transplant recipients. Annals of Surgery 1993;217(5):485-9.

61. Matzinger, P. Tolerance, danger, and the extended family. Annual Review of Immunology 1994;12:991-1045.

62. Bertolino, P., Heath, W.R., Hardy, C.L., Morahan, G., Miller, J.F. - Peripheral deletion of autoreactive CD8+ T cells in transgenic mice expressing H-2Kb in the liver. European Journal of Immunology 1995;25(7):1932-42.

63. Kamada, N. The immunology of experimental liver transplantation in the rat. Immunology 1985;55:369-389.

64. Slattery, R.M., Miller, J.F., Heath, W.R., Charlton, B. - Failure of a protective major histocompatibility complex class II molecule to delete autoreactive T cells in autoimmune diabetes. Proceedings of the National Academy of Sciences of the United States of America 1993;90(22):10808-10.

65. Miller, J.F., Heath, W.R. - Self-ignorance in the peripheral T-cell pool. [Review]. Immunological Reviews 1993;133:131-50.

66. Starzl, T.E., Demetris, A.J., Murase, N., Ildstad, S., Ricordi, C., et al. Cell migration, chimerism, and graft acceptance [see comments]. [Review]. Lancet 1992;339(8809):1579-82.

67. Starzl, T.E., Demetris, A.J., Murase, N., Thomson, A.W., Trucco, M., et al. Donor cell chimerism permitted by immunosuppressive drugs: a new view of organ transplantation. [Review]. Trends in Pharmacological Sciences 1993;14(5):217-23.

68. Starzl, T.E., Demetris, A.J., Trucco, M., Murase, N., Ricordi, C., et al. Cell migration and chimerism after whole-organ transplantation: the basis of graft acceptance [see comments]. [Review]. Hepatology 1993;17(6):1127-52.

69. Starzl, T.E., Demetris, A.J. Transplantation Milestones: viewed with one- and two-way paradigms of tolerance. JAMA 1995;273:876-879.

70. Murase, N., Starzl, T.E., Ye, Q., Tsamandas, A., Thomson, A.W., et al. Multilineage hematopoietic reconstitution of supralethally irradiated rats by syngeneic whole organ transplantation: with particular reference to the liver. Transplantation 1996;61:1-4.

71. Hays, E.F., Hays, D.M., Golde, D.W. Hematopoietic stem cells in mouse liver. Exp Hematol 1978;6:18.

72. Taniguchi, H., Toyoshima, T., Fukao, K., Nakauchi, H. Presence of hematopoietic stem cells in the adult liver. Nature Medicine 1996;2:198-203.

73. Demetris, A.J., Murase, N., Rao, A.S., Starzl, T.E. The role of passenger leukocytes in rejection and "tolerance" after solid organ transplantation: a potential explanation of a paradox. Rejection and Tolerance. J. L. Touraine et al. ed. Netherlands: Kluwer Academic Publishers, 1994:325-392.

74. Demetris, A.J., Murase, N., Fung, J.J., Starzl, T.E. Dendritic Cells in Rejection of Solid Organ Allografts. In: Lotze MT, Thomsom AW, eds. Dendritic Cells. San Diego, CA: Academic Press, 1999:339-360.

75. Slapak, G.I., Saxena, R., Portmann, B., Gane, E., Devlin, J., et al. Graft and systemic disease in long-term survivors of liver transplantation. Hepatology 1997;25(1):195-202.

76. Martelius, T., Krogerus, L., Hockerstedt, K., Bruggeman, C., Lautenschlager, I. Cytomegalovirus infection is associated with increased inflammation and severe bile duct damage in rat liver allografts. Hepatology 1998;27(4):996-1002.

77. O'Grady, J.G., Alexander, G.J., Sutherland, S., Donaldson, P.T., Harvey, F., et al. Cytomegalovirus infection and donor/recipient HLA antigens: interdependent co-factors in pathogenesis of vanishing bile-duct syndrome after liver transplantation. Lancet 1988;2(8606):302-5.

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