Diagnosis of acute rejection in liver transplantation

Seeking beyond rejection: an update on the differential diagnosis and a practical approach to liver allograft biopsy interpretation

Pathologic evaluation of liver allograft biopsies plays an integral role in the management of patients after liver transplantation. This review summarizes the clinical context and classical histology of different types of allograft rejection and also the common entities that enter the differential diagnosis of allograft rejection, and provides practical approaches to liver allograft biopsy interpretation. In addition, some of the new developments in the field of liver transplant pathology are updated. The purpose of this review is to provide guidance for pathologists interpreting liver allograft biopsies, particularly those interested in developing expertise in the field of liver transplant pathology.

Complement membrane attack complex and protectin (CD59) in liver allografts during acute rejection

BACKGROUND/AIMS

The complement system is important in the rejection of xenografts, but very little is known about its activation in the rejection of allografts. Complement lysis is induced by the membrane attack complex (MAC), an aggregate of C5b, C6, C7, C8 and C9 molecules. The main defender against MAC is the CD59 molecule, also called protectin. In this study, the aim was to analyze the possible deposition of MAC and the fate of CD59 on distinct cell populations during liver allograft rejection.

METHODS

Liver allografts were monitored by frequent fine-needle aspiration biopsies (FNAB) to demonstrate the immunoactivation of rejection. To examine MAC and CD59 in the FNAB, in relation to the activation markers of rejection, IL2-receptor, MHC class II and ICAM-1 expression, specific monoclonal antibodies and immunoperoxidase staining were used.

RESULTS

Ten out of 21 consecutive liver transplants underwent a histologically confirmed episode of reversible acute rejection. In the FNAB, a significant increase of the activation markers IL2-receptor, class II and ICAM-1 correlated with the peak of inflammation during the episode. In association with inflammation, a significant deposition of MAC was recorded in neutrophils and lymphocytes infiltrating the graft and in the parenchymal cells. MAC deposition subsided together with the inflammation. A significant decrease in CD59 expression was seen in neutrophils during rejection, but CD59 expression on other inflammatory cells and hepatic tissue cells varied greatly.

CONCLUSIONS

Complement activation was seen in association with acute rejection of liver allografts and it led to MAC assembly on leukocytes and tissue cells. A decrease in CD59 expression was less clear-cut, but it may predispose the cells to complement-mediated elimination.

Role of nuclear medicine in liver transplantation

Orthotopic liver transplantation is now a very well-established technique for treating patients with end-stage liver disease. Since 1967, more than 26,000 liver transplants have been performed, including 15,000 in the United States. The overall 1-year survival rate is approximately 80% and 5-year survival is 70%. Nuclear imaging plays an important role in the management of liver transplant recipients before and after liver transplantation. The evaluation of candidates potentially includes liver-spleen scan for liver volume, multiple gated acquisition scan, adenosine or stress thallium study, bone scan, and quantitative ventilation perfusion scan for hepatopulmonary syndrome. In the post-transplant phase, the deconvolution analysis (which corrects for the problem of recirculation) is a promising tool for diagnosing rejection, although its role in the transplant population has to be established. A variety of nuclear medicine techniques are helpful in the postoperative diagnosis of biliary complications. By performing a semiquantitative analysis to discriminate hepatocyte dysfunction from biliary disease and measuring hepatocyte extraction fraction by deconvolution analysis and excretion, (T1/2 values measured by the nonlinear list squares technique) have been very promising.

Encephalopathy and neuropathy in end-stage liver disease before and after liver transplantation

The nervous system involvement of 8 patients with end-stage liver disease was evaluated by means of clinical neurological, neuropsychological, neurophysiological and neuroradiological investigation before and 6-12 months after a successful liver transplantation. Preoperatively, all subjects (7 women, 1 man; mean age 40 years, range 30-54 years) exhibited decreased muscle strength and 2 patients manifested clinical signs of polyneuropathy. In neuropsychological tests, slight visuoconstructive apraxia, and disturbances of verbal memory and cognitive function were observed. Magnetic resonance imaging (MRI) revealed cerebral lesions in two patients. After transplantation, muscle strength reverted to normal in all patients, polyneuropathy improved and in all but 2 patients recovery of neuropsychological functioning was observed. Clinical signs of encephalopathy had disappeared. All patients were emotionally better adjusted after transplantation. Four subjects showed new, albeit mild changes in neurophysiological and neuropsychological tests postoperatively. We conclude that the majority of neurological impairment disappeared after liver transplantation. We want to stress that evaluation of neurological sequelae of liver transplantation needs to be based on assessments both before and after liver transplantation.

Liver transplantation modifies serum cholestanol, cholesterol precursor and plant sterol levels

Proportions of cholesterol precursors (squalene, delta 8-cholestenol, desmosterol and lathosterol), plant sterols (campesterol and sitosterol) and cholestanol to cholesterol in serum were measured before and serially after liver transplantation in eight patients with primary biliary cirrhosis (PBC) and three with acute liver necrosis. The preoperative proportions of cholestanol were 12 and 3-times higher in the PBC and necrosis groups, respectively, than in a control group of 27 individuals, while those of lathosterol were low in both groups and the campesterol/sitosterol ratio in the PBC group. During the operation the proportions of cholestanol fell sharply and those of lathosterol rose especially in the PBC group. During the postoperative follow-up of 5 weeks the proportions of the non-cholesterol sterols were markedly improved especially in the necrosis group yet those of cholestanol remained high and the campesterol/sitosterol ratios low, particularly in the PBC group. The proportions of lathosterol increased gradually almost to the control limits within the postoperative 5-week period, whereas those of desmosterol decreased. The non-cholesterol sterol values were not related to acute rejections, while significant correlations of cholestanol to liver function tests was found especially at the end of the follow-up.

Liver transplantation restores low serum levels of very low density and high density lipoproteins in end-stage primary biliary cirrhosis

Amounts of serum lipids were determined in 10 women suffering from end-stage primary biliary cirrhosis (PBC) in order to evaluate the concentrations of and changes in very low density (VLDL), high density (HDL) lipoprotein cholesterol and apoprotein A-I before and after liver transplantation. The concentrations of some preoperative serum total lipids, especially HDL cholesterol and VLDL triglyceride, and apoprotein A-I, were significantly lower, but those of serum total triglycerides and cholestanol (a metabolite of cholesterol) were higher in the PBC patients than in 12 controls matched for age, sex, and body mass index. The relation between the serum concentrations of HDL cholesterol and cholestanol was markedly different before transplantation in the PBC group and in the control group. Liver transplantation was followed by a significant and rapid increase in serum apoprotein A-I and HDL cholesterol concentrations, which were affected by CMV and Klebsiella infections and acute rejections and immunosuppressive treatments. As a result the patients serum values did not quite return to normal during the three month follow up. The concentrations of serum VLDL cholesterol, triglycerides and cholestanol returned to normal during the follow up, and the changes in cholestanol were inversely related to the increases in amounts of HDL cholesterol. Thus, the restoration of low HDL concentrations after liver transplantation suggests that the liver plays a key role in HDL metabolism and indicates that concentrations of serum HDL cholesterol may be useful in monitoring the recovery of liver function.

Fine-needle aspiration biopsy in the monitoring of liver allografts

The diagnosis of acute liver allograft rejection is difficult, as clinical signs or liver function tests are too unspecific. The diagnosis is mainly based on biopsy histology. However, the liver core biopsy may be associated with complications. The fine-needle aspiration biopsy (FNAB) method, originally developed for the monitoring of renal transplants, is a reliable and atraumatic technique to diagnose acute cellular rejection of liver allografts. FNAB makes it possible to quantity the inflammation associated with rejection, and to monitor the response to anti-rejection therapy. Additional information is received from changes in liver parenchymal cells indicating tissue damage and/or possible hepatotoxic effects of the drugs used. In addition, FNAB may be helpful in differential diagnosis of infections, cholestasis or other complications. A good correlation between FNAB findings of acute liver rejection and histology has been reported. However, histological examination is needed to diagnose chronic rejection. Several liver transplant centres now use FNAB technology as a routine diagnostic tool.