Immunological aspects of clinical liver transplantation

Relevance of HLA compatibility in living donor liver transplantation: the double-edged sword associated with the patient outcome

HLA compatibility in living donor liver transplantation (LDLT) seems relevant to the acceptability of graft livers because LDLT recipients often share most or some part of HLAs with the respective donors. This study retrospectively investigated whether HLA compatibility affected the outcome of LDLT. Three hundred ninety LDLTs were performed in this hospital, and 346 pairs of HLAs (HLA-A, B, DR) were retrieved from the medical record between October 1996 and March 2011. The dates of the deaths were censored when a recipient apparently died of or was retransplanted by other causes than graft failure because of host-versus-graft (HVG) response to purely analyze the outcomes of LDLT in view of HVG response. The relationship between HLA compatibility and graft-versus-host disease (GVHD) was also analyzed. No recipients with recipient-against-donor HLA mismatch (R→D MM) 0 experienced graft failure by HVG response. On the other hand, three of five recipients with "R→D MM 0" together with "donor-against-recipient MM 3" died of fatal GVHD. HLA compatibility in LDLT not only affected the long-term acceptance of graft livers but also the risk of fatal GVHD.

Immune cholangitis: liver allograft rejection and graft-versus-host disease

A pronounced similarity exists between liver allograft rejection and graft-versus-host disease (GVHD) in the damage and eventual destruction of small intrahepatic bile ducts. Although an immunologic reaction has an important role, precisely identifying the target antigens or reason for persistence of the immune response has been difficult. An important difference between GVHD and liver rejection is the development of obliterative arteriopathy only in rejection. The three main histopathologic features of acute rejection are a predominantly mononuclear but mixed portal inflammation, subendothelial inflammation of portal or terminal hepatic veins (or both), and bile duct inflammation and damage. In acute rejection, a controversial issue is determining when therapeutic intervention is needed. The recommended approach is to base treatment on a combination of histopathologic changes and liver injury or dysfunction. Chronic rejection, which usually does not occur before 2 months after transplantation, is characterized by two main histopathologic features: (1) damage and loss of small bile ducts and (2) obliterative arteriopathy. Acute GVHD begins within the first month after transplantation and most commonly involves the skin, gastrointestinal tract, and liver, whereas chronic GVHD usually develops more than 80 to 100 days after liver transplantation and affects 30 to 50% of long-term survivors. Recognition of the early, cellular stages of chronic GVHD is important in preventing irreversible damage.

Comparison of intrahepatic lymphocytes from normal and growth hormone transgenic mice with chronic hepatitis and liver cancer

Mice expressing an ovine growth hormone-mouse metallothionein promoter fusion gene (METoGH mice) develop chronic hepatitis which becomes progressively more severe over time, hepatocellular adenomas, and eventually carcinoma in the oldest animals. T-lymphocyte expression of activation/memory-associated markers was compared between liver and blood lymphocytes isolated from METoGH and non-transgenic mice at 7, 10 and 12 months of age. The percentage of intrahepatic lymphocytes (IHL) which were CD4+ was markedly diminished in METoGH mice at all times. CD4+ and CD8+ IHL in METoGH mice expressed Ly-6A/6D at increased density, and were CD45RBlo at later time-points. Ly-6C+ and NK1.1+ CD4+ cells, which are common in normal mouse liver, were found at decreased frequency in METoGH livers. Further analysis demonstrated that, as a proportion of total T-cell receptor (TCR) alpha beta cells, NK1.1+ TCR alpha beta int CD4+ cell numbers (NKT cells) were diminished in the livers of METoGH mice. Observations made in METoGH mice support the hypothesis that sustained liver inflammation and hepatocellular injury may be linked to liver cancer. Additionally, it is possible that the relative lack of NKT cells may create an environment permissive for the growth of liver tumours.

Chronic rejection of liver transplants revisited

We examined 27 hepatectomy specimens to assess the frequency of foam cell endovasculitis and bile duct loss in chronic rejection. Arterial lesions, defined as total occlusion by subintimal foam cells and/or fibromuscular proliferation, were found mainly in hilar and septal arteries, whereas bile duct loss, defined as the absence of bile ducts in more than 50% of portal tracts, affected mainly small tracts. Both were found in 20 livers (74%). In two livers (7%) there was significant bile duct loss but no arterial lesions, whilst in five cases (19%) there were occlusive arterial lesions but no bile duct loss. Small arteries were involved in only 10% of the cases. These results indicate that in one-third of the cases arterial and bile duct lesions develop independently of each other, suggesting different pathogenetic pathways. In addition, liver biopsy may not be pathognomonic since small arteries are involved in only 10% of cases and bile duct loss may not be extensive. In such cases the diagnosis of chronic rejection should only be made in the presence of progressive clinical deterioration.

Immunogenetics of chronic liver diseases

The genetic background of autoimmune diseases becomes more and more evident. Immunogenetics comprises the analysis of genes and their products located at the region 6p21 on the short arm of chromosome 6, which is also known as the major histocompatibility complex (MHC). MHC class I and II genes are highly polymorphic. The complement genes C2, C4A, C4B, and BF, which are also polymorphic, became known as MHC class III genes. In autoimmune hepatitis type 1, there is a dual association for white persons with either HLA-A1-B8-DR3 or HLA-DR4. In patients from Japan, autoimmune hepatitis type 1 is predominantly associated with HLA-DR4. This dual association is confirmed at the DNA level. Whereas only limited data are available for autoimmune hepatitis type 2, the association of primary biliary cirrhosis with HLA-DR8 is based on several studies. Primary sclerosing cholangitis is associated with HLA-B8-DR3 and -DR52a. This association was confirmed at the DNA level because of a significant increase of the DRB3*0101 allele. For DRB3*0101-negative individuals, a second association with DRB5*0101 (= DR2) was described. Further analysis of the hypervariable region of the HLA class II molecule indicates that lysine at position 71 is crucial for autoimmune hepatitis type 1 in white persons, whereas position 13 is important for people from Japan. In contrast, leucine at position 35 is important for patients with primary biliary cirrhosis, whereas leucine at position 38 is an important risk factor for primary sclerosing cholangitis. The MHC class III allele C4A-QO is significantly increased in autoimmune hepatitis type 1 and 2 and in primary biliary cirrhosis. Advances in immunogenetics will certainly increase our knowledge of the etiology and pathogenesis of immune-mediated liver diseases, which hopefully will lead to more specific therapeutic interventions.