Immunogenetics of hepatitis B virus infection (2002)

Infection is defended by the host's innate and acquired protective mechanisms. The acquired immune system is represented by humoral and cell-mediated immune (CMI) response. Hepatitis B virus (HBV) infection can persist by avoiding the host's immune clearance. Hepatitis B virus infection has diverse clinical outcomes ranging from spontaneous recovery from infection to chronic hepatitis, liver cirrhosis and hepatocellular carcinoma (HCC). Although the key factors affecting the outcome of HBV infection are unclear, these various clinical outcomes may rely on interactions between viral, host and environmental factors. Viral factors such as virulence, viral amount, mode of viral infection, infection period and duration and genomic variability of the virus are some of the most important factors determining clinical outcome. However, viruses with identical genomic structure may be associated with diverse disease outcomes in different hosts.1 The family study of monozygotic and dizygotic twins indicated that host genetic factors are major determinants of susceptibility to infection.2 In infectious diseases, candidate gene studies have implicated several immunogenetic polymorphisms. The definition of such a candidate gene is that it encodes for products that influence the susceptibility or resistance to a specific disease. To determine if these genes contribute to the disease phenotype, its polymorphisms should be examined in disease association or family studies. Human leukocyte antigen (HLA) variation has been associated with susceptibility or resistance to malaria, tuberculosis, leprosy, AIDS, and hepatitis virus persistence. Variations in the tumor necrosis factor (TNF) gene promoter have also been associated with several infectious diseases. Chemokine receptor polymorphism affects both the susceptibility to HIV-1 infection and the progression to AIDS. Whole genome linkage analysis of multicase families is now being used to map and identify new loci affecting susceptibility to infectious diseases.3 The recent wide use of the molecular biological technique has led to the development of our ability to identify genetic polymorphisms, and may present us with a means of elucidating the pathogenesis of chronic B viral liver disease. Initial genetic study of HBV focused on HLA associations. Currently, recent advances in molecular biology technique, such as the genome-wide scan or large-scale polymorphism screening, allows investigators to screen large numbers of subjects and identify new genes found to be resistant or susceptible to infection. In the near future, immunogenetic studies may play an important role in our understanding of diverse clinical outcomes or of therapeutic response.4 Hepatitis B virus is a DNA virus, and its clinical course following initial infection is diverse. It varies from spontaneous recovery to chronic persistent infection that might progress to chronic hepatitis, cirrhosis, or result in the development of HCC. Various disease courses after HBV infection appear to be related to hepatocyte damage, caused not only by the HBV itself but also by the host's immune response. Because strong virus-specific T lymphocyte response to HBV has been associated with viral clearance, an inappropriate viral antigen presentation to T lymphocytes, controlled by the major histocompatibility complex (MHC) gene, may induce persistent HBV infection. Therefore, immunogenetic factors may have a role in determining the susceptibility of an individual to chronic HBV infection.3-7 In humans this is known as the HLA system and is located on the short arm of chromosome 6, with genes arranged in three clusters, which consist of class I, class II, and class III molecules (Fig. 1). Variations in HLA class I and II molecules control viral antigen recognition by T lymphocytes and may thus affect either the nature and/or the magnitude of immune response. The genetic map of the human major histocompatibility complex (MHC). The MHC is located on the short arm of chromosome 6. Differences in the MHC class II allele sequence decide whether antigenic peptides are bound and presented by the MHC class II molecule to the CD4+ T-helper (Th) cells. Therefore, such differences prove the statement that persistent infection may be associated with specific MHC class II alleles. Thursz et al. found a negative association between HLA-DRB1*1302 and viral persistence.8 This association has recently been found to be independent of racial differences in a European study by Hohler et al. and in a Korean study by Ahn et al.6, 9 In the present study we investigated the HBV markers and HLA-DR phenotypes of 1272 Koreans. Subjects were categorized into three different groups: the unexposed group (UE; n = 946) with negative HBV markers; the chronic carrier group (CC; n = 83), who were hepatitis B surface antigen (HBsAg)-positive; and the spontaneously cleared group (SC; n = 243), who were HBsAg-negative with antibodies to HBsAg (anti-HBs) and hepatitis B core antigen (anti-HBc). Human leukocyte antigen-DR6 was significantly more frequent in 69 of 243 subjects in the SC group (28.4%) than in eight of 83 subjects in the CC group (9.6%; P < 0.001; relative risk (RR) = 3.72). Human leukocyte antigen-DR9 was significantly more frequent in the CC than in the SC groups (P < 0.001; RR = 0.33). Human leukocyte antigen-DR13 had a stronger association with the clearance of HBV than the other HLA-DR6 subgroup. Our data indicate that HLA-DR6, especially HLA-DR13, is one of the host factors that influence immune response to HBV, and may be associated with the self-elimination of HBV in Koreans. The relationship between various clinical manifestations and HLA type has been the subject of several studies, but no definitive relationship has as yet been found, primarily because of inconsistent results. Tumor necrosis factor-α promoter polymorphism, mannose binding protein, and vitamin D receptor have been investigated as potential candidate genes.3, 4, 10-15 Mannose-binding lectin (MBL), known as mannose binding protein, is a serum lectin that plays a role in innate immunity. Mutations are found at codon 52, 54 and 57 and those mutations lead to low and near absent serum MBL levels in heterozygotes and homozygotes. Yuen et al. reported that codon 54 mutation of MBL was associated with progression of disease in chronic hepatitis B infection.15 However, data from other studies did not support that association. The active form of vitamin D is an immunomodulatory hormone and the vitamin D receptor gene has polymorphism. Bellamy et al. suggested that these polymorphisms were found to be associated with persistent HBV infection.16 Numerous cytokines are involved in cell-mediated immune response. The importance of the cytokines TNF-α and interferon (IFN)-γ for the clearance of HBV was only recently emphasized by a number of findings. Tumor necrosis factor-α is a lymphokine produced by activated macrophages and monocytes that is a potent immunomodulator and proinflammatory cytokine involved in infectious and immuno-inflammatory diseases.17 The gene encoding TNF-α is located within the class III region of MHC between HLA-B and HLA-DR. The G to A transitions in the promoter region at positions −163, −238, −308 and −376 are well-known polymorphisms. Among them, two polymorphisms of the TNF-α promoter in region −308 and −238 may influence HBV persistence by altering TNF-α expression. The promoter polymorphism at −308 has higher transcriptional activity than that in the absence of the polymorphism, but there is some debate about the positive correlation between the promoter polymorphism of TNF-α and TNF overexpression/overproduction.10-13 Hohler et al. investigated the TNF-α promoter polymorphism in 71 patients with chronic HBV infection; in 32 subjects who had spontaneously recovered from acute HBV infection; and in 99 healthy controls. They assumed the existence of an association between the TNF-α promoter polymorphism at position −238 and the development of chronic HBV infection. They also suggested that this promoter variant appears to be linked to defective viral clearance and may be a host factor that contributes to the development of chronic hepatitis B.13 We investigated the relationship between TNF-α promoter polymorphism, and the clearance or persistence of HBV. We studied a total of 212 patients who were classified into four groups according to the status of their HBV infection: (i) UE group (n = 55) with negative HBV markers; (ii) SC group (n = 54), who were HBsAg-negative with antibodies to HBsAg (anti-HBs) and hepatitis B core antigen (anti-HBc); (iii) hepatitis B non-progression group (NP; n = 31) who were HBsAg-positive, HBeAg-negative, and with normal transaminase; and (iv) the hepatitis B progression group (PG; n = 72) who were HBsAg-positive with chronic hepatitis, cirrhosis or HCC. The HLA-DR genotyping was performed using the ELPHA DRB high resolution technique, and the TNF-α promoter polymorphism was tested by using ABI Prism® SNaPshot™ ddNTP Primer Extension Kit (Biotest Diagnostics, NJ, USA). (Primers: −308 sense: 5′-AATAG GTTTT GAGGG GCATG-3′; −308 antisense: 5′-TTTTT TCTGG AGGCT GAACC CCGTC C-3′; −238 sense: 5′-TTTTT TTTTT TTTTT TAGAA GACCC CCCTC GGAAT C-3′; −238 antisense: 5′-TTT TTTTT TTTTT TTTTT TTTTT ACTCC CCATC CTCCC TGCTC-3′). In the present study the TNF-α promoter polymorphism at position −308 and HLA-DRB1*13 were strongly associated with the clearance of HBV infection (Table 1). However, a substantial genetic association was also suspected between TNF 308 and HLA-DRB1*13 (Table 2). Hepatitis B immunogenetics is an immature field. Although inconsistent data discourage efforts to identify the key genes that affect HBV infection, large-scale studies using the new molecular technologies may well overcome this problem in the near future. Recent immunogenetic studies have documented reproducible associations between HLA class II alleles and susceptibility to persistent HBV infection. In addition, TNF promoter associations have encouraged ongoing infectious disease studies of other cytokine genes with known polymorphisms, including, interleukin (IL)-4, IL-10, and IL-1. However, other host genetic factors influencing the outcomes of HBV infection such as severity of liver disease, response to antiviral therapy or progression of HCC need to be documented. Further multicohort studies may clarify preliminary association and help to identify other potential candidate genes.