Furthermore, patients with acute or chronic infection with HCV genotype Akt inhibitor 3a did not mount T-cell responses to this epitope region, and their autologous viral sequences showed no evidence

of T-cell pressure. Finally, we found a significantly higher frequency of HLA-B27 positivity in patients with chronic HCV genotype 3a infection compared to genotype 1 infection, indicating that there is no protection by HLA-B27 in HCV genotype 3 infection. Conclusion: Our data indicate that the protective effect of HLA-B27 is limited to HCV genotype 1 infection and does not expand to other genotypes such as genotype 3a. This can most likely be explained by intergenotype sequence diversity leading to the loss of the immunodominant HLA-B27 epitope in viral strains other than genotype 1. Our results underline the central role of a single HLA-B27-restricted epitope-specific CD8+ T-cell response in mediating buy I-BET-762 protection in HCV genotype 1 infection. (HEPATOLOGY 2010;51:54–62.) Human leukocyte antigen B27 (HLA-B27) is a prominent major histocompatability complex (MHC) class I-allele in human immune biology. It is associated with autoimmune diseases such as ankylosing spondylitis and related spondyloarthritis, but also confers protection in viral

infections. Indeed, it is associated with slow disease progression in human immunodeficiency virus (HIV) infection1, 2 and a high rate of spontaneous viral clearance in hepatitis C virus (HCV) infection.3 The mechanisms by which HLA-B27 mediates susceptibility to rheumatic disease and at the same time protection in infectious diseases are thought to be related, with several theories being currently discussed. This includes theories suggesting that the role of HLA-B27 is independent from epitope presentation MCE or that HLA-B27 might even be in gene linkage with another, decisive factor. It has also been suggested that the strong immunogenicity of HLA-B27 is linked to its unusual cell biology, including its tendency to misfold or to build noncanonical forms such as heavy chain homodimers, or the failure of B27 ligands to engage KIR3DL1, leading to an increased

natural killer cell activation.4, 5 A putative arthritogenic peptide has not been identified so far, further complicating the analysis of mechanisms contributing to the association between HLA-B27 and spondyloarthritis. In contrast, the protective role of HLA-B27 in HIV and HCV infection has been linked to single, immunodominant CD8+ T-cell epitopes.1, 6 In both infections, escape from the CD8+ T-cell response targeting this epitope is difficult to achieve. In HIV, one mutation is typically selected during the early phase of infection. However, this single mutation is not sufficient for immune escape, as the variant is still targeted. Full immune escape is only achieved when a second mutation develops at the main HLA-B27 binding anchor, arginine at position 2 of the epitope.