CD81 sequence and susceptibility to HCV infection

Background: Several cell surface molecules have been shown to have hepatitis C virus (HCV) binding properties and may serve as receptors to facilitate viral entry into cells. The large extracellular loop (LEL) of CD81 has been shown to bind the HCV envelope protein E2. Previous studies have demonstrated several critical residues for the CD81-HCV E2 interaction. We hypothesised that sequence variation in the CD81 LEL may result in altered susceptibility to HCV infection.

Methods: Three groups of cases were studied: HCV antibody positive but HCV RNA negative cases with spontaneous viral clearance, HCV antibody and HCV RNA positive chronically infected cases, and also cases with a long history of intravenous drug usage at high risk of HCV infection who were termed HCV exposed but uninfected cases. CD81 sequencing was performed in two ways. Firstly, genomic DNA was extracted from whole blood samples and the exonic sections of the gene encoding the CD81 LEL were amplified in four sections by PCR and subsequently sequenced. Secondly, the whole LEL (≈700 bp) was sequenced from cDNA made following RNA extraction from peripheral blood mononuclear cells.

Results: In total, 61 cases had their genomic DNA sequenced; 21 cases of spontaneous clearance, 15 chronic HCV, and 25 HCV exposed but uninfected cases. Of these 61, 23 also had the whole length LEL sequenced from cDNA—11 spontaneous clearers, five chronically infected, and seven exposed but uninfected. No sequence variation was found in any of the cases studied by either method, including the section of the gene coding the residues most important for CD81-HCV E2 binding.

Conclusions: The large extracellular loop of CD81 is a highly conserved molecule. There are no common differences in genomic sequence that influence susceptibility to, or outcome of, HCV infection.