CD81 and chronic hepatitis C virus infection: Aim of this study was to investigate whether soluble CD81 levels are increased in patients with chronic hepatitis C. Therefore, the concentration of soluble CD81 in the exosomal fraction p5 was compared between a cohort of 23 healthy controls and 37 patients with chronic hepatitis C. As shown in Figure 2, the serum CD81 concentration in fraction p5 was significantly higher in patients with chronic hepatitis C compared with healthy controls (Figure 2 A, B).