CD38 and hepatitis C virus infection: Analysis of multiple surface markers associated with T cell or NK cell differentiation and activation (Figure 3, D and E) showed higher levels of CD38+ iNKT cells in peripheral blood samples of HCV RNA–positive PWID (mean 24.5%) compared with HCV RNA–negative PWID (mean 8.9%, P = 0.0008), which was consistent with the results from the late phase of acute hepatitis C. No apparent differences were observed regarding the other markers included in the analysis (Figure 3D).