For example, HIV and hepatitis C virus infection are associated with an increase in CD10−CD19+CD20+CD21−CD27− B cells that express the inhibitory molecule Fc receptor-like-4 (FcRL4) (Charles et al., 2008; Moir et al., 2008), cells that are largely absent in the blood of healthy individuals. Here, FCRL4 is linked to hepatitis C virus infection.