Indeed, an in vitro study using sorted CD4+CXCR5+ blood Tfh cells from healthy controls (HCs) and chronic hepatitis C–infected patients (HCV) showed that Tfh cells from HCV patients produce less IL-21 but are equally capable of driving in vitro B-cell proliferation and differentiation into antibody-producing cells compared with healthy control cells [50]. Here, CD4 is linked to chronic hepatitis C virus infection.