CXCR3 and viral infectious disease: Human Tfh cells that express the surface receptors CXCR5 and PD-1 but lack the expression of CXCR3 are known as circulating counterparts of germinal center Tfh cells (cTfh), are able to provide help to memory B cells in vitro and are associated with neutralizing HIV antibody responses (12), whereas CXCR3+ Th1-biased cTfh (cTfh1) cells may either fail to support memory B cells in vitro (12, 13) but have also shown to correlate with antibody responses to HIV (14, 15), HCV (16–18), other viral infections (19) and after vaccination (20–23) in humans and animal models.