CCR6 and viral infectious disease: Previous studies showed that Tfh (CXCR5+CD4+CD3+) cell subsets played a critical role in viral infections, including chronic HBV infection, which included Tfh type-1 (Tfh1) (CXCR3+CCR6-), Tfh2 (CXCR3-CCR6-), Tfh17 (CXCR3-CCR6+) and Tfh1/17 (CXCR3+CCR6+) cells based on the expression of CXCR3 and CCR6 (Schmitt et al., 2014; Tuzlak et al., 2021; Yoshitomi and Ueno, 2021; Chen et al., 2022).