PDCD1 and viral infectious disease: The role of PD-1 polymorphisms on viral diseases is of an importance (Zheng et al., 2010[36]; Xiao et al., 2015[29]; Zhang et al., 2012[33]), but only few publications have investigated the role of PD-1 polymorphisms, especially in HCV infection outcomes (Xiao et al., 2015[29]).