CD274 and viral infectious disease: In HPV-HNSCCs, membranous expression of PD-L1 and significantly increased levels of mRNA of IFN-γ were found in the tonsillar crypts, As tonsillar crypts witnessed the initial HPV infection, and IFN-γ induces PD-L1 expression, this evidence might support the role of the PCD-1/PD-L1 interaction in creating an “immune-privileged” site for initial viral infection and subsequent adaptive immune resistance.31