Studies on molecular mechanisms regulating HBV replication showed that CyPA interacts with the small surface proteins (SHBs) of the HBV surface antigen (HBsAg).56 It was hypothesized that CyPA binds to SHBs and is secreted along with HBsAg particles.53 Thus, CyPA may function as a cell-intrinsic sensor able to recognize HCV and HBV proteins in order to promote viral infection and replication. Here, PPIA is linked to viral infectious disease.