ERAP1 and viral infectious disease: For example, CALR suppresses IFN-α production and antiviral activity in the context of hepatitis B virus infection [67], ERAP1 induces cleavage of cytokine receptors [65,66], and syndecan-4 (SDC4) negatively regulates retinoic acid-inducible gene I (RIG-I)-mediated signalling during virus infection [75].