PPIA and viral infectious disease: In particular, CyPA (i) acts as an intracellular chaperone during viral replication for different viruses (33, 34); (ii) behaves as an intracellular sensor that favors viral infection (hampering the innate immune response [35], and regulating the sensitivity to host restriction factors [36]); and (iii) partakes in target cells invasion by HIV-1 and SARS-CoV (51, –, 53), but not by SARS-CoV-2 (54), mediating virus binding to the CD147 receptor.