P4HB and viral infectious disease: However, data indicate that PDI is directly involved in the regulation of endoplasmic reticulum stress15, 19 and oxidative stress,20 resulting in the development of cancer, neurological degenerative changes, immune and viral infections, and infertility.14, 19, 21, 22, 23 In this study, we for the first time connected PDI with the simultaneous increases in VSMC proliferation and apoptosis in vitro and in vivo and confirmed different PDI expression across individual VSMCs (Figure 8).