P4HB and type 2 diabetes mellitus: In addition, markers of UPR, such as BiP, PDI, and sXBP1, are increased in NK cells from T2D patients and ER stress is activated through PERK and IRE1 sensors, which are involved in UPR and that are causative of NKG2D down-modulation in NK cells from T2D patients (117) (Figure 2C).