GIPR and obesity due to melanocortin 4 receptor deficiency: Hence, the increased expression of pEIF2α may explain the increase in Xbp1s. Altogether, these results reveal that absence of the GIPR signaling in immune cells alters the expression of type 2 immune mediators in adipocytes, associated with the induction of the PERK-EIF2a ER stress pathway during the development of obesity.