To confirm the causal role of the ATF4 branch of the ER stress pathway in impairing macrophage efferocytosis in vivo, we turned to the mouse model of obesity, which displays lipid accumulation, activation of ER stress, and defective efferocytosis in peritoneal macrophages as compared with lean mice. This evidence concerns the gene ATF4 and obesity due to melanocortin 4 receptor deficiency.