C5AR1 and obesity due to melanocortin 4 receptor deficiency: In an animal model of diet-induced obesity, however, no difference in pancreatic islet morphology and beta cell mass was observed between wild-type and C5aR1-knockout animals, although C5aR1-deficient mice exhibited improved insulin sensitivity and fewer macrophages, particularly pro-inflammatory M1 macrophages, in the adipose tissue [35].