CD81 and Insulin resistance: This result is in agreement with previous studies in which beige fat loss leads to glucose intolerance and insulin resistance.19–21 We are aware of the possibility, however, that metabolic organs other than beige fat may contribute to impaired glucose homeostasis in PpargCD81 KO mice, given the recent report that CD81 is expressed in immature pancreatic β cells,22 although fasting insulin levels were not different between the genotypes (Figure S2J).