TNF and obesity due to melanocortin 4 receptor deficiency: Consistently in this study, HFD feeding was observed to induce obesity and increased serum TNFα levels, and apparent infiltration of ATMs were observed in WT HFD mice, which also showed obvious characteristics of insulin resistance, i.e., increased fasting insulin levels, postprandial hyperglycemia, impaired glucose tolerance, and insulin tolerance (Figs. 4 and 6).