Pro-inflammatory factors such as tumor necrosis factor-α (TNF-α), interleukin 6 (IL-6), interleukin 8 (IL-8), interleukin 18 (IL-18), interleukin 1β (IL-1β), or chemokine ligand 2 (CCL2) are also produced by WAT and are all increased in obesity [35]. Here, IL6 is linked to obesity due to melanocortin 4 receptor deficiency.