AT macrophages (ATM), which can account for up to 50% of the cellular content in the obese AT, are the primary source of pro-inflammatory cytokines (e.g., IL-6, TNF-α, IL1-β), and have been shown to be centrally important in obesity-related metabolic dysfunction [38,39,40,41]. Here, IL1B is linked to obesity due to melanocortin 4 receptor deficiency.