CCL2 and obesity due to melanocortin 4 receptor deficiency: Obesity triggers adipocyte hypertrophy and hyperplasia, reduces the anti-inflammatory factor APN, and increases pro-inflammatory cytokines such as IL-6, IL-1β, TNF-α, and chemokines (CCL2, CCL3, and CXCL8), leading to the infiltration of immune cells (M1-type macrophages, CD8+ and CD4+ T lymphocytes, and B lymphocytes) and consequently promoting adipose inflammation (42).