CCL2 and obesity due to melanocortin 4 receptor deficiency: From the in vivo models, it can be deduced that neutrophils, infiltrated into the hypertrophic adipose tissue in the early stage of obesity, mediate the recruitment and polarization of macrophages through the increased secretion of proinflammatory as well as macrophage recruiting chemotactic mediators (e.g., IL-6, tumor necrosis factor (TNF)-α, CCL2) [54,55].