CCL2 and metabolic syndrome: Furthermore, the widespread presence of M1 macrophages and leptin polymorphisms due to excess fat tissue during childhood may impede lung growth and development by stimulating proinflammatory cytokines such as IL-6, IL-12, tumor necrosis factor-alpha (TNF-α), and monocyte chemoattractant protein 1 (MCP-1), which are associated with chronic inflammation and other comorbidities such as insulin resistance or metabolic syndrome, as mentioned later in this review [61,62,63].