Fig. 4

Fig. 4

Comparative analyses in neonatal and adult mice after cardiac injury. In neonatal mice, embryonic macrophages with M2-like properties expand and dominate the injured area, leading to minimal inflammation, angiogenesis, and vigorous CM proliferation. T cells are also prone to differentiate into Tregs at this stage, resolving inflammation and stimulating CM proliferation by secreting mitogens [138]. The high reparative capacity leads to functional recovery in neonatal mice. However, in adult mice, this M2-like resident macrophage population is replaced, or out-numbered, by monocyte-derived macrophages which are prominently pro-inflammatory [59]. This functional difference leads to an unresolved scar and contractile dysfunction