Figure 1. Macrophage depletion prevents regeneration of the neonatal mouse heart.

(A) Neonatal mouse pups are intravenously injected with clodronate-loaded liposomes (yellow), which are phagocytosed by macrophages (red). Clodronate uptake results in macrophage apoptosis and subsequent depletion (blue). Loss of macrophages in neonatal mice results in scarring and fibrosis following MI. (B) In untreated pups, macrophages infiltrate the injured heart and are distributed uniformly throughout the heart (red) following MI. Macrophage infiltration into the heart is proposed to stimulate coronary neovascularization, via paracrine secretion of proangiogenic factors, to support myocardial regeneration. LAD, left anterior descending artery.