The adult murine heart has a sparse, phagocytically active macrophage population that expands through monocyte recruitment and adopts an 'M2' phenotype in response to Th2 immunologic challenge

In conclusion, in the healthy heart resident macrophages are relatively sparse and have a phagocytic role. Following Th2 challenge this population expands due to monocyte recruitment and adopts an 'M2' phenotype associated with increased tissue fibrosis.