MAPK3 and myocardial infarction: Immune cells, but not myofibroblasts, endothelial cells, or cardiomyocytes, were a prominent location for ERK1/2 activation throughout the course of acute MI in border and infarcted zones, but not remote and unaffected regions of the myocardium (Figure 3, A and B, and Supplemental Figures 7–9).