S100A9 and myocardial infarction: In MI, neutrophils are recruited to the infarcted myocardium, where they undergo NETosis and release S100 Calcium Binding Protein A8 (S100A8) and S100 Calcium Binding Protein A9 (S100A9), upregulating C-X-C motif chemokine receptor 4 (CXCR4) expression in other neutrophils.