Neutrophils are granule-containing, polymorphonuclear leukocytes that develop in the bone marrow from myeloid precursors. They play a central role in the innate immune response by destroying foreign particles either intracellularly in phagosomes or extracellularly by releasing neutrophil extracellular traps (NETs), and promoting acute inflammation. In humans, neutrophils are the most abundant circulating leukocyte, accounting for 50-70% of white blood cells, while 10-25% of circulating mouse leukocytes are neutrophils. Although neutrophils can be visually identified based on the shape of their nuclei and cytoplasmic granularity, they can also be identified by flow cytometry. Mouse neutrophils are commonly identified based on the cell surface expression of Ly-6G and CD11b/Integrin alpha M. Since mouse granulocytic myeloid-derived suppressor cells can also express these markers, neutrophils are frequently distinguished from these cells in mice based on their lack of expression of M-CSF R/CD115 and CD244/SLAMF4, along with an absence of immunosuppressive properties. In humans, neutrophils are distinguished from eosinophils and monocytes based on the expression of both CD15 and CD16/Fc gamma RIII on human neutrophils, along with the lack of expression of CD14. In addition, CD66b/CEACAM-8, CD11b/Integrin alpha M, CD33, and the cytoplasmic marker, myeloperoxidase, are other common markers that are used to identify human neutrophils.