The Maxpar Human Monocyte/Macrophage Phenotyping Panel Kit identifies and phenotypes monocytes and macrophages. Monocytes circulate in the blood, bone marrow, and spleen and constitute approximately 2–12% of total human leukocytes. Monocytes have been considered the systemic reservoir of myeloid precursors for renewal of tissue macrophages and dendritic cells, although there are DC and macrophage subpopulations that originate independently of monocytes. Recruited monocytes are innate effectors of the immune response to microbes, and they kill pathogens via phagocytosis, production of reactive oxygen species (ROS), nitric oxide (NO), myeloperoxidases, and inflammatory cytokines. Monocytes can be categorized based on the expression of CD14 and CD16 as classical (CD14+CD16−), intermediate (CD14+CD16+), and nonclassical (CD14loCD16+).