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Isolation, Culture, and Identification of Natural Killer Cells

Several natural killer (NK) cell subsets have been described in humans and mice based on their phenotypic markers and functional capabilities. Human natural killer (NK) cells have been defined based on the level of cell surface expression of NCAM-1/CD56 and CD16 on CD3- lymphocytes. CD56dimCD16+ cells are found predominantly in the blood and spleen and are highly cytotoxic, while CD56brightCD16- NK cells are found in the lymph nodes and tonsils. CD56brightCD16- cells are potent cytokine producers, but have only weak cytotoxic potential prior to activation. In mouse, natural killer cells are defined based on the expression of CD161/NK1.1, Integrin alpha 2/CD49b, NKp46, Integrin alpha M/CD11b and CD27 on CD3- lymphocytes. Within this population of cells, three different subsets of mouse NK cells have been identified: CD11dimCD27bright, CD11bbrightCD27dim, and CD11bbrightCD27bright NK cells. These three subsets differ in their tissue distribution, cytokine production, and cytotoxicity. CD11bdimCD27bright cells are found primarily in the bone marrow and lymph nodes, CD11bbrightCD27dim cells are localized predominantly in the blood, spleen, lung, and liver, and CD11bbrightCD27bright cells are widely distributed. Upon stimulation, CD27bright NK cells produce higher levels of cytokines and are more cytotoxic than CD27dim cells.