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. CD56^dimCD16+ cells are found predominantly in the blood and spleen and are highly cytotoxic, while CD56^brightCD16- NK cells are found in the lymph nodes and tonsils. CD56^brightCD16- 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: CD11^dimCD27^bright, CD11b^brightCD27^dim, and CD11b^brightCD27^bright NK cells. These three subsets differ in their tissue distribution, cytokine production, and cytotoxicity. CD11b^dimCD27^bright cells are found primarily in the bone marrow and lymph nodes, CD11b^brightCD27^dim cells are localized predominantly in the blood, spleen, lung, and liver, and CD11b^brightCD27^bright cells are widely distributed. Upon stimulation, CD27^bright NK cells produce higher levels of cytokines and are more cytotoxic than CD27^dim cells.