In the present report, we established a K562 cell line useful for an enzyme release assay of human natural killer (NK) activity. Human myelogenous leukemia cell line, K562, was transfected with a plasmid carrying Escherichia coli β-galactosidase (β-gal) gene. A colony that permanently expresses the enzyme activity was isolated, and designated K562/Zneo. Incubation of K562/Zneo cells (1 X 104) with nonadherent human peripheral blood lymphocytes (PBL) resulted in the release of β-gal activity depending on the incubation time and the number of effector cells. Released β-gal activity was assayed sensitively by using 4-methylumbelliferyl-β-D-galactoside, a fluorescent substrate. The cytolytic activity of PBL was augmented significantly when the cells were preincubated with interleukin-2 for 20 h. This enzyme release assay showed a comparable sensitivity to that of 51Cr release assay. Thus, K562/Zneo cell line is thought to be useful for the nonradioactive assay of human NK and lymphokine-activated killer activities.
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