Natural killer (NK) cells, also known as large granular lymphocytes, are mononuclear cells that mediate cytolysis against target cells lacking MHC Class I or Class II molecules. They also regulate the immune response, contribute to natural resistance against tumor cells, and produce cytokines.
Mononuclear cells (containing lymphocytes with natural killer activity) are incubated for 2 hours with K562 target cells that have been prestained with PKH-2, a lipophilic dye that binds to the cell membrane and fluoresces green. When NK cells kill K562 cells, the target cells become permeabilized and take up propidium iodide, fluorescing bright red/orange. The percentage of killed target cells containing propidium iodide is then measured by flow cytometry. When lymphocytes are incubated with target cells in the presence of IVIg or Intralipid, inhibition of cytotoxicity may be observed.
Send at room temperature. Do not refrigerate. Deliver to the laboratory within 24 hours.
If a specimen is older than 48 hours, lymphocytes will be isolated and viability assessed. If viability is >80%, the assay will be performed. If viability is <80%, the specimen will be rejected.
Flow Cytometry
| NK Assay Full Panel % Killed at: | NK Cell Inhibition Panel % Killed at: | NK Assay Follow-up % Killed at: | NK basic panel % Killed at: | Normal Range |
| 50:1 | 50:1 | 50:1 | 50:1 | 10 - 40% |
| 25:1 | 25:1 | 25:1 | 25:1 | 5 - 30% |
| 12.5:1 | 12.5:1 | 12.5:1 | 3 - 20% | |
| IgG 12.5 mg/ml, 50:1 | IgG 12.5 mg/ml, 50:1 | |||
| IgG 12.5 mg/ml, 25:1 | IgG 12.5 mg/ml, 25:1 | |||
| IgG 6.25 mg/ml, 50:1 | Intralipid 1.5mg/ml, 50:1 | |||
| IgG 6.25mg/ml, 25:1 | Intralipid 1.5mg/ml, 25:1 |
(Note: NK Assay Follow-up does not include IVIg or Intralipid)