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Natural killer cells are lymphocytes that identify and lyse tumor cells and cells infected with microbes. The ability of NK cells to recognize cells as foreign is dependent upon inhibitory and activating receptors on the target cells. The inhibitory receptors distinguish between normal and tumor or infected cells by the presence or absence of the major histocompatibility complex class I. The activating receptors are NKp46, NKp30, NKp44 and NKG2D. PMID: 14685277 In addition to their cytolytic function in the innate immune system, NK cells also function to regulate reciprocal interaction with dendritic cells, macrophages, T cells and endothelial cells and thereby affect immune response. PMID: 1842510 Patients that experience recurrent severe herpes infections, primary or secondary hemophagocytic lymphohistiocytosis, and suspected or known monogenic defects or patients who have received immune reconstitution post hematopoietic cell transplantation may lack the normal number or functionality of NK cells. The level of NK cell functionality is determined by various methods, including flow cytometry and chrominum-release assays. The chromium-release assay uses titrations of effector cells (that are assumed to be NK cells) that are incubated with the target cells. The level of chromium released by the target cells is then divided by the corrected level of chromium measured in the positive control to assess percent cytotoxicity. The flow cytometric methods measure cell-mediated immunity, particularly based on uptake of 7-amino-actinomycin D (7-AAD) or propidium iodide (PI) and Annexin V binding, to assess percent cytotoxicity of target cells by effector cells. PMID: 11470149 Interleukin-2 (IL-2) has been found to increase the reactivity of NK cells against target cells PMID: 23650441 and is used in some NK cell cytotoxicity assays. Source: Regenstrief LOINC

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Natural killer cell cytotoxicity
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