Chapter 34 : Measurement of NK-Cell Activity in Humans

Abstract:

In most cases, natural killer (NK) cells activity is determined in the peripheral blood and only rarely in the target tissue, largely because it is difficult to isolate NK cells from diseased tissues in humans. Many of the newer cytotoxicity assays are based on flow cytometry and are nonradioactive. In combination with flow cytometry for the enumeration of cells expressing the NK-cell phenotype, the assay can provide a quantitative estimate of NK-cell function during human health and disease. The NK activities of fresh and cryopreserved peripheral blood mononuclear cells (PBMC) from the same individuals have been compared and have encountered differences as large as 100%, although PBMC from certain individuals can be cryopreserved without such losses in cytolytic function. NK cells can be subdivided into two functionally distinct populations on the basis of CD56 and CD16 expression on the cell surface. Biologic variability controls: fresh PBMC from the same healthy donors are obtained repeatedly at various time intervals and used to chart the biologic variability in NK-cell activity over time. Measurements of NK activity are difficult to perform in a clinical laboratory setting. They require considerable expertise, constant vigilance, and extensive quality control and quality assurance.