Carnegie Mellon University

Natural Killer (NK) Cell Cytotoxicity (PCS1)

Sample Collection

Blood samples for assessment of natural killer cell cytotoxicity were collected on two occasions, 1 and 2 weeks prior to Quarantine.  Samples were drawn using standard venipuncture into heparinized vacuum tubes and stored at room temperature until assay.


Natural killer (NK) cell cytotoxicity was measured using a flow cytometry-based, whole blood assay at effector to target cell ratios of 100:1, 50:1, 25:1, and 12.5:1 1. To assess the reliability of the NK cell cytotoxicity assay, duplicate blood samples were collected from 60 subjects and submitted to the laboratory for analysis. Laboratory technicians were blind to this procedure. Values derived from the duplicate samples were highly correlated, r = .92, P <  .001. In order to obtain a maximally reliable assessment of basal natural killer cell cytotoxicity, values obtained from the two blood draws were averaged. The association between cytotoxicity measures at the two blood draws was r = .50, P < .001. Values are expressed in lytic units, derived using the method described by Bryan et al., (1992)2.

NK cell cytotoxicity assays were performed at the Immunologic Monitoring and Diagnostic Laboratory of the University of Pittsburgh School of Medicine.


1 Fletcher, M.A., Baron. G.C., Ashman, M.R., Fisehl, M.A., & Klimas, N.G. (1987). Use of whole blood methods in assessment of immune parameters in immunodeficiency states. Diagnostic Clinical Immunology, 5, 69-81.

2 Bryan, B., Day, R., Whiteside, T. L., Herberman, R. B. (1992).  Calculation of lytic units for the expression of cell-mediated cytotoxicity. Journal of Immunological Methods, 146, 91-103.