Cytolytic deficiency types in HLH tested against K562.

Distinct cytotoxic deficiency types 1, 2, 3, and 4 were identified by testing NAL and LAK from patients against K562 targets, with and without agglutinating mitogen (PHA) and at different target incubation times (4 hours, 16 hours). Killer function was calculated as lytic units (LU) from the regression analysis of 3-4 titrations of the initial effector/target cell ratio ranging between 100:1 and 30:1. Mean values of the results are shown as a horizontal bar in the scatter plots of 4-hour (filled circles) and 16-hour (open circles) incubation time in the assay. The cutoff level of 10 LU for the minimum cytolytic function by NK cells (4-hour incubation time, K562 targets) is given as a horizontal dashed line.