Cytotoxicity assay by ⁵¹Cr release.

Peripheral blood NK cells were cocultured for 3 hours with K562 target cells. PIG-A mutant cells were less susceptible to NK cells than normal control cells. GPI⁺ (○), control cells (revertant) expressing GPI; and GPI⁻ (●),PIG-A mutant cells (mock transfectant) deficient in GPI. (A) Cytolysis by NK cells obtained from a representative healthy donor at various E/T ratios. (B) Relative decrease in the cytolysis of GPI⁻ cells in 13 separate experiments with NK cells of 13 healthy individuals. In each experiment, the cytolysis of GPI⁺ cells was set at 100% and the E/T ratio was 32:1. Each value represents the mean (± SD) of triplicate assays.