XLP NK cell cytotoxicity against NK-sensitive target cell lines. The NK-sensitive cell lines K562 and Daudi or as a control an LCL were used as targets in chromium release cytotoxicity assays with: (A) NK clones derived from a healthy donor (top panel) or XLP1 (bottom panel) or (B) NK lines established from a healthy donor (top panel) or XLP8 (bottom panel). Results are expressed as the percentage of chromium release from the target cells at the different effector:target ratios.