Cytotoxic activity in patients with FHL. Using the standard ⁵¹Cr-release assay, polyclonal-activated NK cells derived from patients with FHL3 and FHL2 were compared with those from age-matched healthy individuals for cytolytic activity against various target cells. (A) NK cells from a large group of healthy donors (mean of values, ▪, error bars showing ± SD), from 5 different patients with FHL3 (open symbols and crosses) and 2 different patients with FHL2 (• and ▾) were tested against the melanoma FO-1 and the B-EBV cell line 221 at different E/T ratios, as indicated. (B) NK cells from 2 representative healthy individuals and patients with FHL3 and FHL2 were tested against iDCs derived from a single allogeneic healthy individual either in the absence (□) or in the presence (▪) of anti–HLA class I mAb. The E/T ratio used was 10:1. (C) NK cells from 1 representative healthy individual and 1 patient with FHL3 (UPN 293), and 1 patient with FHL2 (UPN 314) were tested against the Fcγ-Rc⁺ P815 in the absence or in the presence of mAb to different triggering receptors, as indicated. The E/T ratio used was 4:1. Error bars indicate standard error of the mean.