Altered NK cell subset homeostasis in PNH. (A) Cell surface expression of the GPI-linked proteins CD48, CD59, and CD160 on the NK cells (gated on CD56+CD3^neg cells) of a healthy control (HC) and a PNH patient. Staining with fluorescent aerolysin (FLAER) demarcates GPI+ from GPI^neg cells. (B) CD56^bright and CD56^dim NK cell subsets present in the peripheral blood of PNH patients (plots gated on CD56+CD3^neg cells). The top 2 rows show 3 patients with all 4 subsets of NK cells (denoted p1.number), and the bottom 2 rows show 3 patients in which the GPI+CD56^bright NK cells made up less than 0.02% of the total GPI+ NK cells (denoted p2.number). The 4 subsets of NK cells are indicated in different colors, according to the key. NK cells from p2.10 were analyzed on 3 occasions; the first 2 visits are shown here, and the third visit, together with sequential analysis of 3 other patients, is shown in supplemental Figure 2. Across the cohort of 47 patients, the size of the GPI^neg NK cell population varied from ∼1% to ∼99% of the total NK cells (supplemental Figure 1), in agreement with previous findings.⁸  An “E” after the patient number indicates the patient was receiving eculizumab at the time of analysis. (C) Frequency of CD56^bright NK cells as a percentage of total GPI^neg or total GPI+ NK cells compared with healthy controls. P values (calculated using the Mann-Whitney nonparametric test) are shown for statistically different data.