CD56brightCD16-NK Subset was decreased in the CFS/ME group. Percentage of NK cells stained positive for CD56brightCD16- was significantly low in the CFS/ME group at the T1 and at T2. The white bars represent control data while the black bars represent CFS/ME data. (B) Cluster analysis showing the overall cytotoxic activity in the whole participant group. Data are presented in the form of log of the total events collected via flow cytometery ± SEM. *Signifies statistical significant results relative to controls.