The NKCCA was significantly increased after IL-2 (20 IU/mL) stimulation with the E:T of 25:1 for HCs being 49.67 ± 6.273 and 48.55 ± 5.129 for ME/CFS patients, respectively (p > 0.05); at 12.5:1 for HCs being 49.42 ± 7.256 and 52.68 ± 5.998 for ME/CFS patients, respectively (p > 0.05); and at 6.25:1 for HCs being 39.15 ± 6.347 and 39.08 ± 5.034 for ME/CFS patients, respectively (p > 0.05). Here, IL2 is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.