IL21 and myalgic encephalomeyelitis/chronic fatigue syndrome: Within the ME/CFS cohort, 67 individuals expressed IL-21 concentrations within normal levels (0–115 pg/mL), and 302 exhibited significantly heightened IL-21 levels, ranging from 125.52 to 130,000 pg/mL (86%, P < 0.0001), while in the control cohort, only 9 individuals (11.68%) had IL-21 levels above the normal range.