One study using flow cytometry found significantly increased CD4+CD73+CD39- and Treg populations in ME/CFS whole-blood samples, while a separate ME/CFS Treg study found a trend of higher CD39+CD73+ frequency in this illness, compared to healthy controls, further supporting the theory of anergic features in ME/CFS CD4+ T cells [94,159]. Here, CD4 is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.