To further explore the potential mechanism of action of the Lr-CFS, we examined the role of the ecto-5′-nucleotidase CD73 and the adenosine A2A receptor in mediating the effects on TNF-α-induced IL-8 production, as ATP was found in both Lr-CFS and Lh-CFS (41.7 vs. 9.2 nM, respectively). Here, CXCL8 is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.