Case–control studies assessing the cerebrospinal fluid collected from ME/CFS patients compared to MS comparator samples indicate a markedly disturbed pattern of CNS immune activation in ME/CFS patients with noted elevations of CCL1 (eotaxin) and an inverse relationship between interleukin 1 receptor antagonist and colony-stimulating factor 1, colony-stimulating factor 2 and interleukin 17F, without effects on interleukin 1α or interleukin 1β. The gene discussed is IL17F; the disease is myalgic encephalomeyelitis/chronic fatigue syndrome.