Because of the resemblance of CFS symptoms with so called “sickness behavior” including the symptoms fatigue, post-exertional malaise and reduced activity levels, CFS has often been suggested to involve increased activity of pro-inflammatory cytokines, such as IL-1β and TNF-α which are considered to play a key role in inducing sickness behavior during acute illness ([55]; Kelley et al., [56]). Here, TNF is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.