Despite these findings, studies of plasma cytokine levels have been inconclusive; findings include increased levels of interleukin (IL)-1 and tumor necrosis factor (TNF) [14], increased levels of IL-1α and IL-1β but normal levels of TNF [15], and no differences between CFS patients and healthy controls [16, 17]. This evidence concerns the gene IL1A and myalgic encephalomeyelitis/chronic fatigue syndrome.