The potential of S100-A9 to cause endothelial dysfunction and damage, as well as its overexpression during inflammatory states and its proinflammatory nature, may be of relevance to ME/CFS, a disease which is characterized by endothelial dysfunction [11, 12, 14, 16, 17, 162] and (dysregulated) inflammation [26, 101, 104, 106]. Here, S100A9 is linked to endothelial dysfunction.