This may be of pathophysiological relevance in the light of data demonstrating elevated IgA and IgM responses to lipopolysaccharide (LPS)/antigens of Gram-negative gut commensal bacteria and gut dysbiosis in patients afforded a diagnosis of CFS via the Fukuda criteria (Maes et al. 2006; Morris et al. 2016b; Morris and Maes 2013b). Here, CD40LG is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.