TAC1 and myalgic encephalomeyelitis/chronic fatigue syndrome: Theoharides et al. [54] suggested that the role of mast cells as an “immune gate to the brain”, which can be stimulated by neuropeptides such as substance P, known to be increased in the cerebrospinal fluid (CSF) of FM patients [55], or sex hormones such as estrogens, possibly accounts for women’s overrepresentation in FM and CFS/ME [56,57,58].