TNF and fibromyalgia: Heightened levels of circulating inflammatory cytokines have been observed in both ME/CFS (CRP, TNF-α, interleukin-2, interleukin-4, and transforming growth factor-β; Groven et al., 2019; Strawbridge et al., 2019) and fibromyalgia (IL-6 and Interleukin-8; Yepez et al., 2022).