TNF and obstructive sleep apnea syndrome: OSA has been associated with systemic inflammation with increased circulating levels of pro-inflammatory cytokines, including TNF-α, IL-6 and IL-8, independent of obesity.[5–7,31] Our data showing decreases in IL-8 and its receptor gene expression during control exposure (Table 2) are consistent with circadian variations of IL-8 levels peaking in the early morning hours.[32] This circadian decline was no longer present during intermittent hypoxia suggesting that IL-8 may have been up-regulated.