Soluble TNF-α receptor 1 and IL-6 plasma levels in humans subjected to the sleep deprivation model of spaceflight

Background: The extent to which sleep loss may predispose astronauts to a state of altered immunity during extended space travel prompts evaluation with ground-based models. Objective: We sought to measure plasma levels of selected cytokines and their receptors including the putative sleep-regulation proteins soluble TNF-α receptor (sTNF-αR) I and IL-6 in human subjects undergoing 2 types of sleep deprivation during environmental confinement with performance demands. Methods: Healthy adult men (n = 42) were randomized to schedules that varied in severity of sleep loss: 4 days (88 hours) of partial sleep deprivation (PSD) involving two 2-hour naps per day or 4 days of total sleep deprivation (TSD). Plasma samples were obtained every 6 hours across 5 days and analyzed by using enzyme-linked immunoassays for sTNF-αRI sTNF-αRII IL-6 soluble IL-2 receptor IL-10 and TNF-α. Results: Interactions between the effects of time and sleep deprivation level were detected for sTNF-αRI and IL-6 but not for sTNF-αRII soluble IL-2 receptor IL-10 and TNF-α. Relative to the PSD condition subjects in the TSD condition had elevated plasma levels of sTNF-αRI on day (P =.04) day 3 (P =.01) and across days 2 to 4 of sleep loss (P =.01) and elevated levels of IL-6 on day 4 (P =.04). Conclusions: Total sleep loss produced significant increases in plasma levels of sTNF-αRI and IL-6 messengers that connect the nervous endocrine and immune systems. These changes appeared to reflect elevations of the homeostatic drive for sleep because they occurred in TSD but not PSD suggesting that naps may serve as the basis for a countermeasures approach to prolonged spaceflight.