Soluble TNF alpha receptor 1 and IL-6 plasma levels in humans subjected tothe sleep deprivation model of spaceflight

Background: The extent to which sleep loss may predispose astronauts to a s tate of altered immunity during extended space travel prompts evaluation wi th ground-based models. Objective: we sought to measure plasma levels of selected cytokines and the ir receptors, including the putative sleep-regulation proteins soluble TNF- alpha receptor (sTNF-alphaR) I and IL-6, in human subjects undergoing 2 typ es of sleep deprivation during environmental confinement with performance d emands, Methods: Healthy adult men (n = 42) were randomized to schedules that varie d 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 deprivati on (TSD). Plasma samples were obtained every 6 hours across 5 days and anal yzed by using enzyme-linked immunoassays for sTNF-alpha RI, sTNF-alpha RII, IL-6, soluble IL-2 receptor, IL-10, and TNF-alpha. Results: Interactions between the effects of time and sleep deprivation lev el were detected for sTNF-alpha RI and IL-6 but not for sTNF-alpha RII, sol uble IL-2 receptor, IL-10, and TNF-alpha. Relative to the PSD condition, su bjects in the TSD condition had elevated plasma levels of sTNF-alpha RI on day 2 (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 leve ls of sTNF-alpha RI and IL-6, messengers that connect the nervous, endocrin e, and immune systems. These changes appeared to reflect elevations of the homeostatic drive for sleep because they occurred in TSD but not PSD, sugge sting that naps may serve as the basis for a countermeasures approach to pr olonged spaceflight.