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Figure 1. Plasma concentrations of sIL-6R, sgp130, DS-sIL-6R, and the percentage of IL-6-producing monocytes. Parameters were measured in 15 men during a regular sleep-wake cycle (filled circles) and during 24 h of continuous wakefulness (open circles). A) sIL-6R concentrations distinctly increased during late sleep (after 2:00 h) when REM sleep is predominant. Analysis of data during 24 h of wakefulness did not reveal any circadian rhythm. B) Concentrations of sgp130 were not influenced by sleep or circadian rhythm. C) Concentrations of DS–sIL-6R, like total sIL-6R concentrations, were increased by sleep but this rise was delayed by 
6 h, peaking at 14:00 h. D) Percentage of the total number of monocytes producing IL-6 (determined after LPS stimulation by flow cytometry) was not changed by sleep but showed a pronounced circadian rhythm. Mean (±SE) are shown. Shaded area indicates bedtime. **P < 0.01; *P < 0.05 for pairwise comparison at single time points between conditions.
