Hormones might be involved.
The immune system maintains an important balance between pro-inflammatory and anti-inflammatory cytokines. An excess of pro-inflammatory cytokines (e.g., interleukin [IL]-12) can lead to inflammation and tissue damage, whereas an increase in anti-inflammatory cytokines (e.g., IL-10) can lead to increased susceptibility to infections. In a crossover study of 11 healthy men, researchers evaluated the effect of sleeplessness on the balance of IL-12+ and IL-10+ monocytes.
Monocyte levels were measured at 1.5- to 3.0-hour intervals during a normal 24-hour sleep-wake cycle and during a 24-hour period without sleep. Levels of growth hormone, prolactin, cortisol, and norepinephrine were measured to assess their association with changes in IL-12+ and IL-10+ monocyte counts.
The ratio of pro-inflammatory to anti-inflammatory cytokine-producing monocytes during nighttime hours was four times higher when subjects were allowed to sleep than when they were kept awake; the daytime ratios for the two groups did not differ. Although the correlations were relatively weak, the percentage of IL-12+ monocytes was correlated positively with prolactin level and negatively with cortisol level, and the percentage of IL-10+ monocytes was correlated positively with norepinephrine level.
Comment: This small study supports the commonly held belief that sleeplessness affects immune function, although the clinical consequences of these changes in monocyte ratios are unclear. The findings also suggest that hormones play an intermediary role in this process.
— Jamaluddin Moloo, MD, MPH
Published in Journal Watch October 5, 2006
Citation(s):
Lange T et al. Shift of monocyte function toward cellular immunity during sleep. Arch Intern Med 2006 Sep 18; 166:1695-700.