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Keywords:

  • sleep;
  • circadian rhythm;
  • immune system;
  • human;
  • cytokines;
  • leukocytes;
  • prolactin;
  • growth hormone;
  • cortisol;
  • hormones;
  • vaccination;
  • immune response

Many immune parameters show systematic fluctuations over the 24-h day in human blood. Circulating naive T-cells and production of proinflammatory cytokines, like interleukin-12 (IL-12), peak during nighttime, whereas cytotoxic effector leukocytes and production of the anti-inflammatory cytokine IL-10 peak during daytime. These temporal changes originate from a combined influence of the circadian system and sleep. Both brain functions act synergistically and share neuroendocrine effector mechanisms to convey control over immune functions. Sympathetic tone and cortisol levels show a circadian nadir during nighttime and are further suppressed by sleep, whereas growth hormone and prolactin show a circadian peak during nighttime and are further enhanced by sleep. Thus, the circadian system and sleep jointly evoke a unique endocrine constellation that is extremely effective in inducing changes in leukocyte traffic and a shift toward proinflammatory type 1-cytokines during the nocturnal period of sleep, that is, an action with strong clinical implications.