The sudden sleepiness that
accompanies the onset of many illnesses occurs when the immune system interferes
with the body's circadian clocks, Swiss researchers report on Monday.
The immune system cytokine, TNF-alpha, induces the fatigue associated with
some infections and autoimmune diseases, according to their papers published in
the online early edition of the U.S. journal Proceedings of the National Academy
Like other body rhythms, sleep cycles are controlled by a circadian clock.
Previous research implicated the cytokine TNF- alpha in causing sleepiness, so
Gionata Cavadini and colleagues from University Hospital Zurich investigated the
effects of TNF- alpha on the genes involved regulating circadian rhythms.
In cells, the cytokine suppressed the expression of several clock genes, an
effect that was duplicated in mice treated with TNF-alpha. In addition, mice
treated with TNF-alpha showed increased rest periods during their activities.
Further investigation revealed that TNF-alpha only suppresses those clock
genes that have a specific element known as the E-box. While it is still unclear
whether increased rest is a boon to host defense mechanisms, the researchers
note that increased fatigue decreases quality of life in many autoimmune