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 of Sciences.

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 diseases.