Many activities of the immune system follow rhythmic daily cycles. Now researchers have found that some immune cells have their own circadian clocks.
Achim Kramer of the Charité Medical University in Berlin and his colleagues took immune cells and tissues from mice at regular intervals throughout the day. They found that macrophages — cells that form part of the immune system's first line of defence against bacterial infections — from the spleen, lymph nodes and abdominal area express circadian clock genes. In addition, they showed that about 8% of macrophage genes are expressed rhythmically.
The authors also report that the secretion of immune modulators by spleen macrophages in response to bacterial toxins follows circadian rhythms.