The immune system is known to have a circadian rhythm; however, how circadian rhythms might affect immune homeostasis and physiology more broadly is unclear. A new paper now provides evidence that γδ T cells (a type of innate T cell) produce IL-17 in a rhythmic fashion, which is essential for de novo lipogenesis in adipose tissue and influences whole-body homeostasis.

To confirm that IL-17A and IL-17F are expressed in a circadian rhythm, the researchers used flow cytometry to analyse γδ T cells from the adipose tissue of mice, which showed that the expression of the cytokines was regulated by the molecular clock. In mice under homeostatic conditions, IL-17A levels peaked during the night (the active phase). “Using a small molecule enhancer (SR9009) of the molecular clock and genetic models (ArntlΔVav1 (also known as Bma1) and ArntlΔIl7r) to suppress the molecular clock, in collaboration with Henrique Veiga Fernandez’s laboratory in Lisbon, we found that clock genes control IL-17 production by γδ T cells in adipose tissue,” add Lynch and Douglas.