How is the immune system linked to the circadian clock?

Dr. Lora Hooper, a professor at the University of Texas Southwestern Medical Center and an investigator at the Howard Hughes Medical Institute, is investigating the relationship between the immune system and the circadian system in the gut.

The microbiome researcher was recently elected to the National Academy of Sciences in the US. GMFH editors interviewed her about one of her ongoing topics of study.

Dr. Lora Hooper, UT Southwestern Medical Center, Dallas

Dr. Lora Hooper, UT Southwestern Medical Center, Dallas

“The question is, why would the adaptive immune system be regulated by the circadian system?” says Hooper.

“The reason that’s a paradox is [that] circadian biology, by definition, is biology that fluctuates over a 24-hour period. It’s a short time scale, whereas the development of adaptive immune cells such as we have been studying in the gut requires up to two weeks. That’s a long-term proposition.”

Hooper reports her lab did not observe differences in the number of T cells in the gut on a circadian time scale. But that doesn’t mean the immune system and the circadian clock are unrelated.

“[One] way in which the circadian clock is used by animals is to synchronize processes,” she says. “You can synchronize a complicated process, so that in T cell development you have cells [that] get exposed to antigen and then they go through a series of developmental steps. This will happen over a whole population of cells. It’s much more efficient to make sure that all the cells that have sensed antigen at the same time go through these developmental steps at the same time.” In this situation, the developmental ‘status’ of the body’s T cells, rather than their absolute numbers, would change with the clock.

She proposes a further idea: “Maybe it’s a way of segregating in time two incompatible processes. With T cell development you have commitment to develop into a specific kind of T cell — that’s one part of the developmental pathway. The other can be something like proliferation. They can’t happen at the same time. In fact, they probably require two very different tissue microenvironments… You don’t want to shuttle those cells to a different place, but separating those processes in time by synchronizing them to different phases of the circadian clock, you can do it.” She adds, “We know that the commitment pathway and the proliferation pathway happen on opposite phases of the circadian clock.”

Further study of the relationship between the immune system and the circadian clock may eventually lend insights into human lifestyle factors that potentially disrupt immune system processes.

See here for more about the research in Dr. Lora Hooper’s lab.

Kristina Campbell
Kristina Campbell
Science writer Kristina Campbell (M.Sc.), from British Columbia (Canada), specializes in communicating about the gut microbiota, digestive health, and nutrition. Author of the best selling Well-Fed Microbiome Cookbook, her freelance work has appeared in publications around the world. Kristina joined the Gut Microbiota for Health publishing team in 2014.  Find her on: GoogleTwitter