New problem linked to ‘jet lag’

Disrupting the internal clock of mice can confuse the animals’ immune systems

These gray, fingerlike shapes are the lining of a mouse’s intestine. The glowing green spots show pockets of immune cells called TH17. Extra cells of this type showed up after scientists disrupted the body clocks of mice. The finding suggests that resetting the body’s internal clock may impair immunity. 

Xiaofei Yu, Shipra Vaishnava and Yuhao Wang

Many processes in the body naturally turn on or off with a near-clocklike precision. Sleeping and changes in body temperature, mood and metabolism — the process of turning food into energy — all follow a cycle. This cycle repeats on a near-daily, or circadian, schedule. It’s driven by a master internal “clock,” a clump of brain cells that serve as a timekeeper. Now scientists have found that a confused clock may impair a person’s immune system, a collection of cells that fight infection and disease.

The body clock can get out of whack when a person travels to a distant place in a different time zone or works the night shift. Such disruptions may cause extreme tiredness, called jet lag in travelers. The new finding may help explain why people whose clocks are off may be more likely to suffer from some immune disorders.

The new study was conducted with mice. Still, its results may help scientists better understand how confused clocks affect people, Lora Hooper told Science News. And it’s not just night-shift workers or world travelers who might be affected. “None of us go to sleep when the sun sets or get up when the sun rises,” Hooper observes. She’s an immunologist, or a scientist who studies the immune system. She works at the University of Texas Southwestern Medical Center in Dallas, where she directed the new study.

Cells of the immune system usually help fight off infections and toxic invaders. But when the cells pile up, they can cause problems. And that’s the case with TH17 cells. These immune soldiers normally fight harmful germs and fungi. Usually they are good guys, Hooper says. But get too many together at one time and they could get rowdy.

“It’s like if you get too many football fans together at the same time,” she says. “They can riot.”

These cells normally kill germs by causing inflammation. It’s a common body response to injuries. But too much inflammation can backfire, she notes. It could even underlie a variety of diseases, including asthma, allergies, arthritis and heart disease.

Hooper and her team reset the body clocks of mice by six hours. They did this by changing when the animals woke up and were exposed to light. The experiment mimicked the jet lag travelers experience when they journey far enough that their waking and sleeping times no longer match what their body clock was used to.

Changes occurred in the gut of mice experiencing Hooper’s lab version of jet lag. Lots of TH17 cells accumulated. Hooper and her coworkers didn’t find a similar hoard of immune cells in the guts of mice whose body clocks continued to keep normal time.

The scientists also exposed mice to chemicals that can trigger immune problems. These chemicals were more likely to trigger inflammation in jet-lagged mice than in mice whose body clocks were operating normally. That suggests that resetting the internal clock may make an animal more likely to develop immune disorders.

Hooper’s group published its new study November 8 in the journal Science.

Dan Littman is an immunologist at New York University’s Langone Medical Center and did not work on the new study. He says the findings offer researchers who study inflammation new issues to probe. Resetting the body’s internal clock may even disturb other roles of the immune system.

“This is a new area of exploration,” he told Science News. “The big picture is not quite there yet, but it’s certainly something important to follow up on.”

Power Words

circadian  Recurring naturally on a 24-hour cycle.

circadian rhythm  Biological functions such as body temperature and sleeping/waking times that operate on a roughly 24-hour cycle.

gut  Colloquial term for an organism’s stomach and/or intestines. It is where food is broken down and absorbed for use by the rest of the body.

immune system  The collection of cells and their responses that help the body fight off infection.

immunity  The ability of an organism to resist a particular infection or poison by producing and releasing special protective cells.

inflammation  The body’s response to cellular injury; often involves swelling, redness, heat and pain.

metabolism  The set of life-sustaining chemical reactions that take place inside cells. These reactions enable organisms to grow, reproduce, move and otherwise respond to their environments.

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