The body’s internal clock affects the immune system the way scientists in the burgeoning field of circadian immunology are beginning to unwind.
Why is this important: Harnessing the effects of the circadian clock on the immune system could help improve the effectiveness of certain treatments for a range of diseases and conditions, a new book and scientific journal suggests.
How it works: The central body clock, or suprachiasmatic nucleus (SCN), is a collection of about 20,000 neurons in the brain that receives signals from the eye when it detects light or other environmental cues from the body.
- The signals trigger the components of the clock – a network of genes that regulate the production of different proteins in neurons. (Other cells in the SCN also slow down the activity of neurons). The quantities of these proteins in the cell oscillate over 24 hours, defining the rhythm of the clock.
- The central timekeeper then coordinates the body’s other clocks and sets the pace for regulating body temperature, sleep schedule, hormone release, and a host of other biological processes.
- “Without this precise regulation by an internal clock, our whole biology would be in chaos,” writes Russell Foster, professor of circadian neuroscience at the University of Oxford, in his new book, “Life Time” about the science of biological clock. and its relationship to health.
The immune system is also under the control of the clock: the functions of different immune cells have been shown to oscillate over the course of a day.
- The circadian clock “synchronizes the whole body with the outside world but we don’t know exactly how an immune cell sees it”, explains Christoph Scheiermann, an immunologist at the University of Geneva and co-author of a recent review on the circadian clock. immune system.
What’s new: Studies suggest that the time a vaccine is given can alter the immune system’s response to it.
- The immune response to vaccination against influenza or tuberculosis in two different studies tended to be greater in people vaccinated in the morning compared to those who received injections later in the day.
- Two other small studies found that the immune response to COVID-19 vaccination depended on the time of day – but the optimal time depended on the vaccine given.
- Previous work has found that when drugs or treatments for certain cancers, asthma, heartburn and other conditions are given can influence their effectiveness.
But, but, but … Variations between a person’s immune system and their body’s rhythms mean that the best time for treatment can vary from person to person.
- The rhythms are generally the same for most individuals and his likely recommendations can be made for most of the population most of the time, says Jacqueline Kimmey, professor of microbiology at UC Santa Cruz.
- But making recommendations for individuals isn’t possible “until we have better ways to measure the ‘time’ that someone’s body says it is, and more specific knowledge about the” time “we should do something,” she said.
- There may be differences due to genetics, behavior and environment. The “morning” in a night shift worker’s body can be 3 p.m., so if he goes for a shot at 8 a.m. he may not benefit from the effects of time, says John Hogenesch, professor of human genetics and director of the Center for Circadian Medicine at Cincinnati Children’s Hospital Medical Center.
- Changing the time may also not be practical for certain therapies like cancer treatments that hospitals have limited capacity to administer at particular times.
The big picture: Scientists have known about immune rhythms for decades, but new tools allow them to better understand the signals and components of body clocks.
- Immune rhythms coordinate and balance the different responses of the immune system throughout the day.
- Parts of the adaptive immune system – which learns to target pathogens through vaccination or infection – are throttled against new invaders during the day.
- At other times, the responses are rejected so that the immune system does not turn on itself and trigger an autoimmune disease.
The innate immune system, a more immediate and global response to pathogens is also controlled by the clock.
- In a study published last week, researchers found that when mice and marmosets rested, skin cells produced proteins that protected the animals against staph infections and boosted the innate immune response.
The impact: Sleep disturbances can alter the biological clock and weaken the immune defense system, making it more vulnerable to disease.
- It can also cause the body to produce stress hormones, which suppress the immune system.
- Some viruses, such as influenza, also disrupt the circadian rhythm of the immune system, dampening the immune response and enhancing the virus’s own replication.
- The malaria parasite reproduces in sync with the circadian clock and releases a flood of parasites that overwhelms the immune system at night when its guard isn’t as high, writes Foster.
When people are infected or treated is “a huge variable that we don’t pay attention to,” Kimmey says.
- Knowing that the adaptive immune system is not as activated at night as it is during the day, employers can take steps to better protect shift workers, such as providing protective equipment to frontline medical workers caring for those with the disease. of a virus, says Foster.
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