“My biological clock is ticking.”
We’ve heard people say this phrase - maybe even said it ourselves - but what do we mean exactly? Often this is a reference to a female of reproductive age. For example, you might hear a woman say her “biological clock” is “ticking” when referencing the limited amount of healthy years for a female to become pregnant and give birth. However, the biological clock can also be a reference to circadian rhythm.
The circadian rhythm is the body’s internal clock that influences activities like waking and sleeping in response to environmental cues like light in the morning and darkness in the evening. The circadian rhythm is both natural and subject to change by a person’s environment, like a paramedic who adapts to work at night and sleep during the day. This internal clock also affects more than just sleeping and waking; eating, body temperature, and hormone product is also under the influence of circadian rhythm, thus linking it to metabolic and hormonal health conditions.
Twenty thousand neurons of the “suprachiasmatic nucleus” (SCN) in the hypothalamus of the brain make up this internal clock. A new study from scientists at the Douglas Research Centre, the Maisonneuve-Rosemont Hospital Research Centre, and McGill University found that the same clock plays a role in how well the immune system responds to external foes.
More specifically, they observed that CD8 T cells function differently at different times during the day, something that makes a significant difference in the context of sensitive clinical administrations, like vaccines.
CD8 T cells are immune cells produced in the thymus that express a CD8 receptor (like CD4 T cells express CD4 receptors). CD8 T cells are often called cytotoxic T cells for their ability to target and destroy infected and cancerous cells.
The study included a post-vaccination mouse model to observe how the immune response changed with and without a functional circadian rhythm. Scientists found that the strength of CD8 T cell response varied during different time points throughout the day, excluding experimental mice who were missing certain genes linked to the circadian rhythm. For example, the response to the vaccine was not as strong during the day as it was at night
“Identifying the mechanisms through which the biological clock modulates the T cell response will help us better understand the processes that regulate optimal T cell responses,” explained one of the study’s scientists, Nathalie Labrecque, Ph.D. “This knowledge will contribute to improving vaccination strategies and cancer immune therapies.”
Sources: McGill University, Proceedings of the National Academy of Sciences, National Institute of General Medical Sciences, British Society for Immunology