Our body’s barrier tissues, which include the skin, eye surface, mouth, intestine lining, and urinary tract, are crucial for protection against external factors.
Innate lymphoid cells (ILCs) play a key role in defending these tissues by releasing cytokines that activate the immune system and regulate the gut microbiome in response to threats.
However, ILCs decrease naturally with age or due to certain health conditions.
These cells are produced in the bone marrow and travel in the bloodstream. But what triggers their movement to replenish depleted tissue ILCs?
A study by Michigan Medicine reveals that circadian rhythms govern this migration, aligning with Earth’s 24-hour day/night cycle.
Dr. Chang H. Kim’s team studied this process in mice, which are nocturnal creatures.
In both mice and humans, cortisol levels peak in the morning, inducing wakefulness, while a decline in cortisol and rise in melatonin and adenosine promote sleepiness.
Investigators found that progenitor cells (ILCPs) express clock genes, leading to time-specific activity patterns.
Specifically, cortisol boosts the activation of CXCR4 in ILCPs, keeping them in the bone marrow. Conversely, IL-18 and RORα stimulate S1PR1 in ILCPs, promoting their release from the bone marrow into the blood during rest.
Dr. Kim suggests that the body optimizes cell production by accumulating ILCPs during activity hours and releasing them during sleep.
This cycle is essential for maintaining sufficient levels of gut barrier tissue ILCs.
Disrupting circadian rhythm can lower tissue ILCs, increasing susceptibility to infection and microbiome imbalance.
Understanding the circadian mobilization of ILCs can have broad applications, potentially in stem cell research and therapies.
