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Our immune system’s clocks and calendars could make us more vulnerable to infections and injuries at certain times of the day or in certain months of the year, suggests a new study. A better understanding of these rhythms could have implications for the prevention and treatment of diseases like Covid-19. It might also help explain why certain illnesses, like the flu, tend to strike in the winter, while the symptoms of other illnesses, like multiple sclerosis, often get worse in the summer.
Although recent studies have suggested that there may be seasonal or daily “circadian” rhythms in our immune function, this has not been confirmed in a large number of people until now.
“It has been clear for centuries that people are more susceptible to certain illnesses in the winter, but we still don’t really understand our body’s role in this,” said Dr Cathy Wyse, postdoctoral researcher at the Royal College of Surgeons. in Ireland, which led the new research.
To investigate, Wyse and his colleagues turned to blood drawn from some 329,261 participants in the British Biobank study – which followed the health of around half a million Britons for more than a decade – to see if the The time of day or season that these samples were collected had some effect on the immune cells they contained.
They found marked fluctuations in the number of white blood cells and markers of inflammation in the blood, suggesting that our immune function may be stronger or weaker, depending on the time of day or season. “This supports the idea that there could be endogenous clocks and calendars in the immune system,” said Wyse, whose research was published in preprint form and has yet to be reviewed by peers.
Importantly, these variations were not related to environmental or lifestyle factors, or vitamin D levels: “This suggests that such changes in our immune system are due to our body clocks – the innate mechanisms that allow us to follow time, ”said Dr Rachel Edgar of Imperial College London, who is studying how viruses can harness circadian rhythms to promote their spread.
This is because the daily fluctuations seen in this study mirror patterns Edgar previously documented in mice, with white blood cells collecting in lymph nodes early in the mouse’s active period and moving through the bloodstream as the mice progressed to their resting phase. What goes on in these lymph nodes is the key to our immune response to vaccines and viruses like Sars CoV-2: “In mice, the time of day they are faced with. [with a virus] has profound consequences on the immune response a few days later, ”said Edgar. “This, combined with evidence that the seasonal influenza vaccine appears to be more effective when given in the morning compared to the afternoon, strongly suggests that some Sars-CoV-2 vaccines may be more effective when administered. they are administered early in the day.
This theory has not been tested, and Wyse cautions against over-interpreting his results. However, from an evolutionary standpoint, it makes sense to coordinate the activities of your immune cells with when you are most likely to be active. “The simplest interpretation is that the immune system has evolved to better recognize and fight off potential pathogens during the day, because that’s when humans would be most likely to come into contact with it. pathogens, ”said Dr John O’Neill of the Medical Research Council’s Molecular Biology Laboratory in Cambridge, which previously showed that cells involved in repairing tissue damage migrate into wounds more quickly during the day.
“These results are an exciting confirmation of the fundamental importance of biological synchronization for human health,” said Professor Tami Martino, Distinguished Chair in Molecular Cardiovascular Research at the University of Guelph in Ontario, Canada. “From a lifestyle perspective, we can use this new understanding of the biological calendar to guide our behaviors, perhaps restricting our activity at night or in winter, to minimize our exposure to pathogens when we are. are the least resilient. ”
In separate research published last week, Martino found that the composition of the gut microbiome in mice also follows a day-night rhythm, and that feeding mice during their resting period – which disrupted those microbial rhythms – altered the ability of mice to heal the heart. pity.
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