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C.locks and calendars within our immune systems could make us more susceptible to infection and injury at certain times of the day or months of the year, a new study suggests. A better understanding of these rhythms could have implications for the prevention and treatment of diseases such as Covid-19. It could also help explain why some diseases, such as the flu, tend to strike in the winter, while the symptoms of other diseases, such as multiple sclerosis, often worsen in the summer.
Although recent studies have suggested that there may be seasonal or daily “circadian” rhythms in our immune function, this had not been confirmed in large numbers of people until now.
“It has been clear for centuries that people are more susceptible to certain diseases in the winter, but we still don’t really understand the role our bodies play in this,” said Dr Cathy Wyse, postdoctoral researcher at the Royal College. of Surgeons of Ireland, who led the new research.
To investigate, Wyse and colleagues turned to blood collected from some 329,261 participants in the UK Biobank study – which tracked the health of around half a million Britons for more than a decade – to see if the time of day or season in which these samples were collected had no bearing on the immune cells they contained.
They found clear fluctuations in white blood cell counts and markers of inflammation in the blood, suggesting our immune function may be stronger or weaker, depending on the time of day or season. “It supports the idea that there may be endogenous clocks and calendars in the immune system,” said Wyse, whose research has been published as a preprint and has not yet been peer-reviewed.
Importantly, these changes were not related to environmental or lifestyle factors, or to 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 keep track of time, ”said Dr Rachel Edgar of Imperial College London, who studies how viruses can exploit circadian rhythms to help spread them.
bod In fact, the daily fluctuations observed in this study mirror the patterns Edgar previously documented in mice, with white blood cells gathering in lymph nodes at the beginning of the mice’s active period and moving through the blood as the mice progress to their resting phase. What happens in those lymph nodes is key to our immune response to vaccines and viruses like SARS CoV-2: “In mice, the time of day they are challenged. [with a virus] has profound consequences for the immune response days later, “Edgar said.” This, coupled with evidence that the seasonal flu vaccine appears to be more effective when given in the morning than in the afternoon, strongly suggests that some Sars-CoV vaccines -2 can work best if given early in the day. “
This theory has not been tested and Wyse cautions against over-interpretation of its results. However, from an evolutionary perspective, 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 be better at recognizing and fighting potential pathogens during day, because this is the time humans are most likely to come into contact with pathogens, “said Dr John O’Neill of the Cambridge Medical Research Council’s Molecular Biology Laboratory, who had previously shown that cells involved in tissue damage repair migrate to wounds more quickly throughout the day.
“These findings are an exciting confirmation of how critically important biological time is to human health,” said Prof Tami Martino, distinguished president of cardiovascular molecular research at the University of Guelph in Ontario, Canada. “From a lifestyle perspective, we can use this new understanding of biological time to guide our behaviors, perhaps limiting our activity during the night or in the winter seasons, so as to minimize our exposure to pathogens in the moments when we are less resistant “.
In a 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 the mice during their rest period – which disrupted these microbial rhythms – compromised the ability of mice to heal from heart damage.
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