Daytime boosts immunity, scientists find

A breakthrough study, led by scientists at Waipapa Taumata Rau, University of Auckland, has uncovered how daylight can boost the immune system’s ability to fight infections.

Evidence has shown that disruption of our internal body clock through the likes of shift work or jet lag makes people more susceptible to infections, so the researchers wanted to find out what in the body contributed to that susceptibility.

“In earlier studies, we had observed that immune responses to infection peaked in the morning, during the animals’ early active phase,” says lead researcher Associate Professor Christopher Hall, from the Department of Molecular Medicine and Pathology.

“We think this represents an evolutionary response such that during daylight hours the host is more active so more likely to encounter bacterial infections,” says Hall.

However, the scientists wanted to find out how the immune response was being synchronised with daylight.

They focused on the most abundant immune cells in our bodies, called ‘neutrophils’, a type of white blood cell. These cells move quickly to the site of an infection and kill invading bacteria.

The scientists used zebrafish, a small freshwater fish, as a model organism, because its genetic make-up is similar to ours and they can be bred to have transparent bodies, making it easy to observe biological processes in real time.

With this new study, published in Science Immunology, and led by two doctoral researchers, neutrophils were found to possess a circadian clock that alerted them to daytime, and boosted their ability to kill bacteria. [Link to come]

The circadian clock is a 2.5 billion-year-old cellular timekeeper that allows organisms to adapt to the rhythms of day and night.

These molecular clocks are present in almost every cell and tissue in the body, telling them what is going on in the outside world and coordinating physiological processes like metabolism, hormone release, and sleep-wake cycles.

Light has the biggest influence on resetting these circadian clocks.

“Given that neutrophils are the first immune cells to be recruited to sites of inflammation, our discovery has very broad implications for therapeutic benefit in many inflammatory diseases,” Hall says.

“This finding paves the way for development of drugs that target the circadian clock in neutrophils to boost their ability to fight infections.”

The research was funded through the Royal Society of NZ’s Marsden Fund.

This work was a collaboration between the Hall laboratory and the Chronobiology Research Group, led by Guy Warman and James Cheeseman, at the Faculty of Medical and Health Sciences.

Current research is now focussed on understanding the specific mechanisms by which light influences the neutrophil circadian clock.