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.

The team focused on the most abundant immune cells in our bodies, called 'neutrophils', which are a type of white blood cell. These cells move quickly to the site of an infection and kill invading bacteria.

The researchers 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.

"In earlier studies, we had observed that immune responses peaked in the morning, during the fish's 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.

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.

Most of our cells have circadian clocks to tell them what time of day it is in the outside world, in order to regulate the body's activities. 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.

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