In a new study, University of Auckland scientist Christopher Hall and his colleagues focused on neutrophils, a type of white blood cell that play a key role in antibacterial immunity.
Yi Du et al. identified a light-responsive cell-intrinsic timer that controls time-of-day variations in antibacterial activity. Image credit: Summerstock.
The study authors used zebrafish 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,” Dr. Hall said.
“We think this represents an evolutionary response such that during daylight hours the host is more active so more likely to encounter bacterial infections.”
However, the researchers wanted to find out how the immune response was being synchronized with daylight.
With this study, 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,” Dr. Hall said.
“This finding paves the way for development of drugs that target the circadian clock in neutrophils to boost their ability to fight infections.”
The study appears in the journal Science Immunology.
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Lucia Yi Du et al. 2025. A light-regulated circadian timer optimizes neutrophil bactericidal activity to boost daytime immunity. Science Immunology 10 (107); doi: 10.1126/sciimmunol.adn3080
