Study Reveals Why Your Immune System Works Better in Daylight

A new study has revealed that the immune system is regulated by a circadian clock and becomes more active during daylight hours. The research, published in Science Immunology, shows that neutrophils—the body’s most abundant white blood cells—are influenced by light, which enhances their ability to fight infections.

The study, led by Associate Professor Christopher Hall from the Department of Molecular Medicine and Pathology, used zebrafish as a model organism due to their genetic similarities to humans and their transparent bodies, which allow real-time observation of biological processes.

Researchers discovered that neutrophils possess their own circadian clock, which senses daytime and boosts their antibacterial activity. This internal timing mechanism is influenced primarily by light, which is known to be the strongest factor in resetting circadian rhythms across most cells in the body.

"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," says Hall.

The team believes that manipulating the circadian clock in neutrophils could lead to new treatments for infectious and inflammatory conditions. “This finding paves the way for development of drugs that target the circadian clock in neutrophils to boost their ability to fight infections,” Hall adds.

Reference: Lucia Yi Du, Pramuk Keerthisinghe, Leah Rolland, Yih Jian Sung, Hannah Darroch, Tanja Linnerz, Elina Ashimbayeva, Matthew J. Grant, Purvi M. Kakadia, Annasuya Ramachandran, Alexander Tups, Herman P. Spaink, Stefan K. Bohlander, James Cheeseman, Philip S. Crosier, Jonathan W. Astin, Guy Warman, Christopher J. Hall. A light-regulated circadian timer optimizes neutrophil bactericidal activity to boost daytime immunity. Science Immunology, 2025; 10 (107) DOI: 10.1126/sciimmunol.adn3080