14 October 2025

Recent study reveals how daylight powers our defenses

A study, led by scientists at Waipapa Taumata Rau, University of Auckland, has uncovered how our immune system synchronizes with daylight to fight infections more effectively.

The Core Finding: Neutrophils (our most abundant infection-fighting white blood cells) have their own internal circadian clocks that make them significantly more effective at killing bacteria during daytime hours when we’re active. This likely represents an evolutionary adaptation that helps protect diurnal organisms when they’re most at risk of encountering pathogens.

The Research Approach: Using transparent zebrafish larvae as a model allowed the researchers to actually film neutrophils in action within living animals at different times of day. This direct observation method overcame the challenge of studying human neutrophils, which are notoriously difficult to work with in the lab due to their short lifespan.

The Mechanism: When the researchers genetically “broke” the neutrophils’ circadian clocks (like removing cogs from a clock), the cells lost their enhanced daytime bacteria-killing ability. This proved that neutrophils possess light-regulated internal timing systems that act like cellular alarm clocks, alerting them to ramp up their antibacterial activity during daylight.

Clinical Implications: This discovery opens up entirely new therapeutic possibilities. Since neutrophils are the first responders to inflammation and infection, drugs that target their circadian clocks could potentially treat a wide range of inflammatory conditions by timing when these cells are most or least active.

The collaboration between the Hall laboratory and the Chronobiology Research Group demonstrates how interdisciplinary research can uncover fundamental biological mechanisms we didn’t even know existed.

Go to the article on Science Immunology: A light-regulated circadian timer optimizes neutrophil bactericidal activity to boost daytime immunity