Summary: Researchers have discovered that daylight enhances the infection-fighting power of neutrophils, the most abundant white blood cells in the body. Using transparent zebrafish, scientists observed that these immune cells contain internal circadian clocks that are activated by light, boosting their bacterial-killing ability during the day.
This synchronization between daylight and immune response suggests an evolutionary adaptation to better defend against infections encountered during periods of activity. The findings could lead to new therapies that optimize immune function by targeting these cellular clocks.
Key Facts:
- Neutrophil Clocks: Neutrophils possess circadian clocks that respond to daylight.
- Peak Immunity Timing: Immune responses are stronger during daytime activity phases.
- Therapeutic Potential: Targeting neutrophil clocks may enhance treatment for infections and inflammation.
Source: University of Auckland
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.
About this circadian rhythm and immune system research news
Author: Gilbert Wong
Source: University of Auckland
Contact: Gilbert Wong – University of Auckland
Image: The image is credited to Neuroscience News
Original Research: Open access.
“A light-regulated circadian timer optimizes neutrophil bactericidal activity to boost daytime immunity” by Christopher Hall et al. Science Immunology
Abstract
A light-regulated circadian timer optimizes neutrophil bactericidal activity to boost daytime immunity
The immune response exhibits strong circadian rhythmicity, with enhanced bacterial clearance often synchronized with an organism’s active phase.
Despite providing the bulk of cellular antibacterial defense, the neutrophil clockwork is poorly understood.
Here, we used larval zebrafish to explore the role of clock genes in neutrophils during infection.
Per2 was required in neutrophils for reactive oxygen species (ROS) production and bacterial killing by enhancing infection-responsive expression of high-mobility group box 1a (hmgb1a).
The Cry binding domain of Per2 was required for regulation of neutrophil bactericidal activity, and neutrophils lacking Cry1a had elevated bactericidal activity and infection-responsive hmgb1a expression.
A conserved cis-regulatory element with BMAL1 and nuclear factor κB binding motifs gated infection-responsive hmgb1a expression to the light phase.
Mutagenesis of the BMAL1 motif in neutrophils blunted the priming effect of light on bactericidal activity and hmgb1a expression.
These findings identify a light-responsive cell-intrinsic timer that controls time-of-day variations in antibacterial activity.
