WASHINGTON (dpa-AFX) - A new study by scientists at the University of Auckland has found that sunlight can help the body's immune system fight infections more effectively.
In the study, the researchers focused on neutrophils, a type of white blood cell that's very common in our body. These cells are the first to respond to infections and work by attacking and killing harmful bacteria.
To do their research, the scientists used zebrafish, a small fish with genes similar to humans. These fish can also be made transparent, which helped scientists watch what's happening inside their bodies in real time.
The study, published in Science Immunology, discovered that neutrophils have an internal body clock, called a circadian clock, that helps them tell what time of day it is. This clock seems to boost their bacteria-fighting ability during daylight hours.
Notably, most cells in our body use these internal clocks to keep track of time and manage the body's functions. Light plays a key role in setting these clocks.
The team found that immune responses were strongest during the day, when both zebrafish and humans are most active, which is a possible evolutionary advantage, since we're more likely to get exposed to bacteria when we're active.
To figure out why immune activity peaked during the day, the scientists filmed the neutrophils fighting bacteria at different times and found that the cells were better at killing bacteria during the day than at night.
Next, they turned off the neutrophils' internal clocks by removing key parts of the clock's genetic mechanism. When they did this, the cells lost their ability to respond to light and didn't fight bacteria as well. This showed that neutrophils have their own built-in clock that responds to light, boosting their bacteria-killing power during the day.
Following this conclusion, the researchers now want to find out exactly how neutrophils sense light, and if human immune cells work the same way.
'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,' noted lead researcher Associate Professor Christopher Hall. 'This finding paves the way for the development of drugs that target the circadian clock in neutrophils to boost their ability to fight infections.'
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