Health. Daylight: How does it strengthen our immune system?

Is our immune system more efficient during daylight hours? This is the question that a New Zealand team is investigating.

To answer this question, scientists focused on the role of neutrophils, the most abundant immune cells in our bodies. This type of white blood cell is our first line of defense against infection, moving quickly to infected sites to eliminate invasive bacteria.

Zebrafish as a model

The researchers used zebrafish, a small freshwater fish, as a model organism because its genetic makeup is similar to ours. Furthermore, it can be bred to have a transparent body, making it easier to observe biological processes in real time.

"In previous studies, we observed that immune responses peaked in the morning, during the fish's first active phase," said Professor Christopher Hall of the University of Auckland's Department of Molecular Medicine and Pathology. "This is an evolutionary response. During the daytime, the body is more likely to encounter bacterial infections and is therefore more active."

However, scientists wanted to discover how the immune response synchronizes with daylight. They observed that neutrophils have their own circadian clock (biological clock), which alerts them to the presence of daylight and stimulates their ability to kill bacteria.

According to the authors, "most of our cells are equipped with circadian clocks that tell them what time it is in the outside world, in order to regulate the body's activities. Light is the most important factor in resetting these biological clocks."

"Since neutrophils are the first immune cells to be recruited to sites of inflammation, this discovery paves the way for the development of drugs to enhance their ability to fight infections," concludes Christopher Hall.