Daylight stimulates our white blood cells and strengthens immunity.

Recent studies show that our immune cells, specifically neutrophils, function more effectively during the day. It turns out that they have an internal biological clock that responds to sunlight. This discovery could have huge implications for treating inflammation and infections.

A team of scientists from the University of Auckland has proven that daylight strengthens the functioning of our immune system. The key role here is played by the circadian rhythm, or our biological clock. Disturbances of this rhythm - for example, due to shift work or going to bed late - can weaken immunity. This phenomenon, called "social jet lag", is associated with greater susceptibility to infections.

To understand how circadian rhythms affect the immune system, researchers turned to an unusual helper: the zebrafish, a small, transparent freshwater fish. The larvae of this fish have an immune system similar to that of humans, and their transparency allows their cells to be closely observed under a microscope.

The main hero of the study were neutrophils - the most numerous white blood cells in our body, responsible for rapid response to bacterial infections. Scientists observed that these cells are most active and effective during the day, when the body is exposed to daylight.

As Professor Chris Hall says:

To see how neutrophils “know” when to act, researchers genetically modified the cells, removing components of their biological clock. They found that without these mechanisms, their ability to kill bacteria decreases.

The bottom line? Neutrophils have their own internal clock that syncs with daylight – it acts like a biological alarm clock that “tells” cells it’s time to fight infection.

Scientists now want to test whether human neutrophils work similarly, and whether this mechanism works only against specific bacteria or in response to a variety of threats, including viruses. The researchers see potential in this for creating new drugs that regulate the biological clock of immune cells.

The research was conducted by PhD students Lucia Du and Pramuka Keerthisinghe as part of a collaboration between Hall’s lab and the Chronobiology Research Group, led by Guy Warman and James Cheeseman.