“We all know sunlight provides vitamin D, which is suggested to have an impact on immunity, among other things. But what we found is a completely separate role of sunlight on immunity,” said Gerard Ahern, Associate Professor at the Georgetown University in the US.
“Some of the roles attributed to vitamin D on immunity may be due to this new mechanism,” Ahern added.
The findings showed that the skin, which is the body’s largest organ has a large share of T cells — approximately twice the number circulating in the blood – stays alert to the many microbes that can nest there.
While production of vitamin D requires ultra violet (UV) light – known to promote skin cancer and melanoma, the low levels of blue light found in the sun’s rays is safer and helps makes T cells move faster.
This blue light, which can reach the dermis – the second layer of the skin – enables the T cells to move throughout the body, the researchers stated.
“T cells, whether they are helper or killer, need to move to do their work, which is to get to the site of an infection and orchestrate a response. This study shows that sunlight directly activates key immune cells by increasing their movement,” Ahern said.
In addition, the researchers also found that the synthesis of hydrogen peroxide – a compound that white blood cells release when they sense an infection in order to kill bacteria and mount an immune response — activates a signalling pathway to increase T cell movement.