Sunlight Offers Surprise Benefit — It Energizes Infection Fighting T Cells

“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,” says the study’s senior investigator, Gerard Ahern, PhD, associate professor in the Georgetown’s Department of Pharmacology and Physiology. “Some of the roles attributed to vitamin D on immunity may be due to this new mechanism.”

They specifically found that low levels of blue light, found in sun rays, makes T cells move faster — marking the first reported human cell responding to sunlight by speeding its pace.

“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,” Ahern says. “This study shows that sunlight directly activates key immune cells by increasing their movement.”

Ahern also added that while production of vitamin D required UV light, which can promote skin cancer and melanoma, blue light from the sun, as well as from special lamps, is safer.

And while the human and T cells they studied in the laboratory were not specifically skin T cells — they were isolated from mouse cell culture and from human blood — the skin has a large share of T cells in humans, he says, approximately twice the number circulating in the blood.

“We know that blue light can reach the dermis, the second layer of the skin, and that those T cells can move throughout the body,” he says.

The researchers further decoded how blue light makes T cells move more by tracing the molecular pathway activated by the light.

What drove the motility response in T cells was synthesis of hydrogen peroxide, which then activated a signaling pathway that increases T cell movement. Hydrogen peroxide is a compound that white blood cells release when they sense an infection in order to kill bacteria and to “call” T cells and other immune cells to mount an immune response.

“We found that sunlight makes hydrogen peroxide in T cells, which makes the cells move. And we know that an immune response also uses hydrogen peroxide to make T cells move to the damage,” Ahern says. “This all fits together.”

Ahern says there is much work to do to understand the impact of these findings, but he suggests that if blue light T cell activation has only beneficial responses, it might make sense to offer patients blue light therapy to boost their immunity.

Study co-authors include lead investigator Thieu X. Phan, PhD, Barbara Jaruga, PhD, Sandeep C. Pingle, PhD, and Bandyopadhyay, PhD, all from the Georgetown University Medical Center’s Department of Pharmacology and Physiology.

The authors report having no personal financial interests related to the study.

The study was supported by a pilot grant from the National Multiple Sclerosis Society.

About Georgetown University Medical CenterGeorgetown University Medical Center (GUMC) is an internationally recognized academic medical center with a three-part mission of research, teaching and patient care (through MedStar Health). GUMC’s mission is carried out with a strong emphasis on public service and a dedication to the Catholic, Jesuit principle of cura personalis -- or "care of the whole person." The Medical Center includes the School of Medicine and the School of Nursing & Health Studies, both nationally ranked; Georgetown Lombardi Comprehensive Cancer Center, designated as a comprehensive cancer center by the National Cancer Institute; and the Biomedical Graduate Research Organization, which accounts for the majority of externally funded research at GUMC including a Clinical and Translational Science Award from the National Institutes of Health. Connect with GUMC on Facebook (Facebook.com/GUMCUpdate), Twitter (@gumedcenter) and Instagram (@gumedcenter).