“Each day, Apollo’s fiery chariot makes its way across the sky, bringing life-giving light to the planet. For the ancient Greeks and Romans, Apollo was the god of medicine and healing as well as of sun and light—but Apollo could bring sickness as well as cure. Today’s scientists have come to a similarly dichotomous recognition that exposure to the ultraviolet radiation in sunlight has both beneficial and deleterious effects on human health.”
Indeed, we’re all familiar with the deleterious effects of UVB wavelengths, those that cause sunburns and induce DNA damage, potentially resulting in skin cancers. And we’re also familiar with a major benefit of sunlight—the ability to kick off the chemical and metabolic chain reaction that produces vitamin D, which plays a major role in the immune response.
Less known is the ability of sunlight to energize T cells, an essential component of the immune system. T cells produced during the adaptive immune response access body surfaces, including the skin, to protect against invading pathogens. It is in the skin that T cells could be exposed to sunlight.
The finding of sunlight’s effects on T cells is relatively recent—it was published a few months ago in the journal Scientific Reports. The study (Intrinsic Photosensitivity Enhances Motility of T Lymphocytes), which was carried out in mice and humans, shows that low levels of blue light, found in sun rays, increase the motility of T cells. In other words, it makes T cells move faster.
Gerard Ahern, senior author of the study, said in a press release: “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. Some of the roles attributed to vitamin D on immunity may be due to this new mechanism. 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.”
The increased T cell motility is driven by a signaling pathway activated by the synthesis of hydrogen peroxide. Hydrogen peroxide is a compound released by white blood to kill invading pathogens and mobilize other immune cells, including T cells.
The researcher conclude that T cells are a new type of photoreceptive cell and their photosensitivity may contribute to the effects of sunlight on immune function.
Ahern said that there is much work to do to understand the impact of these findings. However, 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.