http://scienmag.com/sunlight-offers-surprise-benefit-it-energizes-infection-fighting-t-cells/
"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."