STANFORD, Calif., Feb. 5 U.S. medical scientists say they have discovered immune cells travel to protect the outer layers of the skin in response to sunlight-induced vitamin D.Eugene Butcher and colleagues at the Stanford University School of Medicine say the immune cells express enzymes that convert an inactive form of vitamin D -- which is synthesized by skin cells upon sun exposure -- to an active form that triggers expression of certain homing receptors on the surface of effector T cells. Those receptors, say the researchers, can draw T cells to the skin's surface where they participate in immune surveillance and maintain barrier function.The study suggests brief periods in the sun to generate the precursor form of active vitamin D might be beneficial by eliciting immune cells to skin tissues where they can ward off potential opportunistic pathogens and help repair ultraviolet light-induced damage.The research is detailed in the March issue of Nature Immunology.Copyright 2007 by UPI
