CD4 and autoimmune disease: The studies in animals and humans implicating calcitriol as a positive regulator of the Tnfsf11a and Tnfrsf11a genes and cutaneous FoxP3+ pTreg cell induction suggest that during periods of light starvation, phototherapy may be a particularly efficient method of influencing the emergence of an autoimmune disease phenotype by increasing CD4+CD25+FoxP3+ Treg cell development and suppressive function.