CD8+ T cells are not necessary for 1α,25-dihydroxy-vitamin D3 to suppress experimental autoimmune encephalomyelitis in mice

In addition to its role in calcium and phosphorous homeostasis, 1alpha,25-dihydroxyvitamin D-3 [1,25-(OH)(2)D-3] appears to be a modulator of the immune system. Administration of 1,25-(OH)(2)D-3 prevents disease in several autoimmune animal models, including experimental autoimmune encephalomyelitis (EAE). The vitamin D receptor is believed to mediate this activity. Among cells of the immune system, CD8(+) T cells have the highest levels of the vitamin D receptor. Because CD8(+) T cells have been implicated as both suppressors and effectors of the inflammation associated with multiple sclerosis and EAE, we examined the question of whether the 1,25-(OH)(2)D-3 suppression of EAE occurs through a CD8(+) T cell-dependent mechanism. To test this hypothesis, mice that are homozygous knockouts for the alpha chain of the CD8 receptor and have been characterized as lacking functional CD8(+) T cells (CD8+ -/-) were provided 1,25(OH)(2)D-3 in their diet before EAE induction. Although CD8(+) -/- mice fed the same diet lacking 1,25(OH)(2)D-3 have a high incidence of EAE, EAE did not occur in CD8(+) -/- mice fed the diet containing 1,25-(OH)(2)D-3. We conclude that CD8(+) T cells neither are needed nor do they play a role in the prevention of EAE by 1,25-(OH)(2)D-3.