Rationale : Low vitamin D levels hinders the ability of the macrophage to produce activated 1-25Dihydroxyvitamin at sites of inflammation. 1-25Dihydroxyvitamin D has important immunoregulatory functions including down-regulation of antigen-presenting cells such as dendritic cells. Under the influence of 1-25Dihydroxyvitamin D, these dendritic cells become tolerogenic ─ as opposed to immunogenic ─ and abrogate an immune response at early stages. Immunogenic dendritic cells play a key role in the development of autoimmune diseases such as Rheumatoid Arthritis (RA) by "presenting" self-antigens to the immune system. Vitamin D levels are frequently low in patients with RA. Restoring vitamin D availability to normal levels in patients with RA may induce improvement of disease manifestations through expansion of the tolerogenic dendritic cell subset.