Immunomodulatory effects of vitamin D in peripheral blood monocyte-derived macrophages from patients with rheumatoid arthritis

1,25-Dihydroxyvitamin D (1,25(OH)₂D₃), the active form of vitamin D, modulates both innate and adaptive immune responses. Emerging epidemiological data has also demonstrated disease-modifying and immunomodulatory effects of vitamin D in a wide range of human autoimmune diseases, including rheumatoid arthritis (RA). To evaluate in vitro effects of 1,25(OH) ₂D₃ in primary cultures of peripheral blood monocyte-derived macrophages of RA patients, monocyte/macrophages, isolated from peripheral blood mononuclear cells of RA patients and healthy subjects by exploiting their ability to adhere to plastic, were treated with increasing concentrations of 1,25(OH)₂D₃ for 48 h. TNF-α, IL-1 α, IL-1β, IL-6 and RANKL production was determined by ELISA and nitric oxide (NO) release using the Griess method. Immunocytochemistry analysis was also performed to evaluate alterations in transmembrane TNF-α expression after 1,25(OH) ₂D₃ treatment. A significant dose-dependent decrease in TNF-α and RANKL production by cultured RA macrophages after 1,25(OH)₂D₃ treatment was found, whereas a significant reduction in normal cells was observed only at higher concentrations. IL-1 α, IL-1β and IL-6 levels were reduced by 1,25(OH) ₂D₃ at higher concentrations in all cell populations. TNF-α immunostaining was less intense in treated cells compared with untreated. 1,25(OH) ₂D₃ significantly reduced NO levels regardless of the concentration used. Vitamin D downregulated proinflammatory mediators in monocyte-derived macrophages, and RA cells appeared more sensitive than normal cells. These effects further provide a rationale for the therapeutic value of vitamin D supplementation in the treatment for RA.