Maturation of human dendritic cells as sulfasalazine target

Aim. Sulfasalazine, a nonsteroidal anti-inflammatory drug, is effective in treating some autoimmune diseases, but its mechanism of action is unclear. To determine whether dendritic cells could be a possible target of the drug, we studied the effects of sulfasalazine and its metabolites, aminosalicylate and sulfapyridine, on in vitro maturation (terminal differentiation) of human myeloid dendritic cells. Methods. We prepared immature dendritic cells by incubating CD14-positive cells in the presence of granulocyte-macrophage colony-stimulating factor and interleukin (IL)-4. The cells were matured by addition of tumor necrosis factor (TNF)-a, IL-1β, and prostaglandin E2 in the presence of sulfasalazine or its metabolites - aminosalicylate and sulfapyridine, or their combinations. We quantified the effect of drugs on the dendritic cell characteristics, such as stimulation of autologous and allogeneic pan-T cell proliferation, surface marker phenotype, IL-12 p40 subunit secretion, and activation of nuclear transcription factor (NF)-κB. Results. Dendritic cells treated with sulfasalazine (1.25 μmol/L or 2.5 μmol/L) could not stimulate T cells (p < 0.028, two-sided paired t-test). In distinction to drug-free maturing dendritic cells, 2.5 μmol/L sulfasalazine upregulated the levels of CD14 and CD68 and downregulated the levels of CD40, CD80, and CD83 (for all CD markers, p < 0.03 for difference between measurements in the absence and the presence of sulfasalazine). From concentration-dependent changes in CD83 expression, we found an apparent ID50 ≅ 1.5 μmol/L sulfasalazine. The apparent ID₅₀ value for aminosalicylate-inhibited maturation was 4 μmol/L. Sulfapyridine had no effect. At 1.25 μmol/L, sulfasalazine largely inhibited NF-κB activation in dendritic cells. Conclusion. Maturing human dendritic cells are hundred-fold more sensitive to sulfasalazine than T cells and NK cells and the most sensitive human cells described so far. Thus, dendritic cell maturation is an important target of sulfasalazine. Because of the role of dendritic cells in (auto)immunity, inhibition of their maturation might provide a target for further optimization of sulfasalazine therapy.