Monocyte-derived dendritic cells release neopterin.

Increased neopterin concentrations in body fluids are found in diseases associated with activated, cell-mediated immunity including infections, autoimmune diseases, and certain malignancies. Monocytes/macrophages are known to secrete large amounts of neopterin upon stimulation with interferon-gamma (IFN-gamma). Ontogenetically, the major part of dendritic cells (DC) belongs to the myeloid lineage. Therefore, we investigated whether cultured monocyte-derived DC can elaborate neopterin. Cells were treated with cytokines in the presence or absence of monocyte-conditioned medium as a maturation stimulus. DC secreted an average 3.5 nmol/l neopterin. In response to IFN-gamma, cells significantly increased their output of neopterin. In distinction to monocytes/macrophages, neopterin production in DC was highly sensitive to IFN-alpha and IFN-beta. Further, lipopolysaccharides (LPS) enhanced neopterin synthesis, whereas tumor necrosis factor alpha, interleukin (IL)-1beta, IL-2, IL-10, and IL-18 were ineffective. Simultaneously, tryptophan degradation by induction of indoleamine (2,3)-dioxygenase (IDO) was tested in stimulated cells. Our results showed that IFN-gamma as well as LPS are inducers of IDO in DC.