Kynurenine and tryptophan concentrations measured in the culture medium of DCs. iDCs were matured with CD40L + LPS without or with IFN-γ (± 1-methyl-tryptophan). iDCs of MS patients received MBP in addition to maturation factors. After 36 hours, the cell culture supernatants were harvested and the concentrations of kynurenine and tryptophan were measured by HPLC. The chromatograms (top rows of A and B) show the total free kynurenine (Kyn) and tryptophan (Trp) in cell-culture supernatants of DCs—without (left) and with (right) IFN-γ treatment—from one representative healthy donor (A) and MS patient (B). The mean ± SD concentrations of tryptophan and kynurenine of DCs from 7 healthy donors and 10 MS patients are shown in the bottom rows of panels A and B.