326 Tab. 1. M. Jenny et al.: Concentrations of tryptophan, kynurenine, neopterin and kyn/trp in the supernatant of unstimulated and phytohaemagglutinin (PHA; 10 μg/ml)- stimulated PBMC. Unstimulateda PHA [10 µg/ml]a Tryptophan [µmol/L 21.2 ± 1.6 2.6 ± 1.0** Kynurenine [µmol/L] 2.4 ± 0.6 9.9 ± 0.7** Kyn/trp [µmol/mmol] 119 ± 15 4658 ± 832** Neopterin [nmol/L] 4.7 ± 0.5 16.2 ± 1.8** a mean of 4 runs ± S.E.M. ** p <0.005, compared to unstimulated cells. The supernatants of unstimulated PBMC, cultivated for 48 hours under standard cultivation conditions, contained 21.1 ± 1.6 μmol/L tryptophan and 2.4 ± 0.6 μmol/L kynurenine resulting in a kynurenine to tryptophan ratio (kyn/trp) of 119 ± 15 µmol/mmol, as a measure of spontaneous IDO activity (Table 1). Upon treatment of PBMC with PHA [10 µg/ml] for 48 hours, tryptophan content decreased to 2.6 ± 1.0 μmol/L whereas kynurenine concentrations increased concomitantly to 9.9 ± 0.7 μmol/L, indicating an approximately 40-fold increase of IDO activity (4658 ± 832 µmol/mmol; Table 1). At the same time, neopterin concentrations raised from 4.7 ± 0.5 nmol/L in unstimulated cultures to 16.2 ± 1.8 nmol/L in PHA-stimulated PBMC cultures. Viability of cells was not affected by the treatment with 10 µg/ml PHA for 48 hours (data not shown). Fig. 1. A) Kynurenine to tryptophan ratio (Kyn/trp) and B) neopterin concentrations expressed as % of baseline in the supernatants of unstimulated (open circles) and phytohaemagglutinin (PHA)-stimulated PBMC (closed triangles) pretreated or not with increasing concentrations of Crinum latifolium leave extract for 48 hours. Results shown are the mean values ± S.E.M. of four independent experiments run in duplicates (*p <0.05). Treatment of PBMC with increasing concentrations of Crinum latifolium extracts for 48 hours, suppressed tryptophan degradation mediated by IDO activity (kyn/trp) in a dose- dependent manner in unstimulated- and PHA-stimulated cultures with IC50's of 241 ± 57 µg/ml (~1.2 µg/ml total alkaloids; 0.07 µg/ml crinamidine) and 92 ± 20 µg/ml (~0.5 µg/ml total alkaloids; 0.03 µg/ml crinamidine), respectively (Fig. 1A). At doses of 250 µg/ml, the Sci Pharm. 2011; 79: 323–335