Fig. 6

Effects of 5-hydroxytryptophan (5-HTP) on the production of serotonin and kynurenine in the mice with collagen-induced arthritis (CIA). Serum levels of serotonin and kynurenine in the CIA mice from groups 1, 3 and 6 were measured by ELISA. a Serum levels of serotonin and kynurenine (mean ± standard error) in the CIA mice. *Significant compared with group 1. (–) same-aged DBA/1 mice. The grouping was as described in Fig. 3a. Multiple comparisons were performed using the Kruskal–Wallis test, if significant (p <0.05), then the Duncan test was used to find out which pairs were different. b Correlations between the levels of serotonin, kynurenine and arthritis scores in the CIA mice. Statistical analysis was performed using Spearman’s rank correlation. c Splenocytes were treated with 5-HTP alone or in combination with kynurenine, fluoxetine or NSD-1015, and then stimulated with anti-CD3 plus anti-CD28 Abs. Cytokine levels (mean ± SD) of TNFα and IFNγ in culture supernatants were measured N.D. undetectable. a Significant compared with control group/column one. b Significant compared with 5-HTP (20 μg/ml). c Significant compared with 5-HTP (50 μg/ml). The Mann–Whitney test was used to analyze the effects of kynurenine (Kynu), fluoxetine (Fluo) and NSD-1015 on the cytokine production in 5-HTP-treated splenocytes