Figure 4.

Lactate drives human pDCs to generate FoxP3⁺ T regulatory cells. (A,B) Autologous CD45RA⁺CD4⁺ T cells were co-cultured with untreated pDCs, K⁺-Lac treated pDCs or lactate+ARC treated pDCs for 5 days before being intracellularly stained and acquired on a flow cytometer. n = 6 from 2 independent experiments and one-tailed Wilcoxon matched-pairs signed rank test was done. (C) Cell culture supernatants from pDC-T cell co-cultures, where pDCs were pre-treated as indicated, were subjected to acetonitrile extraction followed by LC-MS/MS to quantify the concentration of tryptophan and kynurenine in them. n = 8 from 3 independent experiments and two-tailed Wilcoxon matched-pairs signed rank test was done. (D) The ratio of kynurenine: tryptophan in the culture supernatants was correlated with the percentage of FoxP3⁺ cells in the co-cultures by Spearman's correlation (N = 4 in duplicate) (^*p < 0.05, ^**p < 0.005).