Fig. 4

The IFN-γ and poly(I:C)-primed MSC expanded Treg cells in an IDO1-dependent manner. Mice with the DSS-induced colitis were sacrificed on day 9 to harvest the spleen, mLN, and colon tissue. Representative data of two independent experiments are presented (normal, n = 3; other groups, n = 4). a Treg (CD25⁺Foxp3⁺CD4⁺) proportions to CD4⁺ T cells in the spleen and mLN significantly increased in the primed MSC group than in the DSS control group. Difference of the Treg proportion between the primed MSC and the unstimulated MSC group was evident only in the spleen. b The colonic mRNA expression of Treg (Foxp3) markedly increased only in the primed MSC group. c T cells were negatively selected from splenocytes of B6 mice and co-cultured with the unstimulated or primed MSC in the presence of anti-CD3/CD28 antibodies. The primed MSCs increased the proportion of Treg (CD25⁺Foxp3⁺CD4⁺) to CD4⁺ T cells more effectively than the unstimulated MSC did. d A competitive IDO1 inhibitor, L-1MT, reversed the Treg expansion which was induced by the primed MSC (*p < 0.05, **p < 0.01, ***p < 0.001)