Moreover, another study analyzed the number and proportion of T cells in the spleens and MLNs of mice with colitis after treatment with hucMSCs and found that hucMSCs inhibit apoptosis, promote Type 1 regulatory T (Tr1) cell proliferation, increase the proportion of Tr1 cells, and enhance the immunosuppressive function of Tr1 based on their paracrine indoleamine-2,3- dioxygenase (IDO), and when IDO is blocked, MSCs are unable to upregulate Tr1 cells [104]. This evidence concerns the gene IDO1 and colitis.