DPP4 and major depressive disorder: In particular, in one of our studies we found that the percentage of circulating CD4+CD26+CD161+CD196+ Th17-cells and production of IL-17 and IFN-γ by anti-CD3/anti-CD28-stimulated PBMCs was higher in patients with relapsing-remitting MS and depression (n=20) compared to patients without depression (n=25) or to the control group (healthy subjects, n=20).