Inhibitory effect of mesenchymal stem cells on lymphocyte proliferation

We investigated the mechanism underlying the inhibitory effect of rat mesenchymal stem cells (MSCs) on non‐specific mitogen‐stimulated lymphocytes (LCs) and lymphoblasts (LBs). We used MSCs of passages 2–8 prepared from Sprague–Dawley (SD) rats. LCs were isolated from the spleens of SD rats. Mixed LCs reactions of mitomycin C‐treated MSCs with concanavalin A (ConA)‐stimulated LCs or LBs were performed, and the proliferation inhibition effect was tested by MTS assay. The cytotoxicity of MSCs against naïve and ConA‐stimulated LBs was detected, after co‐culturing for 24 h, by lactate dehydrogenase release assay. The rate of apoptosis of ConA‐stimulated LBs was measured by flow cytometry after incubation with MSCs for 9 h in the ratio 10:1. The MSCs were treated with Fas ligand (FasL), transforming growth factor (TGF)‐β, and interleukin (IL)‐10 blocking antibodies and co‐cultured with ConA‐stimulated LBs to observe the apoptosis and growth inhibitory effect. The main outcomes were bone marrow‐derived adherent CD29⁺, CD44⁺, CD45^?, CD54⁺, CD95⁺, and SH‐2⁺ MSCs. FasL, TGF‐β, and IL‐10 production by MSCs were visualized by immunocytochemical analysis. MSCs exhibited a dose‐dependent growth inhibitory effect on ConA‐stimulated LCs and LBs. When treated with anti‐FasL and anti‐IL‐10 blocking antibodies, the inhibitory effect of MSCs on LBs proliferation, and the effect of apoptosis induction on LBs decreased. Anti‐TGF‐β blocking antibody treatment did not significantly influence MSCs. Therefore, the inhibitory effects of MSCs against activated LBs were significantly stronger than that against naïve LCs. FasL and IL‐10, rather than TGF‐β, play important roles in the immunosuppressive effects of MSCs. Copyright © 2008 John Wiley & Sons, Ltd.