ABSTRACT
BACKGROUND: Mesenchymal stem cells (MSC) can be defined by their extensive in vitro self renewal capacity and multi-lineage differentiation potentiality. These cells possess in vitro immunosuppressive properties that appear not to be major histocompatibility complex (MHC) restricted. This study evaluated the immune suppressive effect of mouse MSC on mixed lymphocyte reaction (MLR), and the mechanisms were investigated. METHODS: MSC were obtained from BALB/c bone marrow and cultured in low-glucose DMEM media. The expression of surface antigens and cell cycle were analyzed by flow cytometry. The MSC-induced suppression was assessed by MLR and transwell culture. RESULTS: The BALB/c MSC constitutively expressed MHC class I and CD54 (ICAM-1) antigens but were negative for MHC class II, CD40, CD80 (B7-1) and CD106 (VCAM-1) antigens. MSC suppressed allogeneic C57BL/6 T lymphocytes proliferation by adding them to MLR in which C3H spleen cells were used as a stimulator. This inhibition was dependent on the dose of BALB/c MSC but independent of MHC. C57BL/6 T lymphocytes proliferation was still inhibited when BALB/c MSC were added in culture 3 days after starting of MLR. When MSC were separated from C57BL/6 T cells by using the transwell membrane, the suppression of immune response wasn't observed, which suggested that the suppressive effect was dependent on cell-cell contact between BALB/c MSC and C57BL/6 T cells. When C57BL/6 T lymphocytes were cultured with MSC, the percentage of C57BL/6 T cells in G0 phase increased from 51.8+/-7.66% to 77.2+/-7.39% compared with the case that only C57BL/6 T cells were cultured. When the C57BL/6 T cells were cultured with C3H spleen cells, most of C57BL/6 T cells were in G2/M (96.38+/-3.33%). But by the addition of MSC to MLR, the percentage of T cells in G2/M decreased to 33.0+/-9.66% while that of T cells in G0 increased to 66.2+/-7.46%. CONCLUSIONS: We concluded that the cell cycle of responder T lymphocytes in MLR is arrested at G0 phase by MSC.