Objective To investigate whether human bone marrow mesenchymal stem cells (hBC-MSCs) have the immune-suppression ability on the proliferation of peripheral blood mononuclear cells (PBMCs) and their pro-inflammatory cytokine production in rats,to explore what kinds of human cytokines are required for the induction of hBM-MSCs to become immune-suppressive,and to observe the effect of intravenous delivery of hBM-MSCs on tumor necrosis factor (TNF)-α transcription and expression in the core infarct areas of rats after cerebral ischemia.Methods The fetal-originated hBC-MSCs and rat PBMCs were extracted;the rat PBMCs were activated by adding 10 μg/mL concanavalin A (ConA).(1) The first experiment was divided into hBM-MSCs+PBMCs group,hBM-MSCs+PBMCs+ConA group,PBMCs group and hBM-MSCs group;CCK-8 assay was employed to detect the proliferation of these cells.(2) The second experiment was divided into hBM-MSCs+PBMCs+ConA group,PBMCs+ConA group;ELISA was used to detect the TNF-α,interferon-γ (IFN-γ) and intedeukin (IL)-10 expressions.(3) The third experiment was divided into hBM-MSCs+PBMCs (IFN-γ+IL-1α) group,hBM-MSCs+PBMCs (IFN-γ+IL-1β) group,hBM-MSCs+PBMCs (IFN-γ+TNF-α) group and hBM-MSCs+PBMCs group;CCK-8 assay was used to detect the proliferation of these cells.(4) Thirty SD rats were randomly divided sham-operated group,control group (giving normal saline after ischemia) and hBM-MSCs group (giving hBM-MSCs after ischemia,n=10);on the third d of ischemia,the TNF-α mRNA and protein expressions at the infarct areas was detected by real time PCR and Western blotting,respectively.Results (1) The optical density (OD) in the hBM-MSCs+PBMCs group was significantly increased as compared with that in the PBMCs group and hBM-MSCs group (P＜0.05);OD in the hBM-MSCs+PBMCs group was significantly increased as compared with that in the hBM-MSCs+PBMCs+ConA group (P＜0.05).(2) The TNF-α,IFN-γand IL-10 levels in the PBMCs+ConA group were (1030±196) pg/mL,(2880±250) pg/mL and (330±45) pg/mL;the TNF-α and IFN-γlevels in hBM-MSCs+PBMCs+ConA group were (160±10) pg/mL and (240±55) pg/mL,which were significantly lower than those in the PBMCs+ConA group (P＜0.05);the IL-10 level in hBM-MSCs+PBMCs+ConA group was (750±110) pg/mL,which was significantly higher than that in the PBMCs+ConA group (P＜0.05).(3) The OD in the hBM-MSCs+PBMCs(IFN-γ+IL-1α)group,hBM-MSCs+PBMCs (IFN-γ+IL-1 β) group and hBM-MSCs+PBMCs (IFN-γ+TNF-α) group was significantly decreased as compared with that in the hBM-MSCs+PBMCs group (P＜0.05).(4) The TNF-α mRNA expression in the sham-operated group,control group and hBM-MSCs group was 0.490±0.128,2.369±0.788 and 1.002±0.408;the TNF-α protein expression in the sham-operated group,control group and hBM-MSCs group was 0.144±0.028,0.314±0.029,0.240±0.029;the TNF-α protein and mRNA expressions in the hBM-MSCs group were significantly decreased as compared with those in the control group (P＜0.05).Conclusions The allogeneic transplantation of hBC-MSCs is competent in suppressing the inflammation of rats in vitro and in vivo.Furthermore,this immune-suppression ability is not innate,but cytokine stimulation dependent.The immune-suppression ability of hBM-MSCs on rat PBMCs are at least partly responsible for the therapeutic effect of hBM-MSCs transplantation into the rat models,such as ischemia stroke.