BACKGROUND: Microglia are very sensitive to environmental changes, often becoming activated by pathological conditions. Activated microglia can exert a dual role in injury and repair in various diseases of the central nervous system, including cerebral ischemia, Parkinson’s disease, and Alzheimer’s disease. OBJECTIVE: An immortal microglial cell line, BV2, was treated with varying concentrations of lipopolysaccharide (LPS) to induce a pathological situation. Supernatant was harvested and incubated with bone marrow mesenchymal stem cells and, concomitantly, bone marrow mesenchymal stem cell differentiation was observed. DESIGN: A controlled observation, in vitro experiment. SETTING: Department of Neurology, First Affiliated Hospital of China Medical University. MATERIALS: Five male 2–3-week-old Sprague Dawley rats were purchased from Animal Laboratory Center of China Medical University and included in this study. The protocol was performed in accordance with ethical guidelines for the use and care of animals. The microglial cell line BV2 was produced by Cell Research Institute of Chinese Academy of Sciences. LPS was produced by Sigma Company, USA. METHODS: This study was performed in the Central Laboratory of China Medical University from September 2006 to March 2007. Rat femoral and tibial bone marrow was collected for separation and primary culture of bone marrow mesenchymal stem cells. Bone marrow mesenchymal stem cell cultures were divided into 5 groups: control group, non-activated group, as well as low-, medium-, and high-dose LPS groups. In the control group, bone marrow mesenchymal stem cells were cultured with Dulbecco’s modified Eagle’s medium (DMEM) supplemented with fetal bovine serum (volume fraction 0.1). In the non-activated group, bone marrow mesenchymal stem cells were incubated with non-activated BV2 supernatant. In the low-, medium-, and high-dose LPS groups, bone marrow mesenchymal stem cells were incubated with LPS (0.01, 0.1 and 1 μg/L, respectively)-activated BV2 supernatant. MAIN OUTCOME MEASURES: Expression of glial fibrillary acidic protein (GFAP) and neuron-specific enolase (NSE) in bone marrow mesenchymal stem cells was detected by immunofluorescence staining. RESULTS: GFAP-positive cells were detected in each group; however, the greatest number were found in the high-dose LPS group. The number of GFAP-positive cells was significantly greater in the high- and medium-dose groups, compared to the control, non-activated, and low-dose LPS groups (P < 0.05). However, there was no significant difference between the medium- and high-dose LPS groups (P > 0.05). NSE-positive cells were also detected in each group. However, there was no significant difference between any two groups (P > 0.05). CONCLUSION: Microglia, when activated to some ertent, could induce neuroglial cell differentiation from bone marrow mesenchymal stem cells; however, they did not exhibit the capacity to markedly promote neuronal cell differentiation. When microglia are activated, the capacity to induce bone marrow mesenchymal stem cell differentiation reaches a peak level, but is not increased with greater activation rates. BACKGROUND: Microglia are very sensitive to environmental changes, often becoming activated by pathological conditions. Activated microglia can exert a dual role in injury and repair in various diseases of the central nervous system, including cerebral ischemia, Parkinson’s disease, and Alzheimer’s disease. OBJECTIVE: An immortal microglial cell line, BV2, was treated with varying concentrations of lipopolysaccharide (LPS) to induce a pathological situation. Supernatant was harvested and incubated with bone marrow mesenchymal stem cells and, concomitantly, bone marrow mesenchymal stem cell differentiation was observed. A controlled observation, in vitro experiment. SETTING: Department of Neurology, First Affiliated Hospital of China Medical University. MATERIALS: Five male 2-3-week-old Sprague Dawley rats were purchased from Animal Laboratory Center of China Medical University and included in this study. The protocol was performed in accordance with ethical guidelines for the use and care of animals. The microglial cell line BV2 was produced by the Cell Research Institute of Chinese Academy of Sciences. LPS was produced by Sigma Company, USA. METHODS: This study was performed in the Central Laboratory of China Medical University from September 2006 to March 2007. Rat femoral and tibial bone marrow was collected for separation and primary culture of bone marrow mesenchymal stem cells. Bone marrow mesenchymal stem cell cultures were divided into 5 groups: control group, non-activated group, as well as low-, medium-, and high-dose LPS groups. In the control group, bone marrow mesenchymal stem cells were cultured with Dulbecco’s modified Eagle’s medium (DMEM) supplemented with fetal bovine serum (volume fraction 0.1). In the non-activated group, bone marrow mesenchymal stem cells were incubated with non-activated BV2 supernatant. In the low-, medium-, and high-dose LPS groups, bone marrow mesenchymal stem cells were incubated with LPS (0.01, 0.1 and 1 μg / L, respectiMAIN OUTCOME MEASURES: Expression of glial fibrillary acidic protein (GFAP) and neuron-specific enolase (NSE) in bone marrow mesenchymal stem cells was detected by immunofluorescence staining. RESULTS: GFAP-positive cells were detected in each The number of GFAP-positive cells was significantly greater in the high- and medium-dose groups, compared to the control, non-activated, and low-dose However, there was no significant difference between the medium- and high-dose LPS groups (P> 0.05). However, there was no significant difference between the medium- and high-dose LPS groups any two groups (P> 0.05). CONCLUSION: Microglia, when activated to some ertent, could induce neuroglial cell differentiation from bone marrow mesenchymal stem cells; however, they did not exhibit the capacity to markedly promote neuronal cell differentiation. When m icroglia are activated, the capacity to induce bone marrow mesenchymal stem cell differentiation reaches a peak level, but is not increased with greater activation rates.