Recent studies report that inhibiting TNF-α might be a novel therapeutic strategy for managing brain ischemia. Our previous study reported that mesenchymal stem cell (MSC) transplantation could suppress TNF-α level in both serum and brain. However, the cell type(s) that contribute to the production of TNF-α during ischemia following MSC transplantation has not been well studied. In the present study, we found by fluorescent immunohistochemistry, that 7.95 ± 6.17% of TNF-α cells co-expressed Iba-1 in the infarct area of dMCAO rats, a majority of which were found to be CD68 (activated microglia), suggesting that resident microglial population were not the major source of TNF-α expression. 68.49 ± 5.12% of the TNF-α cells in the infarct area could be labeled by GFAP, a specific marker for astrocytes, indicating that resident GFAP astrocytes might be the major source of TNF-α expression in the infarct area. In addition to the infarct area, the GFAP/TNF-α double-positive astrocytes accounted for 73.68 ± 7.48% of the TNF-α cells in striatum and corpus callosum. The infiltrating cells, including monocytes and lymphocytes, were not the main source of TNF-α either. In response to MSC transplantation, the total TNF-α cells as well as the percentage of TNF-α-expressing astrocytes were significantly reduced in the infarct area, suggesting that MSC transplantation could suppress the expression of TNF-α by astrocytes. Taken together, the results demonstrated that resident astrocytes, but not microglia, were the major source of TNF-α expression and could be suppressed by MSC infusion.
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