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Objective.To investigate the effect of anti-tumor necrosis factor(TNF)-α on the intestinal mucosal permeability in dextran sulfate sodium (DSS)-induced colitis and to determine its associated mechanism.Methods.Experimental colitis was induced in C57BL/6J mice by administration of 5% DSS.Anti-TNF-α was injected intraperitoneally at doses of 5 mg/kg twice a week (d1 and d4).The disease activity index (DAI) scores were evaluated,and colon tissue was collected for the assessment of histological changes.The myeloperoxidase (MPO) activity,TNF-α and interferon-γ (IFN-γ) levels in the colon were determined.The small intestinal mucosa was ultrastructurally examined with transmission electron microscopy,epithelial myosin light chain kinase (MLCK) protein expression and enzymatic activity were determined,and intestinal permeability was assayed using FITC-dextran(FD-4) and Evans blue(EB).Results.Anti-TNF-α was found effective in reducing the DAI score and histological index (HI) score,and decreasing MPO activity,TNF-α and IFN-γ levels.The amount of FD-4 in blood and EB permeating into the intestine were decreased by anti-TNF-α in colitis mice.The small intestinal epithelial MLCK protein expression and enzymatic activity were downregulated by anti-TNF-α.Conclusions.Anti-TNF-α showed a significant anti-colitis effect in colitis mice.The mechanism is partly associated with inhibiting the epithelial MLCK protein expression and enzymatic activity,which resulting in ameliorated intestinal mucosal permeability.