Tong-fu-li-fei decoction attenuates immunosuppression to protect the intestinal-mucosal barrier in sepsis by inhibiting the PD-1/PD-L1 signaling pathway

The aim of the present study was to investigate the therapeutic effects of Tong-fu-li-fei (TFL) decoction on sepsis-induced injury to the intestinal mucosal barrier and the underlying mechanism. Cecal ligation and puncture (CLP) was used to establish a sepsis model in rats. The post-surgery death of the rats was recorded to calculate the survival rate. A 4-kD fluorescein isothiocyanate (FITC)-dextran assay was used to evaluate the intestinal permeability of the rats. The pathological state of the intestine tissues was detected by hematoxylin and eosin staining and the ultrastructural changes in the endometrium were evaluated by transmission electron microscopy. Enzyme-linked immunosorbent assay was used to determine the concentrations of interleukin (IL)-6 and tumor necrosis factor (TNF)-α in the intestinal tissues and cells. The expression levels of SHP-2 and PI3K were detected by reverse transcription-quantitative PCR and western blotting. Sorting by flow cytometry was used to obtain pure dendritic cells (DC), CD8(+) T cells and natural killer cells. Western blotting was used to evaluate the expression levels of phosphorylated (p)-AKT and AKT. The results demonstrated that the significantly decreased survival rate caused by CLP surgery was elevated by glutamine (Gln) and TFL treatment. Intestinal permeability was increased by CLP, and greatly suppressed by Gln or TFL treatment. Histopathological changes in the intestinal tissues, such as thinner barrier and atrophied mucosa, and ultrastructure changes such as sharply decreased microvilli and mitochondria dropsy, were observed on sepsis animals; these effects were ameliorated by the introduction of Gln or TFL. The upregulation of SHP-2, PI3K and p-AKT induced by CLP was reversed by TFL. The release of IL-6 and TNF-α was elevated and the expression of SHP-2, PI3K and p-AKT was suppressed in the co-cultural system of DC cells and CD8(+) T cells by TFL. Overall, TFL decoction may attenuate immunosuppression to protect intestinal mucosal barrier in sepsis via inhibiting the programmed death1/programmed cell death ligand 1 signal pathway.