Investigating the Effects of Gardenia Polysaccharides on LPS-Induced Immune Injury in Mice and Exploring the Molecular Mechanisms Underlying Its Regulatory Effect on the Immune Function of Macrophages

This study investigated the protective effects of <i>Gardenia jasminoides</i> Ellis polysaccharides (GP) on lipopolysaccharide (LPS)-induced immunosuppression and oxidative stress in mice and explored how GP modulates macrophage polarization through the TLR4/NF-κB signaling axis. The results showed that GP notably restored thymus and spleen indices in LPS-treated mice, markedly decreased the serum concentrations of malondialdehyde, and enhanced superoxide dismutase activity and total antioxidant capacity. In RAW 264.7 macrophage cultures, GP displayed immunostimulatory effects by improving phagocytic activity, promoting NO synthesis, and enhancing the secretion of pro-inflammatory cytokines, including IL-1β, IL-6, and TNF-α. These effects were observed in cells not pretreated with TAK-242 or PDTC; however, they were not observed in cells pretreated with these inhibitors. At 300 µg/mL concentration, GP markedly enhanced the transcriptional levels of iNOS and cytokine genes. Protein analysis revealed significant upregulation of TLR4, MyD88, TRAF6, NF-κB RelA/p65, and phosphorylated p65. Fluorescence imaging confirmed the nuclear translocation of p65. Collectively, these findings indicated that GP reversed systemic immunosuppression and oxidative stress, offering foundational insights for developing natural immune regulators. The observed immunomodulatory properties of GP are likely mediated through the TLR4/NF-κB signaling pathway.