Research on immune activation and mechanism of Angelica sinensis polysaccharide as potential adjuvant in cells

The purpose of this study is not only to investigate the effects of Angelica sinensis polysaccharide (ASP) as a potential vaccine adjuvant on immune activation and cytokine release in RAW264.7 macrophages, but also to elucidate its underlying involved signaling mechanisms. Cell viability was evaluated by the CCK-8 assay. Flow cytometry was used to analyze the influence of ASP at five distinct concentration gradients on the expression of cluster of differentiation (CD) 80, CD86, and major histocompatibility complex Ⅱ (MHC Ⅱ) on RAW264.7 cell surfaces. The levels of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in cell culture supernatant were determined by enzyme-linked immunosorbent assay (ELISA) method. Molecular techniques, including quantitative polymerase chain reaction (qPCR) were utilized to assess the mRNA expression levels of Toll-like receptor 4 (TLR4)-myeloid differentiation factor 88 (MyD88)-TNF receptor associated factor 6 (TRAF6)-nuclear factor kappa-B (NF-κB) signaling pathway. The levels of TRAF6, and the phosphorylation levels of IκB kinase (IKK) and p65 proteins were detected by Western blot. The results show that ASP at varying concentrations promote the proliferation of RAW264.7 cells without cytotoxicity. Surface molecules CD80, CD86, and MHC Ⅱ on RAW264.7 cells showed statistically significant up-regulation in response to ASP compared to the blank control (P < 0.05), with a dose-dependent effect within an optimal range. Furthermore, ASP also elevated cytokines IL-6 and TNF-α secretion levels by RAW264.7 cells compared to the normal control (P < 0.05), exhibiting a dose-response relationship within a specific concentration span. The qPCR results indicated that ASP groups at different concentrations all led to upregulation of mRNA expression levels of TLR4, MyD88, TRAF6, and NF-κB signaling pathway. The expression levels of TRAF6, p-IKK and p-p65 were increased by different concentrations of ASP. The TLR4 inhibitor TAK-242 significantly reduced the secretion of cytokines induced by APS (P < 0.05). This study highlights the immunostimulatory properties of ASP, emphasizing its potential as a vaccine adjuvant. By significantly enhancing the expression of co-stimulatory molecules and cytokines via the TLR4-MyD88-TRAF6-NF-κB signaling pathway, ASP offers a promising approach for modulating immune responses.