Immune-enhancing activity of a plant-derived acid polysaccharide LCAP on influenza and respiratory syncytial virus vaccines.

Polysaccharides, given their immunomodulating properties, biocompatibility, and biodegradability, have been extensively studied for their potential as vaccine adjuvants. The structural characterization of polysaccharides and their application as vaccine adjuvants have garnered significant attention. In this study, an acidic polysaccharide, LCAP, was isolated from a natural plant, and its immune-enhancing activity as a vaccine adjuvant was investigated. LCAP was obtained through aqueous extraction, protein removal, and column chromatography purification, with a purity of approximately 94%. The molecular weight of LCAP was determined to be 27.4 kDa, primarily composed of acidic monosaccharides. X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy mapping (EDS-mapping) experiments demonstrated the protein adsorption capacity of LCAP in vitro. Furthermore, the immunostimulatory effect of LCAP was investigated by mixing it with the antigens to immunize mice models. LCAP significantly enhanced both humoral and cellular immune responses to an influenza A virus (IAV) H3N2 vaccine. Mice receiving LCAP-adjuvanted vaccine (H3N2-LCAP) demonstrated higher titers of specific IgG and the overall neutralizing antibodies. The activation of Th1 and Th2 immune responses was also enhanced in these mice, with an inclined enhancement of Th1 response. This was accompanied by an increased frequency of germinal center (GC) B cells and T follicular helper (Tfh) cells, which collectively promoted robust humoral immunity. Additionally, similar immunostimulatory effects were also observed when LCAP was formulated with a respiratory syncytial virus (RSV) vaccine. In terms of biosafety, LCAP exhibited no significant toxicity to major organs in mice. In summary, LCAP holds promising potential as a novel vaccine adjuvant, offering new insights for vaccine development.