Structural characterization and immune activity evaluation of polysaccharide purified from Viola phillipica

This study investigated the structure of Viola phillipica polysaccharide (VPP) and its effect as an immune adjuvant for the Newcastle disease vaccine (ND Vaccine). The results showed that VPP comprised of the galacturonic acid, galactose, rhamnose, arabinose with the molar ratio of 36.20: 23.41: 19.72: 11.54 and a molecular weight (Mw) of 1080 kDa. Additionally, the composition of VPP was assessed via FT-IR, methylation, AFM and SEM analyses, indicating that the backbone of the VPP was consisted of T-Ara (f), T-Gal (p), 4-Gal (p)-UA, and T-Rha (p) linkages. Furthermore, VPP was used as an immune adjuvant in combination with ND vaccine in chickens. Remarkable enhancements were observed in the thymus, spleen, and bursa indices of the chickens, the serum levels of ND antibodies and the expression of IL-4 and IFN-γ cytokines, thereby fostering the proliferation of T and B lymphocytes within the spleen. Notably, histopathological analysis indicated that the VPP groups showed increased lymphoid follicles and splenic nodules, as well as greater splenic red pulp density and bursa of Fabricius area. In summary, these findings suggest that VPP could serve as an adjuvant to enhance the immunogenicity of NDV.