Structural Characterization and Immunostimulatory Activity of a New Slightly Branched β-glucan in Sporisorium reilianum-Infected Sorghum Head Smut

Sporisorium reilianum ( S. reilianum ) is an agricultural pathogen that causes disease and reduces yield in sorghum and maize crops. However, head smut-infected sorghum and maize have been traditionally utilized for edible and medicinal purposes in some regions. In this study, the structure and immunostimulatory potency of a new slightly branched β-glucan WM-0.25(P) obtained from the S. reilianum -infected sorghum head smut were explored. WM-0.25(P) was a β-glucan with a molecular weight of 69.67 kDa and was composed of β-1,6-D-Glcp as the main chain and β-1,3-D-Glcp as the side chain. There was approximately one branch for every 11 sugars on the main chain. WM-0.25(P) triggered morphological alterations, enhanced phagocytic activity, and upregulated the expression of surface molecules, while promoting the production of ROS, NO, and pro-inflammatory cytokines (IL-6, TNF-α, IL-1β) in RAW264.7 macrophages. The function blocking antibodies to toll-like receptor revealed that TLR4 mainly participated in the recognition and immunostimulatory function of WM-0.25(P). Simultaneously, WM-0.25(P) modulated macrophage inflammatory response mainly through activation of the TLR4/MyD88/NF-κB signaling pathway. The results indicated that WM-0.25(P), with a low branching degree derived from S. reilianum -infected sorghum head smut, exerted moderate immunomodulatory effects on macrophages. Further in vivo studies are warranted to evaluate its translational potential. Graphical This β-glucan (69.67 kDa) from S. reilianum -infected sorghum has a β-1,6 backbone with β-1,3 branches. It moderately activates RAW264.7 macrophages via TLR4/MyD88/NF-κB, promoting cytokine/ROS/NO production and phagocytosis.