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.