Scleroglucan is a β-glucan with a β-1,3-linked main chain and β-1,6-linked side chains. It shares the same chemical structure as schizophyllan, which is well known for its antitumor activity, and scleroglucan is also recognized as a ligand for Dectin-1. The antitumor and immunomodulatory activities of β-glucans mediated by Dectin-1 have been reported to be significantly influenced by factors such as molecular weight, degree of branching, and stereochemical structure. Notably, it has been reported that particulate β-glucans, rather than soluble β-glucans, must be presented as ligands to activate Dectin-1 signaling.

In our laboratory, we confirmed that scleroglucan aqueous solution forms a true gel when left at 4°C for over 20 hours. In this context, a true gel refers to a semi-solid state containing a large amount of water and exhibiting a distinct fracture surface upon rupture. Achieving this gel state requires partial association between polymers to form a three-dimensional network structure throughout the material. Compared to the gel, the aqueous solution of soluble β-glucan is a liquid state where individual molecules are dispersed in water, while aqueous dispersions of insoluble particulate β-glucan can be regarded as suspensions where particles formed by the aggregation of numerous molecules are dispersed in water. Therefore, the true gel state of scleroglucan is considered to be distinct from both solution state of scleroglucan and the dispersion state of insoluble particulate scleroglucan. This study investigated the effect of the gel state—neither a solution nor an insoluble β-glucan suspension—on the biological activity of scleroglucan.

A 0.6 wt% scleroglucan aqueous solution containing 70% glycerol formed a true gel upon cooling and maintained its gel state even at 40°C. We examined both applying this true gel directly to the culture plate and applying it to the culture plate in a microgel state. Microscopic observation of the microgel revealed rod-shaped gels exhibiting anisotropy. To evaluate the degree of Dectin-1 activation, the amount of TNFα released from macrophage-like cultured cells RAW264 was compared between cases where this microgel was added and cases where scleroglucan and glycerol in solution were added as a control. The amount of TNFα released from cultured cells to which scleroglucan solution was added to the medium was significantly increased compared to when it was not added. At the conference, we will present the effect of true scleroglucan gel on TNFα release compared to scleroglucan solution or suspension.