The cytokine stimulating activity of (1→3)-β-d-glucans is dependent on the triple helix conformation Original Research Article

The immunomodulating properties of comb-like branched (1→3)-β-d-glucans scleroglucan, schizophyllan and lentinan depend on branching pattern, molecular weight and higher-order structure. The effect of weight average molecular weight Mw and higher order structure of scleroglucan, on stimulation of human monocytes cultured in vitro to secrete tumor necrosis factor-α (TNF-α) was investigated. The higher order structures of the scleroglucan samples were determined by electron microscopy. The data showed that the samples with a linear wormlike, triple helical structure with Mw less than 50×104 g/mol or larger than 110×104 g/mol stimulated the monocytes more efficiently than samples with Mw in the range (67–110)×104 g/mol. The denaturation of the linear triple helices by NaOH (>0.25 M), followed by neutralization yielded blends of linear and macrocyclic topologies with concomitant irreversible reduction of the cytokine inducing activity compared with the untreated scleroglucans. The dose-dependent ability to activate monocytes to cytokine production was not restored following annealing of the denatured–renatured samples, despite the fact that electron micrographs revealed similar structures of these annealed samples to the starting material. Pre-incubation of monocytes with antibodies against cluster of differentiation antigens CD14 or CD11b reduced the scleroglucan potency to stimulate TNF-α secretion mainly for mAb against CD14 in the presence of serum.