The cytokine stimulating activity of (1 -> 3)-beta-D-glucans is dependent on the triple helix conformation

The immunomodulating properties of comb-like branched (1 --> 3)-beta -D-glu cans scleroglucan, schizophyllan and lentinan depend on branching pattern, molecular weight and higher-order structure. The effect of weight average m olecular weight M-w and higher order structure of scleroglucan, on stimulat ion of human monocytes cultured in vitro to secrete tumor necrosis factor-a lpha (TNF-alpha) was investigated. The higher order structures of the scler oglucan samples were determined by electron microscopy. The data showed tha t the samples with a linear wormlike, triple helical structure with M-w les s than 50 x 10(4) g/mol or larger than 110 x 10(4) g/mol stimulated the mon ocytes more efficiently than samples with M-w in the range (67-110) x 104 g /mol. The denaturation of the linear triple helices by NaOH (> 0.25 M), fol lowed 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 ac tivate monocytes to cytokine production was not restored following annealin g of the denatured-renatured samples, despite the fact that electron microg raphs revealed similar structures of these annealed samples to the starting material. Pre-incubation of monocytes with antibodies against cluster of d ifferentiation antigens CD14 or CD11b reduced the scleroglucan potency to s timulate TNF-alpha secretion mainly for mAb against CD14 in the presence of serum. (C) 2000 Elsevier Science Ltd. All rights reserved.