Anti-allergic Effect of Soluble Beta-glucan on Japanese Cedar Pollinosis and Mechanism Underlying Its Allergy-ameliorating Action

Japanese cedar (sugi) pollinosis is triggered by sensitization to sugi pollen, which contains sugi antigens, sugi basic proteins (SBP: Cryj1 and Cryj2), and adjuvant polysaccharides, insoluble {beta}-glucan particles (IBG: a dectin-1 agonist). The presence of IBG in sugi pollen enhances the production of SBP-specific IgE, which participates in inflammatory response via activation of mast cells to lead to their degranulation, resulting in sneezing. Another {beta}-glucan derived from black yeast, soluble {beta}-glucan (SBG: a dectin-1 antagonist), is known to have an anti-allergic function. Herein, we demonstrated that oral administration of SBG suppressed both SBP-specific IgE production and SBP-induced sneeze in sugi pollinosis mice model. DNA microarray analyses revealed previously unknown mechanisms underlying SBG-mediated anti-allergy action. SBG ameliorated the dysregulated expression of 16 immune-inflammatory genes that were unusually either up- or down-regulated in sugi pollinosis mice. Based on the DNA microarray informatics, it was suggested that SBG mitigated the IBG-mediated hyper-response of IgE production and inflammatory reaction in immune-inflammatory cells, B and T cells, antigen-presenting cells, and granulocytes (neutrophils and eosinophils) within iliac lymph nodes. The SBG-mediated inhibition of SBP-induced sneezing in pollinosis mice results from a decline in SBP-specific IgE level. The oral administration of SBG influenced gut microbiota, notably enhancing beneficial bacteria such as bifidobacteria. Consequently, it is plausible that short-chain fatty acids, produced by these beneficial bacteria, inhibited mast cell degranulation, leading to a reduction in sneezing. Collectively, SBG demonstrated anti-allergic effects against sugi pollinosis by inhibiting the immune response, specifically SBP-induced IgE production, as well as reducing the inflammatory reaction characterized by SBP-induced sneezing.