β-Glucans inhibit intracellular growth of Mycobacterium bovis BCG but not virulent Mycobacterium tuberculosis in human macrophages

The yeast polysaccharide, beta-glucan, has been shown to promote both anti-microbial and anti-tumor activities through its interaction with macrophages. Here we analyzed the effects of an insoluble whole glucan particle (WGP), a 1,3/1,6-beta-glucan from Saccharomyces cerevisiae, and a soluble poly-1-6-beta-D-glucopyranosyl-1-3-beta-D-glucopyranose (PGG), a hydrolytic product of WGP, on the anti-microbial response of human macrophages against mycobacterial infection. Treatment of macrophages with WGP and PGG significantly decreased cell association and intracellular growth of Mycobacterium bovis BCG, but not Mycobacterium tuberculosis (M.tb) when compared to untreated controls. We characterized the influence of beta-glucans on the generation of macrophage oxidative products and pro-inflammatory cytokines, two important anti-microbial defense mechanisms. WGP but not PGG treatment enhanced the oxidative response of macrophages as determined by the 2',7'-dichlorofluorescin (DCF) assay. WGP treatment also induced macrophages to produce pro-inflammatory cytokines. The beta-glucan receptor, Dectin-1, was found to be involved in the WGP-induced macrophage oxidative burst and intracellular growth inhibition of M. bovis BCG. This report indicates that although some forms of beta-glucan are able to stimulate the respiratory burst and cytokine production in human macrophages, and exhibit antimicrobial properties against M. bovis BCG, the beta-glucans tested here did not inhibit growth of M.tb within human macrophages. (C) 2011 Elsevier Ltd. All rights reserved.