The effect of beta-glucans on porcine leukocytes.

beta-Glucans are conserved glucose polymers found in the cell walls of plants, fungi, yeasts and bacteria. They have the capacity to activate innate immunity, thereby enhancing defence barriers. Besides differences in type of linkage and branching, beta-glucans can vary in solubility, molecular mass, tertiary structure, polymer charge and solution conformation. All these characteristics may influence their immunomodulating effects. In this study, the effect of seven beta-glucans that differed in origin (fungi, yeast, seaweed, bacteria or algae) and structure (linear or branched; soluble, gel or particulate) were tested on peripheral blood mononuclear cells (PBMC) and neutrophils of the pig. We looked at lymphocyte proliferation, reactive oxygen species (ROS), production by neutrophils and monocytes and cytokine production. The soluble beta-glucans Laminarin and Sleroglucan did not activate ROS-production of monocytes and neutrophils while the particulate beta-glucans (beta-glucan from algae (Euglena gracilis)) and glucan preparations from baker's yeast (Macrogard, Saccharomyces cerevisiae and Zymosan) had a stimulating effect. The highest stimulation of lymphocyte proliferation occurred by Curdlan (bacteria), Zymosan and the beta-glucan of E. gracilis, especially at high concentrations (200 microg/ml and 800 microg/ml). TNF-alpha was particularly stimulated by Macrogard and S. cerevisiae, while all beta-glucans (except Laminarin) induced IL-1beta. Furthermore, it was interesting that all beta-glucans and in particular Curdlan, gave rise to IL-10 secretion, whereas any beta-glucan induced the release of IL-8, IL-4, IL-12, IL-6 or IFN-gamma.