Yeast glucan particles activate murine resident macrophages to secrete proinflammatory cytokines via MyD88- and Syk kinase-dependent pathways.

The therapeutic benefits of fungal beta-glucans have been demonstrated as immuno-stimulating agents. In this study, we aimed to explore the mechanisms used by yeast beta-glucan-rich particles to activate murine resident macrophages for cytokine secretion. We demonstrated that resident macrophages were effectively activated by whole yeast beta-glucan particles (WGPs), such as with the upregulation of co-stimulatory molecules and the secretion of cytokines. The binding ability of WGPs and the levels of cytokine secretion in resident macrophages were significantly inhibited by soluble yeast beta-glucan but not by blockade of zymosan glucan receptor dectin-1. In addition, WGP-stimulated cytokine secretion was partially dependent on the MyD-88 pathway but was not significantly affected in CR3-deficient (CR3(-/-)) mice. Furthermore, we showed that Syk kinase was recruited upon WGP stimulation and was required for the production of cytokines. Taken together, these observations suggest that beta-glucan recognition is necessary but not sufficient to induce inflammatory response on resident macrophages. In addition, beta-glucan particles may use differential mechanisms for cytokine secretion in resident macrophages that may modulate both innate and adaptive immunity.