β-Glucans are glucose polymers produced by a variety of plants and microorganisms and have been investigated extensively in tumor immunotherapy.Our previous studies have demonstrated that soluble, small molecular weight, yeast-derived β-glucan is capable of binding to the lectin site of complement receptor 3 (CR3, CD1 1b/CD18) and priming leukocyte CR3 to elicit cytotoxicity of iC3b-opsonized tumor cells.In this study, we investigated the cellular and molecular mechanism of action for particulate yeast-derived β-glucan in tumor immunotherapy.In vitro studies demonstrated that particulate-glucan, but not soluble β-glucan, stimulated DCs for up-regulation of surface accessory molecules and production of proinflammatory cytokines such as IL-12 and TNF-α.In vivo treatment with orally administered particulate β-glucan led to the activation and maturation of DCs that captured apoptotic tumor cells.