Dectin-1-Dependent Activation of Flt3 Ligand-Induced Dendritic Cells by the Caterpillar Medicinal Mushroom Cordyceps militaris (Ascomycetes) Fruiting Body.

Cordyceps militaris, an entomopathogenic fungus traditionally used in East Asian medicine, contains 1,3-β-glucans with well-known immunomodulatory properties. Our previous research has demonstrated that both fruit body powder and hot water extract of C. militaris can activate bone marrow-derived dendritic cells through dectin-1 signaling. However, the immunological effects on Fms-like tyrosine kinase 3 ligand-induced dendritic cells (fDCs), which closely resemble steady-state conventional dendritic cells in vivo, remain unexplored. In this study, we investigated the expression of dectin-1 in fDCs and its response to C. militaris fruit body powder (RK). Flow cytometric analysis revealed that conventional and plasmacytoid dendritic cells within the fDC population expressed dectin-1, with conventional dendritic cells showing particularly robust expression. Similar expression patterns were observed in freshly isolated splenic DCs. Importantly, RK induced significant tumor necrosis factor-α production in wild-type fDCs, whereas this effect was completely abolished in dectin-1-knockout fDCs. These findings demonstrate that C. militaris fruit-body powder activates fDCs through a dectin-1-dependent pathway, providing new insights into its immunomodulatory mechanisms and potential therapeutic applications.