ABSTRACT
Objective To study the mechanism of adaptive immunity against Rhizopus arrihizus (R. arrihizus) infections. Methods Bone marrow derived dendritic cells (BMDCs) were separated from C57BL/6 mice and Card9-/- mice and then were cultured in vitro. Resting spores and swollen spores of R. arrihizus were in vitro co-cultured with BMDCs with or without Syk inhibition. Secretion of cytokines ( IL-23, IL-1βand IL-12) was analyzed by ELISA after 24 hours of culture. Na?ve T cells derived from C57BL/6 mice were in vitro co-cultured with spore-stimulated BMDCs for four days. Levels of IL-17A and IFN-γ in supernatants of cell culture were analyzed by ELISA. Flow cytometry was performed to analyze T cell differ-entiation. Confocal microscopy was used to observe the images of stained β-glucan on the surface of resting and swollen spores. Swollen spores were co-cultured with Dectin-1, Dectin-2, TLR2 and mannose receptor ( MMR) , and the binding results were analyzed by flow cytometry. Results Swollen spores but resting spores could induce the maturation of BMDCs and promote the secretion of cytokines (IL-23, IL-1βand IL-12). Co-culturing T cells with swollen spore-stimulated BMDCs enhanced their differentiation to Th17 and Th1. In addition, swollen spores promoted the secretion of Th1-related cytokine ( IFN-γ) and Th17-related cytokine (IL-17A). Adding Syk inhibitor to Card9-/-BMDCs or wild type BMDCs significantly inhibited the secretion of cytokines and T cell differentiation, especially in the Card9-/- group. β-glucan was overserved on the surface of swollen spores, but not on resting spores. On the surface of swollen spores existed pathogen associated molecular patterns ( PAMPs) that could bind with Dectin-1 and TLR2. Conclusion Swollen spores of R. arrihizus could active BMDCs to secrete cytokines of IL-23, IL-1β and IL-12 and trigger T cell responses in vitro. The possible mechanism might be associated with β-glucan exposed on the surface of swollen spores that binds with Dectin-1. The responses between BMDCs and R. arrihizus are Syk-Card9-dependent.