Co-stimulation of TLR4 and Dectin-1 Induces the Production of Inflammatory Cytokines but not TGF-beta for Th17 Cell Differentiation

ABSTRACT

Collaboration of TLR and non-TLR pathways in innate immune cells, which acts in concert for the induction of inflammatory cytokines, can mount a specific adaptive immune response tailored to a pathogen. Here, we show that murine DC produced increased IL-23 and IL-6 when they were treated with LPS together with curdlan that activates TLR4 and dectin-1, respectively. We also found that the induction of the inflammatory cytokine production by LPS and curdlan requires activation of IKK. However, the same treatment did not induce DC to produce a sufficient amount of TGF-beta. As a result, the conditioned media from DC treated with LPS and curdlan was not able to direct CD4+ T cells to Th17 cells. Addition of TGF-beta but not IL-6 or IL-1beta was able to promote IL-17 production from CD4+ T cells. Our results showed that although signaling mediated by LPS together with curdlan is a potent stimulator of DC to secrete many pro-inflammatory cytokines, TGF-beta production is a limiting factor for promoting Th17 immunity.