Semen Cuscutae has been using as a tonic for nourishing the liver and kidneys. However, the immunoregulatory effect of Semen Cuscutae is rarely studied. Dendritic cells (DCs) play a critical role in initiating immune response. Thus, DCs are regarded as a major target of immunomodulator for controlling harmful immune responses. In this study, we examined the effect of Semen Cuscutae on mouse bonemarrow-derived DC activation. We found that the n-butanol and methanol partitions of Semen Cuscutae potentially suppressed LPS-induced DC activation. HPLC chromatography showed that several flavonoids might be responsible for this inhibitory activity. Then, we identified that kaempferol was the major flavonoid to inhibit LPS-induced DC activation by reducing the production of pro-inflammatory cytokines and maturation. The inhibitory ability of kaempferol was tested at the concentration of 10 ug/ml. Importantly, consistent to the in vitro results, the recall assay in vivo showed that kaempferol significantly inhibited the T cell proliferation, indicating that kaempferol abrogated the ability of LPS-stimulated DCs to induce Ag-specific T cell activation, both in vitro and in vivo. Therefore, we demonstrate that Semen Cuscutae has immunosuppressive activity for the first time. In addition, we are the first group to report that kaempferol attenuates the DC activation and could potentially be applied in the therapy for inflammatory and autoimmune diseases.
