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Macrophages can initiate innate immune responses against microbes and cancer. The aim of this study was to elucidate the effects of Brassica rapa L. on macrophages. The production of interleukin (IL)-6, tumor necrosis factor (TNF)-α, and interferon-γ induced by the insoluble fraction of B. rapa L. was decreased in macrophage-depleted spleen cells compared with controls. The insoluble fraction of B. rapa L. induced expression of H-2Kb, I-Ab, CD40, and CD86, production of cytokines and nitric oxide, and phagocytic activity in RAW264 cells. After treatment with the insoluble fraction, IL-6 and TNF-α production was significantly decreased by anti-Toll-like receptor (TLR)2 mAb or polymyxin B compared with the control. Furthermore, insoluble fraction-mediated cytokine production was significantly lower in peritoneal macrophages from TLR2−/− and TLR4−/− mice compared with wild-type mice. These results suggest that B. rapa L. is a potentially effective immunomodulator for activating macrophages to prevent infections. [ABSTRACT FROM AUTHOR]