TLR9 and infection: In the present study, we further found that, with G. duodenalis trophozoite stimulation, the secretion levels of IL-6 and TNF-α were significantly lower in siTLR9-treated mouse macrophages than in WT mouse macrophages, suggesting that activated TLR9 not only has a role in the regulation of cytokine secretion by the host in the early stages of infection but also plays a host-protective role.