Macrophage migration inhibitory factor of zoonotic Giardia duodenalis triggers TLR4-MAPK/AKT/NLRP3 pathways to regulate inflammatory response.

Giardia duodenalis is an important zoonotic protozoan that has a significant negative impact on public health worldwide. G. duodenalis macrophage migration inhibitory factor (GdMIF) has close similarity with mammalian MIF, yet its immunomodulatory role remains unclear. This study demonstrated that G. duodenalis secretes GdMIF, which functions as a potent immunostimulator in mouse peritoneal macrophages. Recombinant GdMIF (rGdMIF) upregulated TLR2/4 expression, induced robust cytokines secretion, and activated the MAPK, AKT, and NF-κB signaling pathways. Mechanistically, rGdMIF activated MAPK and AKT pathways via TLR4, but not TLR2. TLR4 deficiency (TLR4 -/-) impaired cytokines production and reduced phosphorylation of p38, ERK, and AKT. Inhibition of p38 or ERK further suppressed cytokines release, while AKT inhibition slightly enhanced cytokines production, whereas TLR2 -/- had no effect. Moreover, rGdMIF activated the NLRP3 inflammasome in a TLR4- and NLRP3-dependent manner. These findings demonstrated that GdMIF is a novel G. duodenalis-derived pathogen-associated molecular pattern (PAMP) recognized by TLR4, providing new insights into host-parasite immune interactions.