Giardia duodenalis MIF induces host intestinal damage via CD74 receptor mediated NLRP3 inflammasome activation.

Giardia duodenalis is an important zoonotic protozoan that mainly causes diarrhea, has a significant negative impact on public health worldwide. Macrophage migration inhibitory factor (MIF) as an inflammatory mediator in both innate and adaptive immune responses, and parasite-derived MIF is involved in inducing the host's immune response or causing disease. However, the role of G. duodenalis MIF (GdMIF) in giardiasis remains to be elucidated. In the present study, CD74-NF-κB-NLRP3 inflammasome activation induced by rGdMIF was systematically investigated in vitro and in vivo, and its effect on intestinal damage was examined in G. duodenalis-infected gerbils. We found that GdMIF was an exocrine protein with dopamine tautomerase activity. GdMIF could activate NF-κB and the NLRP3 inflammasome, increase GSDMD-processing and promote Lactate Dehydrogenase (LDH) and pro-inflammatory cytokine release. The interaction of CD74 molecule with rGdMIF was validated by Co-IP and BiFC. Furthermore, knockdown of CD74 and NF-κB significantly inhibited NLRP3 inflammasome activation and pro-inflammatory cytokine production in macrophages stimulated by rGdMIF. Gerbils were infected with G. duodenalis in the presence of a GdMIF blocking antibody showed lower NLRP3 expression, and milder intestinal damage compared with that of the normal G. duodenalis infection group. Inhibition of NLRP3 alleviated intestinal damage caused by G. duodenalis infection. In summary, these findings suggest that GdMIF induces NLRP3 inflammasome activation and pyroptosis by interacting with CD74 receptor, subsequently eliciting a pro-inflammatory response which lead to intestinal damage.