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

## TL;DR

This study shows how Giardia duodenalis uses its MIF protein to trigger inflammation and intestinal damage in the host through a specific immune pathway.

## Contribution

The study reveals a novel mechanism by which G. duodenalis MIF activates the host's NLRP3 inflammasome via CD74, leading to intestinal damage.

## Key findings

- GdMIF activates the CD74-NF-κB-NLRP3 pathway in macrophages, causing pyroptosis and pro-inflammatory cytokine release.
- Blocking GdMIF or NLRP3 in gerbils reduced intestinal inflammation and tissue damage caused by G. duodenalis infection.
- GdMIF has dopamine tautomerase activity and is secreted by the parasite.

## Abstract

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.

Giardia duodenalis is a globally important protozoan parasite that infects the small intestine and causes diarrheal disease. The mammalian macrophage migration inhibitory factor (MIF) is a critical host cytokine governing immune regulation and inflammatory responses. GdMIF is a homolog of mammalian MIF, however, its roles in G. duodenalis infection remain unknown. In this study, we demonstrated that GdMIF is secreted by G. duodenalis and possesses dopachrome tautomerase activity. GdMIF specifically binds to the host receptor CD74 on macrophages, triggering the NF-κB signaling cascade and subsequent activation of the NLRP3 inflammasome. This cascade caused pyroptosis and robust secretion of pro-inflammatory cytokines (IL-1β, IL-6, IL-12, IL-18, and TNF-α). In a gerbil model of giardiasis, blocking GdMIF with specific antibodies or pharmacologically inhibiting NLRP3 significantly reduced intestinal inflammation, preserved goblet cells and tight-junction integrity, and alleviated villous damage. These findings reveal a novel mechanism by which G. duodenalis utilizes its own MIF homologue to exacerbate host intestinal injury via the CD74-NF-κB-NLRP3 axis. Targeting GdMIF or NLRP3 may offer new therapeutic avenues for preventing or treating giardiasis and its associated morbidities.