GBP5-triggered AIM2 inflammasome drives host defense and exacerbates disease severity during Neospora caninum infection.

Neospora caninum is a major cause of abortion in cattle worldwide, leading to substantial economic losses in the livestock industry. As no effective drug or vaccine is currently available, a deeper understanding of the host immune response against N. caninum is essential for developing effective control strategies. The absent in melanoma 2 (AIM2) inflammasome is involved in host defense and regulation of disease pathology, while its role in N. caninum infection remains unclear. This study shows that N. caninum activates the AIM2 inflammasome in wild-type (WT) murine peritoneal macrophage (PMϕs), characterized by increased expression of AIM2, pro-IL-1β, caspase-1 p20, and IL-1β p17, along with elevated IL-1β secretion and cell death rates. Guanylate-binding proteins (GBPs) are involved in regulating AIM2 inflammasome activation. Here, we observed that both GBP2 and GBP5 were upregulated by N. caninum, but only GBP5 overexpression played a functional role, as its overexpression enhanced, whereas its knockdown significantly attenuated AIM2 inflammasome in WT PMϕs, suggesting N. caninum activates the AIM2 inflammasome in a GBP5-dependent manner. To further investigate the role of AIM2 in parasite infection, AIM2-/- mice were used. In AIM2-/- PMϕs, inflammasome activation was reduced, accompanied by increased parasite proliferation. In vivo, N. caninum-infected AIM2-/- mice exhibited higher parasite loads but showed increased survival rates, reduced macrophage recruitment, decreased levels of IFN-γ, and IL-18, and alleviated pathological damage. In summary, our findings demonstrate that the AIM2 inflammasome is activated by N. caninum in a GBP5-dependent manner and plays a dual role by restricting parasite proliferation while exacerbating disease pathology.