RIPK3 facilitates host and pathogen interactions after oral Toxoplasma gondii infection

Abstract

Toxoplasma gondii infection activates pattern recognition receptor (PRR) pathways that drive innate inflammatory responses to control infection. Necroptosis is a pro-inflammatory cell death pathway apart of the innate immune response that has evolved to control pathogenic infection. In this study we further defined the role of Z-DNA binding protein 1 (ZBP1) as a PRR and assessed its contribution to necroptosis as a host protection mechanism to T. gondii infection. We found that ZBP1 does not induce pro-inflammatory necroptosis cell death and ZBP1 null mice have reduced survival after oral T. gondii infection. In contrast, mice deleted in receptor-interacting serine/threonine-protein kinase 3 (RIPK3-/-), a central mediator of necroptosis, have significantly improved survival after oral T. gondii infection even with higher parasite burden. The physiological consequences of RIPK3 activity did not show any differences in intestine villi immunopathology but RIPK3-/- mice showed higher immune cell infiltration and edema in the lamina propria. The contribution of necroptosis to host survival was clarified with mixed lineage kinase domain like pseudokinase null (MLKL-/-) mice. We found MLKL-/- mice to succumb to oral T. gondii infection the same as wild type mice, indicating necroptosis-independent RIPK3 activity impacts host survival. These results provide new insights on the impacts of pro-inflammatory cell death pathways as a mechanism of host defense to oral T. gondii infection.