# Toxoplasma gondii Type I TR and ROP16 Synergistically Downregulate IL-12 to Inhibit Host Reactive Oxygen Species Production

## TL;DR

This study shows that two Toxoplasma gondii proteins, TR and ROP16, work together to reduce inflammation and protect the parasite from immune damage.

## Contribution

The study reveals a synergistic mechanism between TR and ROP16 in T. gondii to inhibit host ROS production and immune response.

## Key findings

- Deleting both TR and ROP16 genes reduced T. gondii's growth and virulence.
- The double deletion increased ROS levels and lipid oxidation in the parasite and host cells.
- TR and ROP16 synergistically suppressed IL-12, reducing host ROS production.

## Abstract

Toxoplasma gondii is an obligate intracellular opportunistic protozoan parasite. T. gondii invasion disturbs the balance between reactive oxygen species (ROS) production and antioxidant capacity in the host, triggering the oxidative stress response. Thioredoxin reductase (TR) of T. gondii helps to escape ROS-induced damage in the host, whereas T. gondii rhoptry protein 16 (ROP16) downregulates host innate immunity to suppress excessive inflammation and inhibit ROS production. However, whether TR and ROP16 synergistically promote resistance to ROS-induced damage remains unclear. Here, we used the CRISPR/Cas9 technology to successfully obtain a double TR and ROP16 gene knockout T. gondii strain. The double deletion of TR and ROP16 in T. gondii weakened its growth ability in vitro and decreased its virulence in vivo. Moreover, the double deletion of TR and ROP16 resulted in a lower antioxidant capacity, higher degree of lipid oxidation, and elevated ROS levels in the parasite and host cells. Interestingly, the deletion of the TR and ROP16 genes in T. gondii synergistically increased IL-12 levels, which triggered host cells to produce more ROS to resist T. gondii infection. These results show that TR and ROP16 in T. gondii play a synergistic role, facilitating resistance to ROS damage incurred by host immune cells through different pathways.