Toxoplasmatype II effector GRA15 has limited influencein vivo

Abstract

AbstractToxoplasma gondiiis an intracellular parasite that establishes a long-term infection in the brain of many warm-blooded hosts, including humans and rodents. Like all obligate intracellular microbes,Toxoplasmauses many effector proteins to manipulate the host cell to ensure parasite survival. While some of these effector proteins are universal to allToxoplasmastrains, some are polymorphic betweenToxoplasmastrains. One such polymorphic effector is GRA15. Thegra15allele carried by type II strains activates host NF-κB signaling, leading to the release of cytokines such as IL-12, TNF, and IL-1β from immune cells infected with type II parasites. Prior work also suggested that GRA15 promotes early host control of parasitesin vivo, but the effect of GRA15 on parasite persistence in the brain and the peripheral immune response has not been well defined. For this reason, we sought to address this gap by generating a new IIΔgra15strain and comparing outcomes at 3 weeks post infection between WT and IIΔgra15infected mice. We found that the brain parasite burden and the number of macrophages/microglia and T cells in the brain did not differ between WT and IIΔgra15infected mice. In addition, while IIΔgra15infected mice had a lower number and frequency of splenic M1-like macrophages and frequency of PD-1+ CTLA-4+ CD4+ T cells and NK cells compared to WT infected mice, the IFN-γ+ CD4 and CD8 T cell populations were equivalent. In summary, our results suggest thatin vivoGRA15 may have a subtle effect on the peripheral immune response, but this effect is not strong enough to alter brain parasite burden or parenchymal immune cell number at 3 weeks post infection.