Macrophages play an essential role in the early immune response against Toxoplasma and are the cell type preferentially infected by the parasite in vivo. Interferon gamma (IFNγ) elicits a variety of anti-Toxoplasma activities in macrophages. Using a genome-wide CRISPR screen we identify 353 Toxoplasma genes that determine parasite fitness in naїve or IFNγ-activated murine macrophages, seven of which are further confirmed. We show that one of these genes encodes dense granule protein GRA45, which has a chaperone-like domain, is critical for correct localization of GRAs into the PVM and secretion of GRA effectors into the host cytoplasm. Parasites lacking GRA45 are more susceptible to IFNγ-mediated growth inhibition and have reduced virulence in mice. Together, we identify and characterize an important chaperone-like GRA in Toxoplasma and provide a resource for the community to further explore the function of Toxoplasma genes that determine fitness in IFNγ-activated macrophages.

巨噬细胞在针对弓形虫的早期免疫反应中起着至关重要的作用，是体内优先被寄生虫感染的细胞类型。γ 干扰素 (IFNγ) 在巨噬细胞中引发多种抗弓形虫活性。使用全基因组 CRISPR 筛选，我们鉴定出 353 种弓形虫确定幼稚或 IFNγ 激活的小鼠巨噬细胞中寄生虫适应性的基因，其中 7 个已得到进一步证实。我们表明这些基因中的一个编码致密颗粒蛋白 GRA45，它具有伴侣样结构域，对于 GRA 正确定位到 PVM 和 GRA 效应子分泌到宿主细胞质中至关重要。缺乏 GRA45 的寄生虫更容易受到 IFNγ 介导的生长抑制的影响，并且对小鼠的毒力降低。我们一起确定并描述了弓形虫中重要的伴侣样 GRA，并为社区提供了资源，以进一步探索决定 IFNγ 激活的巨噬细胞适应性的弓形虫基因的功能。