Human cells fight Toxoplasma differently from mouse cells, and much of how they do it is still unknown. In a new preprint, led by postdoc Caroline de Moraes de Siqueira with graduate student Stephanie Martinez-Beltran, we show that human cells recruit the lipid-remodeling enzyme RARRES3 to the parasite’s vacuole after interferon-γ stimulation, and that RARRES3 forces the parasite to leave the cell prematurely, killing the host cell in the process.
The parasite counters with an enzyme of its own. GRA66, a vacuole-membrane protein predicted to be an NAPE-hydrolyzing phospholipase D, is required to prevent that premature egress. Parasites lacking GRA66 egress early, kill their host cell and replicate poorly, and a catalytic-site mutant of the zinc-binding motif rescues none of it, so the enzymatic activity is needed. Deleting RARRES3 restores normal egress in Δgra66 parasites but not the replication defect, pointing to a second consequence of losing GRA66.
Strikingly, this works independently of RNF213, the E3 ubiquitin ligase thought to dominate interferon-γ-dependent restriction of Toxoplasma in human cells. That makes lipid remodeling of the vacuole membrane a distinct arm of human cell-autonomous immunity, and GRA66 a candidate drug target. The work was done with Jörn Coers at Duke.
Read the preprint: Toxoplasma gondii GRA66 prevents premature egress driven by the host phospholipase RARRES3, independently of RNF213. bioRxiv 2026.