AUTHOR=Kongsomboonvech Angel K. , García-López Laura , Njume Ferdinand , Rodriguez Felipe , Souza Scott P. , Rosenberg Alex , Jensen Kirk D. C. 

TITLE=Variation in CD8 T cell IFNγ differentiation to strains of Toxoplasma gondii is characterized by small effect QTLs with contribution from ROP16

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=13

YEAR=2023

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2023.1130965

DOI=10.3389/fcimb.2023.1130965

ISSN=2235-2988

ABSTRACT=<sec><title>Introduction</title><p><italic>Toxoplasma gondii</italic> induces a strong CD8 T cell response characterized by the secretion of IFNγ that promotes host survival during infection. The initiation of CD8 T cell IFNγ responses <italic>in vitro</italic> differs widely between clonal lineage strains of <italic>T. gondii</italic>, in which type I strains are low inducers, while types II and III strains are high inducers. We hypothesized this phenotype is due to a polymorphic “<underline>R</underline>egulator <underline>O</underline>f <underline>C</underline>D8 <underline>T</underline> cell <underline>R</underline>esponse” (ROCTR).</p></sec><sec><title>Methods</title><p>Therefore, we screened F1 progeny from genetic crosses between the clonal lineage strains to identify ROCTR. Naïve antigen-specific CD8 T cells (T57) isolated from transnuclear mice, which are specific for the endogenous and vacuolar TGD057 antigen, were measured for their ability to become activated, transcribe <italic>Ifng</italic> and produce IFNγ in response to <italic>T. gondii</italic> infected macrophages.</p></sec><sec><title>Results</title><p>Genetic mapping returned four non-interacting quantitative trait loci (QTL) with small effect on <italic>T. gondii</italic> chromosomes (chr) VIIb-VIII, X and XII. These loci encompass multiple gene candidates highlighted by ROP16 (chrVIIb-VIII), GRA35 (chrX), TgNSM (chrX), and a pair of uncharacterized NTPases (chrXII), whose locus we report to be significantly truncated in the type I RH background. Although none of the chromosome X and XII candidates bore evidence for regulating CD8 T cell IFNγ responses, type I variants of ROP16 lowered <italic>Ifng</italic> transcription early after T cell activation. During our search for ROCTR, we also noted the parasitophorous vacuole membrane (PVM) targeting factor for dense granules (GRAs), GRA43, repressed the response suggesting PVM-associated GRAs are important for CD8 T cell activation. Furthermore, RIPK3 expression in macrophages was an absolute requirement for CD8 T cell IFNγ differentiation implicating the necroptosis pathway in T cell immunity to <italic>T. gondii</italic>.</p></sec><sec><title>Discussion</title><p>Collectively, our data suggest that while CD8 T cell IFNγ production to <italic>T. gondii</italic> strains vary dramatically, it is not controlled by a single polymorphism with strong effect. However, early in the differentiation process, polymorphisms in ROP16 can regulate commitment of responding CD8 T cells to IFNγ production which may have bearing on immunity to <italic>T. gondii</italic>.</p></sec>