Toxoplasma gondii KCR is a Noncanonical Modulator of CSF2 Signaling that Targets the CSF2Rα-JAK2/STAT5 Axis

Toxoplasma gondii establishes infection in hosts by deploying effector proteins that reprogram cytokine-driven immunity. While protozoan parasite-encoded macrophage migration inhibitory factor (MIF) homologs exemplify cytokine mimicry, whether T. gondii targets additional host cytokine axes remains unclear. Here, we identify a T. gondii 3-ketoacyl-CoA reductase (KCR) as a noncanonical cytokine modulator that engages the granulocyte-macrophage colony-stimulating factor (CSF2) receptor alpha chain (CSF2Rα). In HEK293T cells, forward and reverse co-immunoprecipitation (Co-IP) assays demonstrated a specific interaction between KCR and murine CSF2Rα. The recombinant KCR triggered rapid activation of canonical CSF2 signaling in RAW264.7 macrophages, inducing phosphorylation of JAK2 and STAT5 to levels comparable to murine CSF2. Functionally, KCR enhanced NADPH oxidase-dependent oxidative responses, increasing intracellular reactive oxygen species (ROS) and upregulating transcripts encoding core oxidase subunits, including CYBB, CYBA, NCF1, and NCF2. KCR also promoted phagocytic capacity, elevating FITC-dextran uptake and inducing expression of complement, Fc, and scavenger receptor genes, including CR3, CD16, CD64, MSR1, and MARCO. Notably, KCR pretreatment attenuated CSF2-induced JAK2/STAT5 phosphorylation, ROS production, and phagocytosis, consistent with competitive interference with endogenous CSF2-CSF2R signaling. Together, these findings reveal KCR as a previously unrecognized T. gondii factor that targets the CSF2/CSF2R axis to recalibrate macrophage effector functions, expanding the repertoire of parasite strategies for cytokine pathway modulation and highlighting CSF2-CSF2R signaling as a potential interface for mechanistic and therapeutic investigation in toxoplasmosis.