Toxoplasma gondii PPM3H regulates the parasite virulence and modulates host immune and inflammatory responses in mice.

Toxoplasma gondii is an obligate intracellular parasite that causes severe illness in infants infected during pregnancy and in immunocompromised individuals. This parasite manipulates host cells through effector proteins that promote its survival and replication. While the phosphatases in the PP2C family have been shown to regulate host immune responses and contribute to the virulence and pathogenicity of various pathogens, the specific biological functions of PPM3H in T. gondii and its role in host-pathogen interactions remain unclear. In this study, we demonstrate that knockout of ppm3h significantly reduces the virulence and pathogenicity of T. gondii. In contrast, that high expression of ppm3h in the less virulent PRU induced by replacing the ppm3h gene elements of RH strain can enhance its pathogenicity, indicating a direct contribution of PPM3H to virulence in expression-independent manner. Furthermore, PPM3H significantly influenced host gene expression, with differentially expressed genes predominantly enriched in immune and inflammatory pathways. Weighted gene co-expression network analysis identified host immune genes, including chemokines such as Cx3cl1 and Ccl22, as co-expressed with ppm3h. Also, ppm3h co-expressed with T. gondii rhoptry genes including rop18, a well-known virulence factor, suggesting a role for PPM3H in coordinating host-pathogen interactions. Our findings establish that PPM3H enhances T. gondii virulence by modulating the host immune and inflammatory responses. PPM3H does not impact parasite gene expression, invasion or replication in vitro, supporting its role as an immune modulator rather than a general fitness factor. This suggests that T. gondii's pathogenicity arises not only from immune evasion but also from the active induction of host immune and inflammatory responses mediated by PPM3H.