Biphasic Regulation of TLR7/MyD88/IRF7-IFN-β Axis by Toxoplasma gondii Facilitates Immune Evasion

Toxoplasma gondii (T. gondii) is a remarkably successful intracellular parasite, largely because of its ability to manipulate host immune response. Toll-like receptor 7 (TLR7), a sensor for single-stranded RNA, plays a crucial role in resistance to viral infections, but its function during T. gondii infection remains unclear. In this study, we investigated the role and regulation of the TLR7/MyD88/IRF7 signaling pathway during T. gondii infection. RNA-seq, qRT-PCR, and Western blot analyses revealed significant downregulation of Tlr7 expression in RAW264.7 cells at 24 h post-infection (hpi). Additionally, treatment with the TLR7 agonist imiquimod suppressed T. gondii proliferation in vitro and prolonged survival in infected mice. Time-course analysis uncovered a biphasic regulation of the TLR7/MyD88/IRF7 pathway: during the early infection phase (8 hpi in vitro or 12 hpi in vivo), these components were rapidly upregulated, along with a significant increase in IFN-β mRNA levels. However, as the infection progressed (12-24 hpi in vitro or 24-96 hpi in vivo), the expression of these pathway components and IFN-β declined. Crucially, siRNA-mediated knockdown of Tlr7 abolished this biphasic regulation and significantly suppressed downstream Irf7 and Ifnb1 expression, establishing TLR7 as essential for pathway activation and IFN-β induction. This biphasic regulation of the pathway by T. gondii in RAW264.7 cells has not been previously reported. This study helps elucidate the role of Toll-like receptors during T. gondii infection of the host and provides a new strategy for the treatment of T. gondii.