Anti-Infection Roles of mir155-5p Packaged in Exosomes Secreted by Dendritic Cells Infected with Toxoplasma Gondii

Background: Toxoplasma gondii is a zoonotic intracellular protozoon that is estimated to infect about 30% of the world’s population, resulting in toxoplasmosis in immuno-compromised patients and adverse outcomes in the primary infection during pregnancy. Exosomes are tubular vesicles secreted by cells, and they function in intercellular communication. It has been reported that the exosomes secreted by T. gondii- infected immune cells transmit infection signals to the uninfected cells. However, the mechanism and effect of the exosome transmission are still vague. We therefore investigated the function of the exosomes transmitted from DC2.4 cells infected with T. gondii RH strain ( Tg -DC-Exo) to the uninfected cells, as well as their roles in anti-infection. Methods: : We conducted exosome isolation and identification with ultracentrifugation, transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA) and Western blotting. Recipient cells taken up exosomes by PKH67 assay. The signal transmission and the abundance of mir155-5p were determined using transwell assay and qRT-PCR. For the immune responses, cytokines was evaluated. T. gondii B1 gene was determined to evaluate tachyzoites proliferation. Results: : We observed that Toxoplasma infection up-regulated mir155-5p expression in DC2.4 cells secreted exosomes, and those exosomes can be ingested by murine macrophage RAW264.7 cells. Tg -DC-Exo and mir155-5p stimulating host proinflammatory immune responses such as proinflammatory cytokine (IL6,iNOS and TNF-α) production increased and NF-κB signal pathway activation by down regulating SOCS1, leading to inhibit T. gondii tachyzoite proliferation in RAW264.7 cells. Conclusion: Our findings provide a novel mechanism for how infected cells transmit infection signals to the uninfected cells through exosome secretion after T. gondii infection, followed by inflammatory responses and anti-infection reactions, which may help us develop a new intervention strategy for toxoplasmosis prevention, especially in immuno-compromised patients.