Extracellular Vesicles Secreted by Are Recognized by Toll-Like Receptor 2 and Modulate Host Cell Innate Immunity Through the MAPK Signaling Pathway

is an obligate intracellular parasite, which causes significant economic losses in the cattle industry. However, the immune mechanism of the parasite-host interaction is not yet fully understood. Extracellular vesicles (EVs) have emerged as a ubiquitous mechanism by which almost all cells, especially immune and tumor cells, participate in intercellular communications. Although studies have indicated that EVs secreted by or promote exchanges of biological molecules important for the host-parasite interplay, however, EVs and their biological activities in is not clear. Here, we used multiple methods, including electron microscopy, nanoparticle tracking analysis, RT-PCR, immunofluorescence, western blot, proteomics, and cytokine analyses, to examine the properties of EVs. We found that produced EVs that are similar to mammalian exosomes, which generally range from 30 to 150 nm in diameter. It was shown that EVs could remarkably increase the production of pro-inflammatory cytokines IL-12p40, TNF-α, IL-1β, IL-6, and IFN-γ by wild-type (WT) mouse bone marrow-derived macrophages (BMDMs) whereas the secretion of IL-12p40, TNF-α, and IFN-γ was very strongly downregulated in TLR2 mouse BMDMs. The levels of IL-6 were not affected, but the secretion of IL-10 was upregulated. We found that the phosphorylation levels of P38, ERK, and JNK were significantly reduced in the TLR2 cells compared with those in WT mouse BMDMs and that treatment with chemical inhibiters of P38, ERK, and JNK resulted in upregulation of IL-6, IL-12p40, and IL-10 production. Together, these results demonstrated that EVs could be rapidly internalized to deliver proteins to the host cells and modulate the host cell immune responses through MAPK signaling pathway in a TLR2-dependent manner. Our study is the first to reveal potential roles for EVs in host communication and immune response in parasite-host interactions.