Biological Properties Of Toxoplasma Gondii-Derived Exosomes And Its Immune Modulation On Host

Background:T.gondii is an obligate intracellular protozoan which infects all warm-blooded mammals including humans and livestock all over the world and causes serious zoonotic toxoplasmosis.This is harmful to human health and the development of animal husbandry.However,there are no ideal drugs or vaccines used to treat or prevent toxoplasmosis.Therefore,it is high time to illuminate the biological characteristic and pathogenesis of T.gondii as well as the design of new vaccines or therapeutic compounds against toxoplasmosis.Exosomes are 30-100 nm membrane-bound small vesicles that are released from several different cell or types.The exosomes from pathogens have somes special biological functions,such as mediating pathogens interacting with the host,regulating host immune responses.However,exosomes secreted by T.gondii have not yet been reported at present.Objectives:We described the isolation and characterization of exosomes from T.gondii RH and ME49 strain,respectively.This study evaluating the immunomodulatory and protective effects of T.gondii exosomes in macrophages and mice could shed light on the survival mechanisms of T.gondii in the host cells and might be a new drug or vaccine target.Methods:In this study,we isolated the exosomes from tachyzoites of T.gondii and identified the parasite-derived exosomes with electron microscopy and Western blotting.Then,we used PKH 67 dye(green fluorescence)labeling of T.gondii exosomes.After cells and T.gondii exosomes were cultured together,we observed whether the exosomes could flue with macrophages by fluorescence microscope.Then we explored that T.gondii exosomes whether regulate the viability and modulate the cytokines secretion by macrophages.Moreover,after BALB/c mice immunized with T.gondii exosomes,we detected of humoral immunity and cellular immune response for the immunized mice to test the power of parasites exosomes against acute T.gondii infection.Results:Our results demonstrated that T.gondii exosomes fused with and delivered their cargo to macrophages and modulated immune responses.The BALB/c mice immunized with T.gondii exosomes were elicited specific humoral responses by high titers of total IgG and IgG2a antibodies.T.gondii exosomes stimulated splenocytes cytokine responses by promoting IFN-? and IL-12 production indicating that a Thl-biased specific immune response was elicited after immunization with it.Furthermore,the percentages of CD8+ T cells were significantly increased in mice immunized with T.gondii exosomes,compared to PBS or Blank control groups(p<0.05).Then the mice challenged with the tachyzoites of low virulent T.gondii ME49 strain or high virulent RH strain significantly prolonged survival time.Conclusions:These findings demonstrated that T.gondii exosomes could provide protective immune responses(humoral and cellular immune responses)against parasitic infection in BALB/c mice,which suggested that exosomes may serve as a potential vaccine candidate against intracellular pathogens.