Apicomplexan protozoan pathogens avoid destruction and establish a replicative niche within host cells by forming a nonfusogenic parasitophorous vacuole (PV). Here we present evidence for lysosome-mediated degradation of Toxoplasma gondii after invasion of macrophages activated in vivo. Pathogen elimination was dependent on the interferon γ inducible-p47 GTPase, IGTP, required PI3K activity, and was preceded by PV membrane indentation, vesiculation, disruption, and, surprisingly, stripping of the parasite plasma membrane. Denuded parasites were enveloped in autophagosome-like vacuoles, which ultimately fused with lysosomes. These observations outline a series of mechanisms used by effector cells to redirect the fate of a classically nonfusogenic intracellular pathogen toward a path of immune elimination.

Objective-Microvesicles have been shown to mediate intercellular communication. Previously, we have correlated entry of murine lung-derived microvesicles into murine bone marrow cells with expression of pulmonary epithelial cell-specific mRNA in these marrow cells. The present studies establish that entry of lung-derived microvesicles into marrow cells is a prerequisite for marrow expression of pulmonary epithelial cell-derived mRNA.Methods/Results-Murine bone marrow cells co-cultured with rat lung, but separated from them using a cell-impermeable membrane (0.4 micron pore size), were analyzed using species-specific primers (for rat or mouse). These studies revealed that surfactant B and C mRNA produced by murine marrow cells were of both rat and mouse origin. Similar results were obtained using murine lung cocultured with rat bone marrow cells or when bone marrow cells were analyzed for the presence of species-specific albumin mRNA after co-culture with rat or murine liver. These studies show that microvesicles both deliver mRNA to marrow cells and also mediate marrow cell transcription of tissue-specific mRNA. The latter likely underlies the longer term stable change in genetic phenotype which has been observed. We have also observed microRNA in lung-derived microvesicles and Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Conflict of interest disclosureNo financial interest/relationships with financial interest relating to the topic of this article have been declared. studies with RNase-treated microvesicles indicate that microRNA negatively modulates pulmonary epithelial cell-specific mRNA levels in co-cultured marrow cells. In addition, we have also observed tissue-specific expression of brain, heart and liver mRNA in co-cultured marrow cells suggesting that microvesicle-mediated cellular phenotype change is a universal phenomena. NIH Public AccessConclusion-These studies suggest that cellular systems are more phenotypically labile then previously considered.

Apicomplexan protozoan pathogens avoid destruction and establish a replicative niche within host cells by forming a nonfusogenic parasitophorous vacuole (PV). Here we present evidence for lysosome-mediated degradation of Toxoplasma gondii after invasion of macrophages activated in vivo. Pathogen elimination was dependent on the interferon inducible-p47 GTPase, IGTP, required PI3K activity, and was preceded by PV membrane indentation, vesiculation, disruption, and, surprisingly, stripping of the parasite plasma membrane. Denuded parasites were enveloped in autophagosome-like vacuoles, which ultimately fused with lysosomes. These observations outline a series of mechanisms used by effector cells to redirect the fate of a classically nonfusogenic intracellular pathogen toward a path of immune elimination. CORRESPONDENCE George S. Yap: George_Yap@brown.eduThe online version of this article contains supplemental material.

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