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Sporozoite-Mediated Hepatocyte Wounding Limits Plasmodium Parasite Development via MyD88-Mediated NF-B Activation and Inducible NO Synthase Expression¹

Department of Biochemistry, University of Lausanne, Epalinges, Switzerland

Plasmodium sporozoites traverse several host cells before infecting hepatocytes. In the process, the plasma membranes of the cells are ruptured, resulting in the release of cytosolic factors into the microenvironment. This released endogenous material is highly stimulatory/immunogenic and can serve as a danger signal initiating distinct responses in various cells. Thus, our study aimed at characterizing the effect of cell material leakage during Plasmodium infection on cultured mouse primary hepatocytes and HepG2 cells. We observed that wounded cell-derived cytosolic factors activate NF-B, a main regulator of host inflammatory responses, in cells bordering wounded cells, which are potential host cells for final parasite infection. This activation of NF-B occurred shortly after infection and led to a reduction of infection load in a time-dependent manner in vitro and in vivo, an effect that could be reverted by addition of the specific NF-B inhibitor BAY11-7082. Furthermore, no NF-B activation was observed when Spect^–/– parasites, which are devoid of hepatocyte traversing properties, were used. We provide further evidence that NF-B activation causes the induction of inducible NO synthase expression in hepatocytes, and this is, in turn, responsible for a decrease in Plasmodium-infected hepatocytes. Furthermore, primary hepatocytes from MyD88^–/– mice showed no NF-B activation and inducible NO synthase expression upon infection, suggesting a role of the Toll/IL-1 receptor family members in sensing cytosolic factors. Indeed, lack of MyD88 significantly increased infection in vitro and in vivo. Thus, host cell wounding due to parasite migration induces inflammation which limits the extent of parasite infection.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by Lausanne University Institutional funds.

² Address correspondence and reprint requests to Dr. G. Corradin, Department of Biochemistry, Chemin des Boveresses 155, 1066 Epalinges, Switzerland. E-mail address: Giampietro.Corradin{at}unil.ch

³ Abbreviations used in this paper: hsp, heat-shock protein; iNOS, inducible NO synthase; spz, sporozoites; sgm, homogenized salivary gland; PI, propidium iodide; DAPI, 4',6-diamidino-2-phenylindole, dihydrochloride; PbCSP, P. berghei circumsporozoite protein; EEFs, exoerythrocytic form; SN spz, supernatant of infected hepatocyte; SN MC, filtered supernatant of mechanically wounded cell; SMT, S-methylisothiourea sulfate; DN, dominant negative; CSP, circumsporozoite protein.