title: Elevated levels of the Plasmodium yoelii homologue of macrophage migration inhibitory factor attenuate blood-stage malaria.
abstract: The excessive production of proinflammatory cytokines plays a significant role in the pathogenesis of severe malaria. Mammalian macrophage migration inhibitory factor (MIF) (mMIF) is an immune mediator that promotes a sustained proinflammatory response by inhibiting the glucocorticoid-mediated downregulation of inflammation. In addition, Plasmodium parasites also encode a homologue of mammalian MIF that is expressed in asexual-stage parasites. We used the Plasmodium yoelii murine model to study the potential role of parasite-encoded MIF in the pathogenesis of malaria. Antibodies raised against purified, non-epitope-tagged P. yoelii MIF (PyMIF) were used to localize expression in trophozoite- and schizont-stage parasites and demonstrate extracellular release. In vitro, recombinant PyMIF was shown to actively induce the chemotaxis of macrophages but did not induce or enhance tumor necrosis factor alpha (TNF-α) production from peritoneal macrophages. To examine the role of parasite-derived PyMIF in vivo, two transgenic parasite lines that constitutively overexpress PyMIF were generated, one in a nonlethal P. yoelii 17X background [Py17X-MIF(+)] and the other in a lethal P. yoelii 17XL background [Py17XL-MIF(+)]. Challenge studies with transgenic parasites in mice showed that the increased expression of PyMIF resulted in a reduction in disease severity. Mice infected with Py17X-MIF(+) developed lower peak parasitemia levels than controls, while malaria-associated anemia was unaltered. Infection with Py17XL-MIF(+) resulted in a prolonged course of infection and a reduction in the overall mortality rate. Combined, the data indicate that parasite-derived MIF does not contribute significantly to immunopathology but, through its chemotactic ability toward macrophages, may attenuate disease and prolong infection of highly virulent parasite isolates.
authors.affiliation: Center for Molecular Parasitology, Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, PA 19129, USA.
authors.forename: Swati
authors.initials: S
authors.lastname: Thorat
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Daly
authors.forename: Lawrence W
authors.initials: LW
authors.lastname: Bergman
authors.forename: James M
authors.initials: JM
authors.lastname: Burns
mesh_terms: D000818:Animals; D000913:Antibodies, Protozoan / Q000276:immunology; D019084:Fluorescent Antibody Technique, Indirect; D008263:Macrophage Migration-Inhibitory Factors / Q000276:immunology* / Q000502:physiology; D008264:Macrophages / Q000276:immunology / Q000502:physiology; D008288:Malaria / Q000276:immunology* / Q000469:parasitology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D010967:Plasmodium yoelii / Q000276:immunology* / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology / Q000502:physiology
chemical_list: D000913:Antibodies, Protozoan; D008263:Macrophage Migration-Inhibitory Factors; D014409:Tumor Necrosis Factor-alpha