Published online before print January 27, 2009

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(Journal of Leukocyte Biology. 2009;85:877-885.)
© 2009 Society for Leukocyte Biology

Balance of Irgm protein activities determines IFN--induced host defense

Stanley C. Henry^*, Xiaoju G. Daniell, Ashley R. Burroughs, Maanasa Indaram, David N. Howell, Jörn Coers, Michael N. Starnbach, Julia P. Hunn^||, Jonathan C. Howard^||, Carl G. Feng^¶, Alan Sher^¶ and Gregory A. Taylor^*,,1

^* Geriatric Research, Education, and Clinical Center, VA Medical Center, Durham, North Carolina, USA;
Departments of Medicine, Molecular Genetics and Microbiology and Immunology, Division of Geriatrics, and Center for the Study of Aging and Human Development, Duke University Medical Center, Durham, North Carolina, USA;
Department of Pathology, Duke University and VA Medical Centers, Durham, North Carolina, USA;
Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts, USA;
^|| Institute for Genetics, University of Cologne, Cologne, Germany; and
^¶ Immunobiology Section, Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland, USA

¹ Correspondence: VA Medical Center, 508 Fulton Street, Room N3008, Durham, NC 27705, USA. E-mail: gregory.taylor{at}duke.edu

ABSTRACT

The immunity-related GTPases (IRG), also known as p47 GTPases, are a family of proteins that are tightly regulated by IFNs at the transcriptional level and serve as key mediators of IFN-regulated resistance to intracellular bacteria and protozoa. Among the IRG proteins, loss of Irgm1 has the most profound impact on IFN--induced host resistance at the physiological level. Surprisingly, the losses of host resistance seen in the absence of Irgm1 are sometimes more striking than those seen in the absence of IFN-. In the current work, we address the underlying mechanism. We find that in several contexts, another protein in the IRG family, Irgm3, functions to counter the effects of Irgm1. By creating mice that lack Irgm1 and Irgm3, we show that several phenotypes important to host resistance that are caused by Irgm1 deficiency are reversed by coincident Irgm3 deficiency; these include resistance to Salmonella typhimurium in vivo, the ability to affect IFN--induced Salmonella killing in isolated macrophages, and the ability to regulate macrophage adhesion and motility in vitro. Other phenotypes that are caused by Irgm1 deficiency, including susceptibility to Toxoplasma gondii and the regulation of GKS IRG protein expression and localization, are not reversed but exacerbated when Irgm3 is also absent. These data suggest that members of the Irgm subfamily within the larger IRG family possess activities that can be opposing or cooperative depending on the context, and it is the balance of these activities that is pivotal in mediating IFN--regulated host resistance.

Key Words: interferon • resistance • p47 GTPases

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