The role(s) of lipophosphoglycan (LPG) in the establishment of Leishmania major infections in mammalian hosts

doi:10.1073/pnas.1530604100

The role(s) of lipophosphoglycan (LPG) in the establishment of Leishmania major infections in mammalian hosts

^*Department of Molecular Microbiology, Washington University Medical School, St. Louis, MO 63110; ^‡Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115; and ^§Department of Biochemistry, University of Kentucky Medical Center, Lexington, KY 40536

Edited by Louis H. Miller, National Institutes of Health, Rockville, MD (received for review January 30, 2003)

Abstract

The abundant cell surface glycolipid lipophosphoglycan (LPG) was implicated in many steps of the Leishmania infectious cycle by biochemical tests. The presence of other abundant surface or secreted glycoconjugates sharing LPG domains, however, has led to uncertainty about the relative contribution of LPG in vivo. Here we used an Leishmania major lpg1 ^- mutant, which lacks LPG alone and shows attenuated virulence, to dissect the role of LPG in the establishment of macrophage infections in vivo. lpg1 ^- was highly susceptible to human complement, had lost the ability to inhibit phagolysosomal fusion transiently, and was oxidant sensitive. Studies of mouse mutants defective in relevant defense mechanisms confirmed the role of LPG in oxidant resistance but called into question the importance of transient inhibition of phagolysosomal fusion for Leishmania macrophage survival. Moreover, the limited lytic activity of mouse complement appears to be an ineffective pathogen defense mechanism in vitro and in vivo, unlike human hosts. In contrast, lpg1 ^- parasites bound C3b and resisted low pH and proteases normally, entered macrophages efficiently and silently, and continued to inhibit host-signaling pathways. These studies illustrate the value of mechanistic approaches focusing on both parasite and host defense pathways in dissecting the specific biological roles of complex virulence factors such as LPG.

Footnotes

↵ ¶ To whom correspondence should be addressed at: Department of Molecular Microbiology, Washington University Medical School, Campus Box 8230, 660 South Euclid Avenue, St. Louis, MO 63110. E-mail: beverley{at}borcim.wustl.edu.
↵ † Present address: Department of Medical and Molecular Parasitology, New York University School of Medicine, New York, NY 10010.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: GIPLs, glycosylinositolphospholipids; GPI, glycosylphosphatidylinositol; LPG, lipophosphoglycan; LPS, lipopolysaccharide; moi, multiplicity of infection; NMMA, NG-monomethyl-l-arginine; PEMs, peritoneal exudate macrophages; PG, phosphoglycan; PPGs, proteophosphoglycans; RT, room temperature.