Roles of free GPIs in amastigotes of Leishmania

Glycosylated phosphatidylinositols (GPIs) are abundant cell surface molecul es of the Leishmania. Amastigote-specific GPIs AmGPI-Y and AmGPI-Z, both et hanolamine (EtN)-containing glycolipids, were identified in Leishmania amaz onensis. A paucity of GPI-anchored proteins in amastigotes of L. amazonensi s made the kinetoplastid suitable for evaluating the importance of free (i. e. unconjugated to protein or polysaccharide) GPIs. A strain deficient in b oth AmGPI-Y and AmGPI-Z was produced by stable transfection of wild-type Le ishmania with a GPI-phospholipase C gene. Phosphatidylinositol deficiency w as not detected in the transfectants. GPI-deficient promastigotes infected murine macrophages in vitro and differentiated into amastigotes whose growt h was arrested within the host cells. Cytostasis of amastigotes was also ob served during axenic culture of GPI-deficient parasites. In a hamster model of leishmaniasis, GPI-deficient promastigotes produced smaller lesions wit h 20-fold fewer amastigotes than infections with control parasites. Togethe r, these observations indicate that EtN-GPIs may be essential for amastigot e viability, replication, and/or virulence. Implicit in these observations is the notion that drugs targeted against the GPI biosynthetic pathway migh t be of value in the management of human leishmaniasis. (C) 1999 Elsevier S cience B.V. All rights reserved.