Role of β-D-galactofuranose in Leishmania major macrophage invasion

The role of glycosylinositol phospholipid 1 (GIPL-1) of Leishmania (Leishmania) major in the interaction of promastigotes and amastigotes with macrophages was analyzed. Monoclonal antibody MEST-1, which recognizes glycolipids containing terminal galactofuranose (Galf) residues (E. Suzuki, A S. Toledo, H. K. Takahashi, and A. H. Straus, Glycobiology 7:463-468, 1997), was used to detect GIPL-1 in Leishmania by indirect immunofluorescence and to analyze its role in macrophage infectivity. L. major promastigotes showed intense fluorescence with MEST-1, and GIPL-1 was detected in both amastigote and promastigote forms by high-performance thin-layer chromatography immunostaining by using MEST-1. Delipidation of L. major promastigotes with isopropanol-hexane-water eliminated the MEST-1 reactivity, confirming that only GIPL-1 is recognized in either amastigotes or promastigotes of this species. The biological role of GIPL-1 in the ability of L. major to invade macrophages was studied by using either Fab fragments of MEST-1 or methylglycosides. Preincubation of parasites with Fab fragments reduced macrophage infectivity in about 80% of the promastigotes and 30% of the amastigotes. Preincubation of peritoneal macrophages with p-nitrophenyl-beta-galacto-furanoside (10 mM) led to significant (similar to80%) inhibition of promastigote infectivity. These data suggest that a putative new receptor recognizing beta-D-Galf is associated with L. major macrophage infectivity and that GIPL-1 containing a terminal Galf residue is involved in the L. major-macrophage interaction.