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Identification of a macrophage-binding determinant on lipophosphoglycan from Leishmania major promastigotes
M Kelleher1, A Bacic, E Handman
1Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria, Australia.
Abstract:
Leishmania are obligatory intracellular parasites in mammalian macrophages that gain entry by receptor-mediated phagocytosis. Their major cell surface glycoconjugate, lipophosphoglycan (LPG), has been implicated in this process. A monoclonal antibody specific for Leishmania major LPG (WIC 79.3), which has been shown to block promastigote attachment to macrophages, was used to identify a macrophage-binding determinant of LPG. WIC 79.3 bound exclusively to the phosphorylated repeats of LPG and not to the saccharide core or lipid anchor. Furthermore, the epitope recognized by WIC 79.3 mapped to the phosphorylated oligosaccharide P5b, PO4-6[Gal(beta 1-3)Gal(beta 1-3)Gal(beta 1-3)]Gal(beta 1-4)Man(alpha 1-, which is unique to the LPG of promastigotes of L.major. Phosphorylated oligosaccharides P3, PO4-6[Gal(beta 1-3)[Gal(beta 1-4) Man(alpha 1-, and P4b, PO4-6[Gal(beta 1-3)Gal(beta 1-3)] Gal(beta 1-4)Man(alpha 1-, were also recognized by WIC 79.3 but with considerably lower (approximately 100-fold) affinities. The phosphorylated oligosaccharide P5b inhibited attachment of promastigotes of L. major to the macrophage cell line J774 to the same degree as phosphoglycan (derived from LPG) and Fab fragments of WIC 79.3, suggesting that P5b is a site of L. major LPG that is recognized by macrophage receptor(s) and is an important determinant in the attachment of promastigotes to host macrophages and initiation of infection.
Insights
Leishmania parasites use lipophosphoglycan (LPG) to attach to macrophages. A specific antibody identified a key LPG structure, P5b, crucial for parasite entry and infection initiation.
Area of Science:
- Parasitology
- Immunology
- Glycobiology
Background:
- Leishmania are intracellular parasites that infect macrophages.
- Lipophosphoglycan (LPG) is a key Leishmania surface molecule involved in host cell entry.
- Understanding LPG's role in macrophage attachment is vital for controlling infection.
Purpose of the Study:
- To identify the specific macrophage-binding determinant on Leishmania major LPG.
- To investigate the role of LPG's phosphorylated repeats in parasite attachment.
Main Methods:
- Utilized a monoclonal antibody (WIC 79.3) specific to Leishmania major LPG.
- Analyzed LPG binding to phosphorylated repeats, saccharide core, and lipid anchor.
- Mapped the epitope recognized by WIC 79.3 to specific phosphorylated oligosaccharides.
Main Results:
- The antibody WIC 79.3 exclusively bound to phosphorylated repeats of LPG.
- The epitope P5b, unique to L. major promastigote LPG, was identified as a high-affinity binding site.
- P5b significantly inhibited Leishmania attachment to macrophages, similar to whole LPG fragments.
Conclusions:
- The phosphorylated oligosaccharide P5b is a critical determinant for Leishmania major attachment to macrophages.
- P5b is recognized by macrophage receptors, mediating parasite entry.
- This finding highlights P5b as a potential target for anti-Leishmania therapies.