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Binding of Leishmania promastigotes to macrophages
Abstract:
Leishmania tropica promastigotes are easily attached to and engulfed by C3H peritoneal macrophages in vitro at 37 degrees C. Different sugars at 0.3-0.5 M inhibited in vitro the attachment of L. tropica promastigotes to C3H peritoneal macrophages with lactose (Gal-beta [1 leads to 4]Glc) being the most efficient. Inhibition of attachment is also affected by pre-treatment of promastigotes with galactose oxidase. Oligosaccharides extending from promastigote and amastigote cell surfaces contain an important proportion of non-reducing galactose as does the carbohydrate-rich factor (EF) excreted by promastigotes of L. tropica and L. donovani. This study suggests that Leishmania, an obligatory intracellular parasite, uses as a means of entering the host cell a cellular mechanism similar to that used in the removal of damaged cells from blood circulation. This mechanism is assumed to take advantage of the exposed sugars, particularly the exposed non-reducing galactose, on the parasite surface during the stage of attachment. Once the parasite is inside the cell, the EF it produces might have a protective function, being inhibitory to some of the host cell lysosomal enzymes.
Insights
Leishmania tropica parasites attach to host cells via exposed galactose sugars. This interaction, inhibited by specific sugars, suggests a mechanism similar to cellular debris removal for parasite entry.
Area of Science:
- Parasitology
- Cell Biology
- Immunology
Background:
- Leishmania tropica promastigotes readily attach to and are engulfed by C3H peritoneal macrophages in vitro.
- The interaction between Leishmania parasites and host macrophages is crucial for establishing infection.
Purpose of the Study:
- To investigate the role of surface sugars in the attachment of Leishmania tropica promastigotes to macrophages.
- To elucidate the mechanism by which Leishmania parasites enter host cells.
Main Methods:
- In vitro assays using C3H peritoneal macrophages and Leishmania tropica promastigotes.
- Inhibition studies with various sugars (e.g., lactose) and enzyme treatments (galactose oxidase).
- Analysis of oligosaccharides on parasite surfaces and excreted factors (EF).
Main Results:
- Attachment of promastigotes to macrophages was inhibited by specific sugars, with lactose being most effective.
- Pre-treatment of promastigotes with galactose oxidase also inhibited attachment.
- Parasite surface and excreted factors contain significant amounts of non-reducing galactose.
Conclusions:
- Leishmania parasites likely utilize exposed non-reducing galactose on their surface for attachment to host cells, mimicking mechanisms for damaged cell removal.
- The excreted factor (EF) may protect the parasite from host cell lysosomal enzymes after entry.