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Presentation of Leishmania donovani promastigotes occurs via a brefeldin A-sensitive pathway
1Department of Medical Parasitology, London School of Hygiene and Tropical Medicine.
Abstract:
For the presentation of Leishmania promastigotes to polyclonal CD4+ T cells, a processing period within activated macrophages of 3-4 h is required. Presentation can be inhibited by both chloroquine and brefeldin A (BFA), the latter implicating a requirement for newly synthesized MHC class II molecules. This inhibition is both reversible and specific, in that BFA did not inhibit mixed lymphocyte reaction stimulation by these infected macrophages. Immunogold labeling demonstrated that class II was associated with the parasite-containing phagolysosome. The level of class II was not significantly altered in BFA-treated cells in the time period studied, suggesting that antigen may exist the phagolysosome and interact with class II in another cellular compartment.
Insights
Leishmania promastigotes require macrophage processing for CD4+ T cell presentation. Newly synthesized MHC class II molecules are crucial, with antigen potentially moving from phagolysosomes for interaction.
Area of Science:
- Immunology
- Cell Biology
- Parasitology
Background:
- Leishmania parasites infect macrophages, a key step in initiating adaptive immune responses.
- Antigen presentation by macrophages to T cells is critical for orchestrating immune defense against pathogens.
Purpose of the Study:
- To investigate the cellular mechanisms and kinetics of Leishmania antigen presentation by macrophages to CD4+ T cells.
- To determine the role of newly synthesized MHC class II molecules in this process.
Main Methods:
- Macrophage infection with Leishmania promastigotes.
- Inhibition studies using chloroquine and brefeldin A (BFA).
- Immunogold labeling and electron microscopy for MHC class II localization.
Main Results:
- A 3-4 hour processing period in macrophages is necessary for Leishmania antigen presentation.
- BFA, inhibiting new MHC class II synthesis, reversibly blocked presentation, indicating its requirement.
- MHC class II was found associated with parasite-containing phagolysosomes, but antigen might exit this compartment for interaction.
Conclusions:
- Newly synthesized MHC class II molecules are essential for Leishmania antigen presentation.
- Antigen processing and presentation likely involve compartments beyond the initial phagolysosome.