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Updated: Jul 26, 2026
A Microscopic Phenotypic Assay for the Quantification of Intracellular Mycobacteria Adapted for High-throughput/High-content Screening
Published on: January 17, 2014
Intersection of group I CD1 molecules and mycobacteria in different intracellular compartments of dendritic cells
U E Schaible1, K Hagens, K Fischer
1Department of Immunology, Max Planck Institute for Infection Biology, Berlin, Germany. schaible@mpiib-berlin.mpg.de
Insights
Human CD1a, CD1b, and CD1c molecules present mycobacterial glycolipids to T cells. These CD1 molecules access mycobacterial glycolipids at distinct intracellular locations, impacting antigen presentation during infection.
Area of Science:
- Immunology
- Cell Biology
Background:
- Human CD1 molecules (CD1a, CD1b, CD1c) present mycobacterial glycolipids to T cells.
- Phagosomes with viable mycobacteria are early endosomal compartments, crucial for antigen processing.
Purpose of the Study:
- To investigate the intracellular localization of CD1 molecules and mycobacterial glycolipids in infected antigen-presenting cells (APCs).
- To understand how different CD1 molecules interact with mycobacterial antigens at various cellular compartments.
Main Methods:
- Immunofluorescence microscopy to track CD1 localization and mycobacterial phagosomes in infected APCs.
- Analysis of CD1 molecule distribution within early endosomes, late endosomes/lysosomes, and phagolysosomes.
Main Results:
- CD1a and CD1c localize to early endosomes and the cell surface, while CD1b is found in late endosomes/lysosomes and mature phagolysosomes.
- Released glycolipids are transported from phagosomes to late endosomes/lysosomes and bystander cells.
- The macrophage mannose receptor is not found in mycobacterial phagosomes, suggesting a different role in glycolipid trafficking.
Conclusions:
- All three CD1 molecules (CD1a, CD1b, CD1c) interact with mycobacteria and their glycolipids.
- Differential localization of CD1 molecules allows sampling of mycobacterial glycolipids from distinct intracellular sites.
- This compartmentalization influences the processing and presentation of mycobacterial antigens, with implications for T cell responses in mycobacterial infections.
Abstract:
Human CD1a, CD1b, and CD1c molecules can present mycobacterial glycolipids to T cells. Because phagosomes containing viable mycobacteria represent early endosomal compartments, we studied where mycobacterial glycolipids intersect with CD1 molecules in infected APC. CD1b and CD1c, but not CD1a, localized to late endosomes/lysosomes. CD1a and CD1c were predominantly expressed on the cell surface and in mycobacterial phagosomes of the early endosomal stage. In contrast, CD1b was present in a subset of mycobacterial phagosomes representing mature phagolysosomes. Released mycobacterial glycolipids including lipoarabinomannan and phosphatidylinositol mannosides were transported from the phagosome into late endosomes/lysosomes and to uninfected bystander cells. The macrophage mannose receptor, which has been implicated in glycolipid uptake by APC for CD1b-mediated presentation, was absent from mycobacterial phagosomes and may therefore not be involved in trafficking of glycolipids between phagosomes and late endosomes/lysosomes. In conclusion, all three CD1 molecules have access to mycobacteria and glycolipids thereof, but at different intracellular sites. This allows sampling by CD1a, CD1b, and CD1c of mycobacterial glycolipids from different intracellular sites of the infected cell, which has important implications for processing and presentation of such Ags during mycobacterial infections.
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