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Saposin C is required for lipid presentation by human CD1b
Florian Winau1, Vera Schwierzeck, Robert Hurwitz
1Max-Planck-Institute for Infection Biology, Department of Immunology, Schumannstrasse 21-22, D-10117 Berlin, Germany.
Nature Immunology
|January 13, 2004
Summary
Sphingolipid activator protein-C (SAP-C) is crucial for presenting Mycobacterium tuberculosis lipids to T cells via CD1b. This study identifies SAP-C as the missing molecule in this essential immune pathway.
Area of Science:
- Immunology
- Molecular Biology
- Microbiology
Background:
- Lipid antigens from Mycobacterium tuberculosis are presented to human T lymphocytes by CD1 proteins.
- The accessory molecules involved in lipid antigen loading onto CD1b remain unidentified.
Purpose of the Study:
- To identify the accessory molecules required for CD1b-mediated presentation of lipid antigens.
- To elucidate the mechanism of lipid antigen loading onto CD1b.
Main Methods:
- Fibroblasts deficient in sphingolipid activator proteins (SAPs) were transfected with CD1b.
- T cell activation assays were performed using lipid-specific T cells.
- Liposome-based assays and coprecipitation were used to investigate molecular interactions.
Main Results:
- Fibroblasts lacking SAPs failed to activate lipid-specific T cells, but reconstitution with SAP-C restored T cell responses.
- SAP-C was found to colocalize with lipid antigens in lysosomal compartments.
- SAP-C demonstrated efficient extraction of lipid antigens from membranes and direct interaction with CD1b.
Conclusions:
- SAP-C is essential for the presentation of lipid antigens via CD1b to human T cells.
- SAP-C acts by exposing lipid antigens from intralysosomal membranes for loading onto CD1b.
- SAP-C represents a critical, previously unidentified component of the CD1b antigen presentation pathway.