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Conservation of CD1 intracellular trafficking patterns between mammalian species
Christopher C Dascher1, Kenji Hiromatsu, Xiaowei Xiong
1Division of Rheumatology, Immunology and Allergy, Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA. cdascher@rics.bwh.harvard.edu
Insights
Guinea pig dendritic cells (DCs) express CD1 proteins, similar to humans. These CD1 molecules traffic differently within DCs, allowing for the presentation of lipid antigens from various cellular compartments.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Dendritic cells (DCs) are crucial antigen-presenting cells (APCs) that present antigens (Ags) to T cells.
- CD1 molecules, particularly group 1 CD1 isoforms, present lipid and glycolipid antigens.
- Human CD1 isoforms traffic to distinct endocytic compartments within DCs.
Purpose of the Study:
- To investigate the expression and trafficking patterns of guinea pig CD1 (gpCD1) isoforms on isolated DCs.
- To compare gpCD1 trafficking with known human CD1 isoform trafficking.
- To understand the functional implications of gpCD1 localization for lipid antigen sampling.
Main Methods:
- Utilized confocal microscopy with isoform-specific monoclonal antibodies (mAbs) to visualize gpCD1 localization.
- Assessed colocalization of gpCD1 isoforms with MHC class II to determine endosomal compartments.
- Incubated DCs with Mycobacterium tuberculosis lipoarabinomannan (LAM) to study lipid antigen uptake and presentation.
Main Results:
- Two distinct gpCD1b isoforms exhibited differential trafficking patterns within guinea pig DCs.
- gpCD1b1 colocalized with MHC class II in late endosomes, suggesting endosomal localization.
- gpCD1b3 remained on the cell surface and did not colocalize with endocytosed LAM, unlike gpCD1b1.
Conclusions:
- Guinea pig DCs express gpCD1 isoforms with unique trafficking behaviors mirroring human CD1 isoforms.
- Differential trafficking allows gpCD1 molecules to access distinct cellular compartments for lipid antigen sampling.
- These findings suggest a conserved evolutionary mechanism for CD1-mediated lipid antigen presentation across mammals.
Abstract:
Dendritic cells (DC) are potent APCs that sample Ags from the surrounding environment and present them to naive T cells using cell surface Ag-presenting molecules. The DC in both lymphoid and nonlymphoid tissues express high levels of CD1, a cell surface glycoprotein capable of presenting lipids and glycolipids to T cells. Distinct group 1 CD1 isoforms (CD1a, -b, -c) in man are known to traffic to different parts of the endocytic system where microbial Ags may be sampled. Guinea pigs are the only known rodent species that express the group 1 CD1 proteins. Therefore, we examined the expression and trafficking of guinea pig CD1 (gpCD1) isoforms on isolated DC. Confocal microscopy using mAbs specific for individual gpCD1 isoforms revealed differential trafficking of two distinct CD1b isoforms within DC. Colocalization of MHC class II was observed with the gpCD1b1 isoform, consistent with localization in the late endosomes of DC. In contrast, the gpCD1b3 isoform lacks an endosomal sorting motif and remains on the cell surface. Following incubation with Mycobacterium tuberculosis lipoarabinomannan, colocalization of endocytosed lipoarabinomannan with the gpCD1b1 isoform was observed but not with the gpCD1b3 isoform, which remained primarily on the cell surface. These data demonstrate that guinea pig DC express CD1 isoforms with unique trafficking patterns that recapitulate the patterns seen for human CD1 isoforms. This suggests evolutionary pressure for a conserved mechanism in mammals that allows CD1 to sample lipid Ags from various subcompartments of the endocytic system.
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