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Assembly of an abundant endogenous major histocompatibility complex class II/peptide complex in class II compartments
S Morkowski1, G Raposo, M Kleijimeer
1Department of Immunology, University of Washington School of Medicine, Seattle 98195, USA.
Insights
Human B lymphocytes form major histocompatibility complex class II/peptide complexes within specialized compartments. These complexes transiently accumulate in these compartments before moving to the cell surface.
Area of Science:
- Immunology
- Cell Biology
Background:
- Major histocompatibility complex (MHC) class II molecules present peptide antigens to T helper cells, a critical step in adaptive immunity.
- Understanding the intracellular assembly and trafficking of MHC class II/peptide complexes is crucial for immune response regulation.
Purpose of the Study:
- To pinpoint the intracellular location where endogenous class II/peptide complexes are formed in human B lymphocytes.
- To elucidate the assembly pathway and transient accumulation sites of these complexes before cell surface expression.
Main Methods:
- Kinetic pulse-chase labeling experiments were performed on a human B cell line.
- Subcellular fractionation was achieved using Percoll density gradient centrifugation.
- Immunogold labeling on ultrathin cryosections and the monoclonal antibody YAe were used to detect specific class II/peptide complexes.
Main Results:
- Class II/peptide complexes were shown to assemble intracellularly in human B lymphocytes.
- These complexes were observed to transiently accumulate in compartments enriched for MHC class II molecules.
- The study demonstrated the pathway from intracellular assembly to cell surface presentation.
Conclusions:
- MHC class II/peptide complexes assemble and initially accumulate in MHC class II-enriched compartments within human B lymphocytes.
- This intracellular trafficking pathway precedes the surface expression of these immune-critical complexes.
- The findings provide insights into the biogenesis and presentation of antigens by B cells.
Abstract:
To identify the intracellular site(s) of formation of an endogenous class II/peptide complex in a human B cell line, we employed kinetic pulse-chase labeling experiments followed by subcellular fractionation by Percoll density gradient centrifugation and immunogold labeling on ultrathin cryosections. For direct demonstration of assembly of such complexes, we used the monoclonal antibody YAe, which detects an endogenous complex of the mouse class II molecule I-Ab with a 17-amino acid peptide derived from the alpha chain of HLA-DR (DR alpha52-68). We show that in human B lymphocytes, these class II/peptide complexes assemble and transiently accumulate in major histocompatibility complex class II-enriched compartments before reaching the cell surface.