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Biosynthesis of lymphocyte surface IgD in the mouse
Journal of Immunology (Baltimore, Md. : 1950)
|June 1, 1980
Summary
Immunoglobulin D (IgD) is synthesized as a basic, incompletely glycosylated precursor in mouse spleen cells. It undergoes modifications, including the addition of sialic acid and galactose, before appearing on the cell surface.
Area of Science:
- Immunology
- Molecular Biology
- Glycobiology
Background:
- Immunoglobulin D (IgD) is a key B cell receptor, but its synthesis and post-translational modifications are not fully elucidated.
- Understanding IgD synthesis is crucial for comprehending B cell development and immune responses.
Purpose of the Study:
- To investigate the synthesis and processing of Immunoglobulin D (IgD) in mouse spleen cells.
- To characterize the molecular changes IgD undergoes from synthesis to cell surface expression.
Main Methods:
- [35S]methionine labeling of mouse spleen cells.
- Immunoprecipitation using monoclonal antibodies against IgD.
- Two-dimensional gel electrophoresis.
- Enzymatic treatments (pronase, neuraminidase, endoglycosidase H).
- Lectin binding assays (lentil lectin, Ricinus communis hemagglutinin).
Main Results:
- A basic precursor form (IgD1) with high mannose oligosaccharides was identified.
- Acidic forms (IgD2) with added sialic acid and galactose were observed during a chase period.
- IgD1 was sensitive to endoglycosidase H, while IgD2 was resistant.
- Surface IgD (IgD2) showed specific binding to Ricinus communis hemagglutinin, indicating terminal galactose residues.
Conclusions:
- IgD is synthesized as an incompletely glycosylated precursor with high mannose oligosaccharides.
- Processing involves the addition of galactose and sialic acid shortly before surface expression.
- IgD exhibits slow intracellular transit and is not secreted in detectable amounts.