Abstract
We have recently reported that on human B lymphocytes, membrane IgM (mIgM) associates with a heterodimer of 47- and 37-kD polypeptides, the 47-kD subunit being encoded by the mb-1 gene. We show here that expression of mb-1, both at the mRNA and the protein level, is not restricted to IgM+ B cells but can also be found in IgM- pre-B cells and mIgM-IgG+ B cells. Membrane forms of IgD and IgG, isolated from freshly isolated human B cells and B cell lines, are expressed together with heterodimeric protein structures biochemically similar to the mIgM-associated polypeptides, and these were shown to comprise the products of the mb-1 and B29 genes, or homologous genes. Finally, all three classes of antigen receptors are linked to protein kinases, capable of phosphorylating the Ig-associated heterodimers. Our findings provide insight in the structural organization of the different antigen receptors on human B cells and have implications for their function.
MeSH terms
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Antibodies, Monoclonal
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B-Lymphocytes / immunology*
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Blotting, Northern
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Cell Line
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Cell Membrane / immunology
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Fluorescent Antibody Technique
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Genes, Immunoglobulin*
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Humans
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Immunoglobulin D / analysis
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Immunoglobulin D / genetics
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Immunoglobulin D / metabolism*
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Immunoglobulin G / analysis
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Immunoglobulin G / genetics
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Immunoglobulin G / metabolism*
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Immunoglobulin M / analysis
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Immunoglobulin M / genetics
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Immunoglobulin M / metabolism*
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Immunoglobulin lambda-Chains / analysis
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Immunoglobulin mu-Chains / analysis
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Macromolecular Substances
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Molecular Weight
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Palatine Tonsil / immunology
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Phosphorylation
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RNA / genetics
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RNA / isolation & purification
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RNA, Messenger / genetics
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RNA, Messenger / metabolism
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Receptors, Antigen, B-Cell / analysis
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Receptors, Antigen, B-Cell / metabolism*
Substances
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Antibodies, Monoclonal
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Immunoglobulin D
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Immunoglobulin G
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Immunoglobulin M
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Immunoglobulin lambda-Chains
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Immunoglobulin mu-Chains
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Macromolecular Substances
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RNA, Messenger
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Receptors, Antigen, B-Cell
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RNA