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| B-cell receptor ： ウィキペディア英語版 |
B-cell receptor
The B-cell receptor or BCR is a transmembrane receptor protein located on the outer surface of B-cells. The receptor's binding moiety is composed of a membrane-bound antibody that, like all antibodies, has a unique and randomly determined antigen-binding site (see V(D)J recombination). When a B-cell is activated by its first encounter with an antigen that binds to its receptor (its "cognate antigen"), the cell proliferates and differentiates to generate a population of antibody-secreting plasma B cells and memory B cells. The B cell receptor (BCR) has two crucial functions upon interaction with the antigen. One function is signal transduction, involving changes in receptor oligomerization. The second function is to mediate internalization for subsequent processing of the antigen and presentation of peptides to helper T cells. BCR functions are required for normal antibody production, and defects in BCR signal transduction may lead to immunodeficency, auto-immunity and B-cell malignancy.
== Components of the B-cell receptor ==
The B-cell receptor is composed of two parts:
i) A membrane-bound immunoglobulin molecule of one isotype (IgD, IgM, IgA or IgE). With the exception of the presence of an integral membrane domain, these are identical to their secreted forms.
ii) Signal transduction moiety: A heterodimer called Ig-α/Ig-β (CD79), bound together by disulfide bridges. Each member of the dimer spans the plasma membrane and has a cytoplasmic tail bearing an ''immunoreceptor tyrosine-based activation motif (ITAM).''
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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