B-cell receptor

The B-cell receptor 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. 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.

Components of the B-cell receptor
The B-cell receptor is composed of two parts :
 * 1) Ligand binding moiety: A membrane-bound bound immunoglobulin molecule of one isotype (IgD, IgM, IgE or IgE). With the exception of the presence of an integral membrane domain, these are identical to their secreted forms.
 * 2) 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).