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, and B-cell malignancy.