BCr

BCR stands for B cell receptor, a membrane-bound receptor complex that enables B lymphocytes to recognize specific antigens. In humans and other jawed vertebrates, the BCR is composed of a membrane-bound immunoglobulin molecule that provides antigen specificity, associated non-covalently with signaling chains CD79A (Igα) and CD79B (Igβ). The immunoglobulin portion determines which antigen is recognized, while CD79A and CD79B contain ITAM motifs that initiate signaling upon antigen binding.

When an antigen binds the BCR and causes receptor cross-linking, Src-family kinases such as Lyn phosphorylate the ITAMs, creating docking sites for the Syk kinase. This triggers downstream signaling through adapters such as BLNK and pathways including PLCγ2, calcium flux, MAP kinases, and NF-κB. The resulting signals lead to B cell activation, proliferation, and differentiation into antibody-secreting plasma cells or memory B cells. BCR signaling also promotes antigen internalization for processing and presentation on MHC class II molecules, facilitating interactions with helper T cells.

BCR diversity is generated during B cell development by V(D)J recombination of the immunoglobulin genes. In germinal centers, somatic hypermutation and class switch recombination—driven by activation-induced cytidine deaminase (AID) and T cell help—refine antigen affinity and effector function. Proper BCR signaling is essential for immune tolerance, while dysregulation can contribute to autoimmunity or B cell malignancies.