B cell receptors (BCRs) are membrane-bound immunoglobulins expressed on the surface of B lymphocytes, playing a central role in adaptive immunity. Each BCR consists of an antigen-binding fragment formed by two heavy and two light chains, and a signaling component (Igα/Igβ heterodimer) that transmits signals upon antigen recognition. BCRs are highly diverse due to V(D)J recombination, enabling recognition of a vast array of pathogens.
When a BCR binds to a specific antigen, it triggers intracellular signaling cascades, leading to B cell activation, proliferation, and differentiation into antibody-secreting plasma cells or memory B cells. This process is tightly regulated: weak signals may induce tolerance, while strong signals drive immune responses. BCRs also facilitate antigen internalization and presentation to T cells, critical for initiating T cell-dependent antibody responses, including affinity maturation and class switching.
Dysregulation of BCR signaling is linked to diseases like autoimmune disorders (e.g., lupus) and B cell malignancies (e.g., chronic lymphocytic leukemia). Therapeutic strategies targeting BCR pathways, such as inhibitors of Bruton’s tyrosine kinase (BTK), have shown efficacy in treating certain cancers. Overall, BCRs are essential for pathogen detection, immune memory, and maintaining immune homeostasis.