B cell receptor and T cell receptor of the adaptive immune system (BCR and TCR)

The B cell receptor (BCR) and T cell receptor (TCR) are highly specialized, membrane-bound protein complexes expressed respectively on B lymphocytes and T lymphocytes, enabling antigen-specific recognition during adaptive immune responses. - BCR is a membrane-bound immunoglobulin composed of two identical heavy chains and two light chains (either kappa or lambda isotypes) forming two antigen-binding sites, coupled to signaling heterodimers Igα and Igβ (CD79a/CD79b) that initiate intracellular signaling cascades upon antigen binding. - TCR consists of either an alpha and beta chain (most common) or gamma and delta chains (less common), each with variable and constant regions; antigen recognition is limited to peptides presented by MHC molecules. TCR is associated with a complex of CD3 proteins, each containing immunoreceptor tyrosine activation motifs (ITAMs) that trigger downstream signaling on antigen engagement. Both receptor complexes are central to the activation, differentiation, and effector functions of lymphocytes, underpinning the generation of immunological memory, specificity, and self/non-self discrimination that define the adaptive immune system. Therapeutic modulation of BCR and TCR and their signaling pathways plays a major role in immuno-oncology, autoimmunity, and inflammatory disease interventions.

Other names

BCR (B cell receptor)TCR (T cell receptor)Membrane immunoglobulin (for BCR)Antigen receptor

Signal inhibition (e.g., targeting kinases in BCR or TCR pathway, such as BTK, Syk or Src family kinases); Cell depletion (antibody-dependent cellular cytotoxicity, as with anti-CD20 antibodies for B cells); Immunomodulation (agonists or antagonists affecting immune activation, e.g., blocking co-receptors); Induction of apoptosis (in targeted cell types).