Mouse Anti-Human CD3 Antibody (S-5506)

CD3 is a key signaling component of the T cell receptor (TCR) complex, composed of multiple transmembrane polypeptide chains that bind non-covalently to the αβ or γδ heterodimers of the TCR, together forming the TCR/CD3 complex. This complex comprises the CD3γ, δ, ε, and ζ chains, among which CD3γ/δ/ε each contain an extracellular immunoglobulin-like domain and an immunoreceptor tyrosine-based activation motif (ITAM), while CD3ζ possesses a short extracellular domain and three ITAMs. The TCR itself lacks a significant intracellular signaling domain, so antigen recognition signals must be transmitted intracellularly through ITAM phosphorylation of the CD3 subunits, which subsequently recruit adaptor proteins such as Nck, initiating T cell activation, proliferation, and survival signals. The CD3ζ chain plays a critical role in the signaling cascade, triggering various biochemical events and second messenger activation, leading to transcription factor expression and enhanced effector functions. The assembly of the CD3 complex is strictly regulated by conserved charged residues in the transmembrane regions; the loss of any subunit causes the TCR to be retained in the endoplasmic reticulum or targeted for lysosomal degradation, while mutations in the CD3D, CD3E, CD3G, or CD3Z genes can cause T cell immunodeficiencies such as severe combined immunodeficiency. Because CD3 expression is strictly restricted to T lymphocytes, anti-CD3 antibodies have become highly specific markers for identifying T cells and hold important value in the diagnosis of T cell lymphomas.