CD3 Homodimers & Heterodimers

Background

Cluster of Differentiation 3 (CD3) is a multimeric protein complex and T cell co-receptor that plays an essential role in adaptive immune responses. This complex is composed of four distinct polypeptide chains: epsilon (ε), gamma (γ), delta (δ), and zeta (ζ), which assemble as three pairs of dimers (εγ, εδ, ζζ). These CD3 molecules bind non-covalently to the T-cell receptor (TCR) to form the TCR/CD3 receptor complex on the surface of T cells.

CD3 proteins interactions with T cells

The CD3 proteins have a transmembrane domain, a cytoplasmic tail, and an N-terminal extracellular region containing immunoglobulin-like domains, classifying them as part of the immunoglobulin superfamily. The intracellular immunoreceptor tyrosine-based activation motifs (ITAMs) located in the cytoplasmic tails are essential for signal transduction upon T cell receptor engagement.

The CD3 complex is a defining feature of the T cell lineage and is involved in activating both cytotoxic T cells (CD8+ naive T cells) and T helper cells (CD4+ naive T cells). Antibodies against CD3 molecules can either stimulate or block T cell activation signal transduction, offering a potential avenue for developing treatments for organ transplant rejection and autoimmune diseases.