CD3 (immunology)

CD3 is a complex of proteins that is crucial in the immune system for the activation of T cells. It is part of the T cell receptor (TCR) complex, which is essential for the recognition of antigens presented by major histocompatibility complex (MHC) molecules on the surface of antigen-presenting cells (APCs).

Structure

The CD3 complex is composed of four distinct chains: CD3γ, CD3δ, and two CD3ε chains. These chains are associated with the TCR and the ζ-chain (zeta chain) to form the TCR-CD3 complex. The CD3 proteins are members of the immunoglobulin superfamily and contain immunoreceptor tyrosine-based activation motifs (ITAMs) in their cytoplasmic tails, which are critical for signal transduction.

Function

The primary function of the CD3 complex is to transduce signals from the TCR upon antigen recognition. When the TCR binds to an antigen-MHC complex, the ITAMs in the CD3 chains become phosphorylated by protein tyrosine kinases such as Lck and Fyn. This phosphorylation event initiates a cascade of intracellular signaling pathways that lead to T cell activation, proliferation, and differentiation.

Clinical Significance

CD3 is a target for various immunotherapeutic strategies. Monoclonal antibodies against CD3, such as OKT3, have been used in the treatment of acute transplant rejection and in certain autoimmune diseases. However, these treatments can be associated with significant side effects, including cytokine release syndrome.

Research Applications

CD3 is widely used as a marker in flow cytometry and immunohistochemistry to identify and quantify T cells. It is also a critical component in the study of T cell development and function in both basic and clinical research.

See Also

• T cell receptor
• Antigen-presenting cell
• Major histocompatibility complex
• Immunoglobulin superfamily
• Protein tyrosine kinase
• Monoclonal antibody

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