CD3 (Cluster of differentiation 3), originally known as T3, is one of the first groups of human T lymphocyte surface antigens recognized by monoclonal antibodies. It has been reported that antibodies against CD3 could either stimulate T cells to divide or inhibit the progress of effector functions according to the conditions used. It plays an important role in T cell and the CD3 T-cell co-receptor helps to activate the cytotoxic T-Cell and T helper cells. The CD3 molecule is composed of a protein complex and consists of four distinct chains. The complex of mammals contains a CD3γ chain, a CD3δ chain, and two CD3ε chains. All these chains associate with T-cell receptor and the ζ-chain to generate an activation signal in T lymphocytes.
CD123 (Cluster of differentiation 123), also known as IL-3R or IL-3RA (Interleukin-3 (IL-3) receptor α-chain), is a membrane receptor belonging to the type I cytokine receptor family. This glycoprotein of 360 amino acids includes a predicted Ig-like domain, a transmembrane domain, an intracellular domain and two FnIII domains and can help transmit the signal of IL-3. The protein encoded by CD123 is an IL-3 specific subunit of a heterodimer composed of α- and β-chains. It is thought to be involved in cell signal transduction for the cell growth and differentiation. CD123 is normally expressed on monocytes, basophils, endothelial cells, and plasmacytoid dendritic cells. It is associated with the development of many diseases and considered as a novel marker in the clinical diagnosis.
CD33 (Cluster of differentiation 33), also known as p67 or SIGLEC-3 (Sialic acid binding Ig-like lectin 3), is a type I transmembrane glycoprotein of 67kDa. It is a sialoadhesin molecule belonging to the immunoglobulin supergene family and SIGLEC family of lectins. CD33 is a myeloid cell surface antigen that is specific for the myeloid lineage, but it also can be found on certain lymphoid cells as a restricted leukocyte antigen. It is expressed on myeloid stem cells, myeloblasts, monoblasts, monocytes/macrophages, granulocyte precursors, and mast cells. CD33 is a remarkable myeloid marker and is commonly applied in the diagnosis of acute myeloid leukemia (AML). And 10% to 20% of B lymphoblastic or T lymphoblastic leukemia/lymphomas are likely to aberrantly express CD33.