CD is short for cluster of differentiation. Cluster of differentiation is cell surface marker that appears or disappears in the normal differentiation and maturation of white blood cells (including platelets, vascular endothelial cells, etc.) at different lineage (lineage), different stages and the activation process. They are mostly transmembrane proteins or glycoproteins, including extracellular, transmembrane and cytoplasmic regions. Some clusters of differentiation are “anchored” to the cell membrane by inositol phospholipids (IP) connection. A few clusters of differentiation are carbohydrate haptens.
I believe that in the previous series, you have got a certain understanding of the function of leukocyte differentiation antigen. In many cases, antibodies and the antigens they recognize use the same CD number. So, let’s start with the following typical CD molecules:
1. CD46
CD46, is also known as membrane cofactor protein (MCP), is type I transmembrane glycoprotein expressed in all nucleated cell. The main function of CD46 is as a cofactor, promote protease factor Ⅰ mediated C3b and C4b degradation, and enhance the C3 invertase activity, is considered to be the complement bypass activation pathways of the most effective inhibitory factor. Therefore, CD46 regulates the function of complement by inhibiting the cascade reaction activated by C3 molecule, and protects the host’s own normal cells from the complement mediated lysis. In addition, CD46 is also a receptor for many viruses, bacteria and other pathogens, and can trigger certain biological or immunological effects by specific binding to these pathogens through the extracellular domain.
2. CD70
CD70, a member of the tumor necrosis factor receptor (TNFR) family, has the ability to regulate the activation, proliferation and differentiation of T cells and B cells, and plays an important role in maintaining the immune response of the body. Meanwhile, CD70 is highly expressed in various tumor tissues, which may be an effective target molecule for tumor immunotherapy.
Structure and function: a member of the tumor necrosis factor receptor family, a ligand of CD27.The interaction between CD70 and its ligands is an important part of early function after antigen stimulation.
Normal expression: about 10% of peripheral blood B cells, about 10% of germinal center B cells; It is expressed on activated B and T cells.
Abnormal expression: neoplastic B cells, such as partial follicular lymphoma, partial large B cell lymphoma, and partial chronic lymphocytic leukemia; Riess cells; Nasopharyngeal carcinoma and some thymic tumors.
When expressed on malignant cells, it is often co-expressed with the ligand CD27, which acts as a receptor to facilitate tumor cell proliferation.
3. CD74
CD74 is a kind of non-polymorphism Ⅱ transmembrane glycoprotein, expressed on B cells, but not expressed in B cell precursors; It can also be expressed in activated T cells, monocytes, macrophages, activated endothelial cells and activated epithelial cells. In 2003, it was found that, as a high-affinity membrane receptor of macrophage mobile inhibitory factor (MIF), it is involved in a variety of MIF-mediated signaling pathways, and is closely related to the development of inflammatory diseases, autoimmune diseases, metabolic diseases and tumor diseases.
4. CD97
CD97 is one of family members of the epidermal growth factor-seven transmembrane (EGF-TM7). Of the dozens of reports on CD97 molecule in tumor research so far, the in vivo and in vitro studies on thyroid cancer as well as colon cancer are the most systematic and convincing, the common conclusion is: 1. CD97 molecule was highly expressed in both tumor tissues and in vitro cultured tumor cells; 2. The expression intensity of CD97 in colon cancer cell lines was correlated with the migration and invasion ability of the cell lines; 3. The expression pattern of CD97 molecule is transient and dynamic in tumor tissue, that is, individual tumor cells or tumor cell clusters scattered along the infiltration edge of tumor tissue have CD97 strong positive staining; 4. The positive expression of CD97 molecule is related to the differentiation, invasion, metastasis and clinical staging of malignant tumors, and is an important target molecule for tumor treatment and prognosis. However, there has been no systematic study on the expression of CD97 molecule in tissues and cells of other tumors (including gastric cancer).
5. CD180
CD180, originally known as RP105, is a TLR homologous that is involved in TLR-4 recognition of bacterial LPS and is therefore involved not only in dendritic cells but also in innate immunity of B cells.
Cluster of differentiation is involved in important physiological and pathological processes. The research on it is of great significance to the advancement of biological science. We will also introduce more members of the CD family in the future.