CD Markers

The CD (Cluster of Differentiation) nomenclature was established in 1982 at the First International Workshop on Human Leukocyte Differentiation Antigens. It was intended for the classification of leukocytes according to the specific epitopes found at the cell surface, and at this inaugural meeting 139 monoclonal antibodies were evaluated.

CD45, also known as protein tyrosine phosphatase, receptor type, C (PTPRC), was originally known as common leukocyte antigen and is a signal transducer involved in many physiological processes such as growth and differentiation, cancer transformation, and the cell cycle. It is a transmembrane protein tyrosine phosphatase that regulates Src kinases in T- and B-cell receptor signal transduction (1).

Hematopoiesis is a complicated process that is controlled by both intrinsic and extrinsic cellular factors. It is a process of progression by which the diverse cell pedigrees that develop the blood and immune system are spawned from a shared pluripotent hematopoietic stem cell (HSC). Throughout the lifespan of an adult, two distinct hematopoietic systems are present, both resulting through embryonic development but only one of them enduring into adulthood.

Think B lymphocytes just produce antibodies? Think again! Although, of course, B cells are vital for the humoral immune response, many studies in recent years have begun to uncover antibody-independent actions of B cells: regulating T cells and thus also playing a part in cellular immunity. For example, B cell depletion therapy, a new treatment for autoimmune disorders, has been found to influence T cells in addition to antibody titers.

Cluster of differentiation (CD) antigens are membrane proteins in nature that are predominantly expressed on the leukocyte surface. However diminutive sums of CD antigens have also been reported to be expressed on other cell types which include the endothelial, stem, and dendritic cells along with erythrocytes.