CD antigens are proteins found on cell surfaces, acting as unique identifiers. Abundant on immune cells, they enable scientists to distinguish cell types and developmental stages. This system is fundamental to understanding normal biological processes and disease states.
Understanding CD Antigens
CD antigens, short for “Cluster of Differentiation,” are surface proteins. This naming system was established in 1982 at the first Human Leukocyte Differentiation Antigen (HLDA) Workshop in Paris to categorize monoclonal antibodies developed against leukocyte surface molecules. Over time, this system expanded beyond white blood cells; currently, over 370 unique CD clusters and subclusters have been identified.
Each CD antigen is assigned a specific number, like CD3 or CD4. For instance, CD3 is a protein complex on T cells, while CD4 and CD8 are on helper T cells and cytotoxic T cells, respectively. When referring to cell populations, a plus (+) or minus (-) symbol indicates the presence or absence of a CD molecule; for example, “CD34+, CD31-” denotes a cell expressing CD34 but lacking CD31.
Functions of CD Antigens
CD antigens play diverse biological roles as receptors, ligands, and adhesion molecules that facilitate cellular interactions. These surface molecules enable cells to recognize each other, important for immune cells to differentiate between healthy and infected cells. They also help coordinate immune responses by initiating signal cascades within cells.
Many CD antigens are involved in signal transduction, enabling cells to respond to their environment. For example, CD4 and CD8 on T cells interact with Major Histocompatibility Complex (MHC) molecules, activating T cells for an immune response. Other CD antigens mediate cell adhesion, allowing cells to form contacts, important for tissue formation and maintenance. Some CD antigens, like CD27, CD30, and CD40, also function as cytokine receptors, influencing cytokine activity.
CD Antigens in Health and Disease
CD antigens are utilized in medicine and research to identify and characterize cell populations. In diagnostics, they are valuable for classifying blood cancers like leukemia and lymphoma, identified by unique CD marker profiles. For instance, CD19 and CD20 markers are used to diagnose and subtype B cell lymphomas, while CD3 is important for diagnosing T cell leukemias.
Beyond diagnosis, CD antigens monitor the immune system, offering insights into disease progression and treatment. For instance, in HIV/AIDS patients, CD4+ T cell counts are tracked to assess disease progression and antiretroviral therapy effectiveness. Changes in CD marker expression also indicate tumor growth or regression, helping monitor treatment effects. Furthermore, CD markers are targets for new therapies, including monoclonal antibody and CAR T-cell therapies, targeting specific CD antigens on cancer cells.