CD45 is a protein found on the surface of many cells, serving as a marker to distinguish cell types and provide insights into cellular identity and function.
What is CD45?
CD45 is a large transmembrane glycoprotein, also known as Leukocyte Common Antigen (LCA) due to its widespread presence on white blood cells. The “CD” in CD45 stands for “Cluster of Differentiation,” a standardized nomenclature system used to classify and identify cell surface molecules.
This protein functions as a protein tyrosine phosphatase, an enzyme that plays a significant role in cellular signaling. CD45 is involved in regulating the activation of immune cells and their development. By removing phosphate groups from specific protein targets, CD45 can influence various cellular pathways critical for immune responses.
CD45’s Role in Identifying Immune Cells
CD45 is almost universally expressed on cells that originate from the hematopoietic stem cells in the bone marrow. This includes all types of white blood cells, such as lymphocytes, monocytes, and granulocytes. Because of its pervasive presence on these cells, CD45 is recognized as a “pan-leukocyte marker,” which means it can be used to identify virtually all white blood cells in a sample.
This widespread expression distinguishes immune cells from other cell types. Non-hematopoietic cells, such as epithelial cells, fibroblasts, or mature red blood cells, typically do not express CD45. This allows researchers and clinicians to isolate and analyze immune cell populations, as CD45 indicates a cell’s immune system lineage.
CD45’s Clinical Significance in Disease
The unique expression pattern of CD45 is leveraged in clinical diagnostics, particularly through a technique called flow cytometry. This method uses fluorescently labeled antibodies that bind to specific cell surface markers, including CD45, allowing for the identification and quantification of different cell populations. By measuring CD45 expression, clinicians can count the various types of white blood cells in a patient’s blood or bone marrow sample.
CD45 expression is important in diagnosing blood cancers such as leukemia and lymphoma. Different types of leukemia, like acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL), often exhibit distinct patterns of CD45 expression. For instance, some malignant cells in AML might show dimmer or lower levels of CD45 expression compared to normal white blood cells, while certain ALL subtypes might have absent or very low CD45. These abnormal expression patterns serve as diagnostic indicators.
Analyzing CD45 expression helps in differentiating various cell lineages, which aids in classifying unknown cells in a patient sample. Monitoring changes in CD45 expression levels or patterns over time can also provide insights into disease progression and a patient’s response to treatment. This allows for tailored therapeutic strategies based on the specific characteristics of the malignant cells.