A CD138 plasma cell is a specialized immune cell that carries a unique protein marker, CD138, on its surface. Medical professionals use this marker to identify these cells during various diagnostic tests. Understanding this marker helps in recognizing certain conditions within the body, guiding both diagnosis and patient management.
The Role of Normal Plasma Cells
Plasma cells are a type of white blood cell that develops from B lymphocytes. When B cells encounter foreign invaders, such as bacteria or viruses, and receive activating signals, they transform into these specialized cells. Their primary purpose is to produce and secrete large quantities of proteins called antibodies.
These antibodies act as specialized defenders, recognizing and neutralizing harmful substances, called antigens, that circulate in the bloodstream and lymphatic system. Plasma cells are efficient antibody factories, providing the body with a robust defense against infection.
Plasma cells can be categorized into short-lived and long-lived populations. Short-lived plasma cells emerge rapidly in lymphoid organs like the spleen following initial antigen exposure, contributing to the immediate immune response. Long-lived plasma cells migrate primarily to specialized niches within the bone marrow, where they can persist for years or even a lifetime. These enduring cells continue to produce antibodies, offering sustained protection and forming the basis of lasting immunity.
Understanding the CD138 Marker
The identifier “CD” in CD138 stands for “Cluster of Differentiation,” a standardized naming system for proteins found on the surface of cells. CD138 is scientifically known as Syndecan-1, and it belongs to a family of transmembrane proteoglycans. Syndecan-1 is involved in mediating cell-cell adhesion and cell-matrix adhesion. Because CD138 is expressed at high levels on the surface of mature plasma cells, it serves as a reliable marker for their identification. While CD138 can also be detected on certain other cell types, its abundant and specific expression on plasma cells makes it an accurate tool for pathologists examining hematopoietic tissues.
Clinical Significance in Diagnosis
Medical professionals frequently test for CD138-positive plasma cells because their presence and quantity can provide important diagnostic information. A primary application is in diagnosing multiple myeloma, a cancer characterized by the uncontrolled proliferation of abnormal plasma cells in the bone marrow. In a healthy individual, plasma cells typically constitute 2% to 3% of bone marrow cells. In multiple myeloma, abnormal plasma cells make up at least 10% of the cells in the bone marrow, often crowding out other healthy blood cell types. These malignant plasma cells produce an excess of abnormal antibodies, known as paraproteins, which can be detected in blood or urine and contribute to disease symptoms such as bone lesions, kidney problems, and anemia. Identifying CD138-positive cells helps confirm the diagnosis of multiple myeloma and assess the disease burden.
Beyond cancer, CD138 plasma cells are also significant in diagnosing chronic endometritis, an inflammatory condition affecting the lining of the uterus. The presence of any plasma cells in the endometrial stroma is considered abnormal and indicative of inflammation, as they are typically absent in a healthy endometrium. Traditional methods for diagnosis can be challenging due to the varied morphology of endometrial cells, but immunohistochemistry using CD138 antibodies greatly improves the accuracy and sensitivity of detecting these plasma cells in tissue samples.
Studies suggest that chronic endometritis, particularly when characterized by the presence of five or more CD138-positive plasma cells per high-power microscopic field, is associated with adverse reproductive outcomes, including lower live birth rates and higher pregnancy loss rates in patients undergoing in vitro fertilization. The prevalence of chronic endometritis in women of reproductive age can vary widely, with reported incidences ranging from approximately 8% to 72%.
Methods of Detection
Laboratories employ specific techniques to identify and quantify CD138 plasma cells. One common method is immunohistochemistry (IHC), which is performed on fixed tissue samples. In this technique, a thin slice of the tissue is treated with highly specific antibodies that are designed to bind precisely to the CD138 protein on the surface of plasma cells. These specialized antibodies are often conjugated with an enzyme or fluorescent tag, making the CD138-positive plasma cells readily identifiable under a microscope. Immunohistochemistry using CD138 antibodies offers increased sensitivity for detecting plasma cells in tissue compared to conventional hematoxylin and eosin (H&E) staining.
Another widely utilized method is flow cytometry, which analyzes cells suspended in a liquid sample, such as bone marrow aspirates or peripheral blood. In this process, cells are first labeled with fluorescently tagged antibodies specific to CD138 and then passed individually through a focused laser beam. As each cell passes, the laser excites the fluorescent markers, and detectors measure the emitted light signals, as well as light scattering properties that provide information about cell size and granularity. This high-throughput technique allows for the rapid and precise identification, enumeration, and characterization of CD138-positive plasma cells within a mixed cell population. It is also frequently employed to assess the purity of CD138-positive cell populations after they have been isolated for further genetic or molecular analysis.