CD57, or Cluster of Differentiation 57, is a cell surface molecule used in immunology and diagnostics. This marker is a specific carbohydrate structure attached to proteins on the cell surface. It serves as an identifying tag for particular subsets of immune cells, allowing clinicians to monitor their populations in the bloodstream. Analyzing the count of cells that express CD57 is a standardized method, often performed using flow cytometry. This technique rapidly measures the characteristics of cells in a fluid stream, providing insights into the body’s immune status.
CD57 and Immune Cell Identification
The CD57 marker is primarily used to identify a specialized group of lymphocytes, a type of white blood cell. These include a distinct subset of Natural Killer (NK) cells and certain cytotoxic T-lymphocytes. NK cells are components of the innate immune system, defending against infected or abnormal cells. CD57 expression is a sign of terminal maturation in these NK cells, which are known for their potent cytolytic, or cell-killing, abilities.
CD57-positive NK cells are considered highly mature and possess a greater capacity to kill target cells compared to CD57-negative cells. On T-cells, particularly CD8+ T-lymphocytes, CD57 expression is associated with terminal differentiation and chronic antigen stimulation. These cytotoxic T-cells are specialized in immune surveillance, eliminating cells presenting foreign or abnormal antigens. The presence of CD57 indicates they are end-stage effectors that retain strong killing functions but are less capable of proliferation.
Chronic Infections and Low CD57 Counts
A low CD57 count, measured as the absolute number of CD57+ NK cells per microliter of blood, often correlates with chronic infections and immune exhaustion. While healthy individuals have a wide reference range, a count consistently below 60 to 100 cells/µL suggests immune dysregulation. This depletion is frequently observed in individuals suffering from Chronic Lyme Disease, caused by the bacterium Borrelia burgdorferi.
The persistent presence of Borrelia is believed to suppress the CD57+ NK cell population, leading to immune exhaustion. This reduction suggests an impaired ability to clear the infection, contributing to the prolonged symptoms of the chronic condition. Patients with chronic Lyme disease who experience neurological symptoms often exhibit lower CD57 levels than those with musculoskeletal symptoms. If treatment for the infection is successful, the CD57 count has been observed to return to the normal range, indicating its potential to track treatment response.
Low CD57 levels are also noted in conditions like Chronic Fatigue Syndrome (CFS/ME) and other persistent viral or bacterial infections. A persistent pathogen can drive immune cells into a state of functional impairment or depletion. In these chronic states, the body struggles to maintain a sufficient population of these mature killer cells, which contributes to ongoing chronic symptoms and fatigue.
CD57 as a Marker in Malignancy
CD57 expression is utilized as a diagnostic tool in classifying certain cancers through immunohistochemistry. This technique involves staining tissue samples to visualize the presence and location of the CD57 protein within a tumor mass. In the tumor microenvironment, the presence of CD57-positive cells, particularly NK cells, is often associated with a favorable prognosis in several solid tumors.
The accumulation of these cytotoxic cells suggests an active immune response attempting to destroy the malignant cells. For instance, a higher CD57 labeling index in the tumor stroma of oral squamous cell carcinoma is linked to better patient survival outcomes. Conversely, CD57 expression on CD8+ T-cells can be expanded in the peripheral blood of patients with various cancers, often correlating with the clinical stage of the disease.
High or localized CD57 expression is also a distinguishing feature in classifying specific hematologic malignancies and neuroectodermal tumors. CD57 is expressed on certain T-cell lymphomas and is a marker for identifying tumors of neural crest origin, such as peripheral nerve sheath tumors. In these diagnostic applications, the pattern of CD57 staining helps pathologists differentiate between abnormal cell growths, providing information about the tumor’s origin and biological behavior.
Understanding CD57 Test Results
CD57 testing is performed on a blood sample using flow cytometry, resulting in an absolute count of CD57-positive cells (cells/µL). Interpretation requires considering the laboratory’s established reference range, which can vary, but a normal count is generally above 60 to 130 cells/µL. Results are calculated by multiplying the percentage of CD57+ cells by the patient’s total lymphocyte count to ensure an accurate absolute number.
A count significantly below the reference range suggests depletion of the cytotoxic NK and T-cell subsets. This finding is often interpreted as chronic immune pressure, such as a persistent infection, where effector cells have been exhausted or suppressed. Conversely, an elevated CD57 count in the peripheral blood or tissue indicates strong, sustained immune activation. This increase occurs during acute immune responses or when the immune system attempts to eliminate cancer cells in the context of specific malignancies.
A CD57 count is only one piece of a larger clinical picture and is not a standalone diagnostic tool for any single disease. The numerical result must be interpreted by a healthcare provider alongside the patient’s medical history, physical examination findings, and other laboratory test results. Changes in the CD57 count over time, especially in response to treatment, provide more meaningful information than a single measurement.