Peripheral Blood Mononuclear Cells, often referred to as PBMCs, are a specific type of immune cell found circulating in the blood. These cells are characterized by having a single, round nucleus, distinguishing them from other blood components. PBMCs represent a collection of the body’s defense cells, playing a significant role in immune responses. Understanding these cells provides insight into how the body combats infections and diseases.
Cellular Composition of PBMCs
PBMCs are primarily composed of two main categories of white blood cells: lymphocytes and monocytes. Lymphocytes constitute the majority of the PBMC population, ranging from 70% to 90%. These include T cells, B cells, and Natural Killer (NK) cells, each performing distinct immune functions. T cells are involved in directly attacking infected or cancerous cells, while B cells are responsible for producing antibodies that neutralize pathogens. NK cells contribute to the body’s defense by recognizing and destroying compromised cells, such as those infected with viruses or tumor cells.
Monocytes make up a smaller portion of the PBMC sample, between 10% and 20%. These cells are the largest type of white blood cells and can differentiate into macrophages or dendritic cells when stimulated. Macrophages are involved in clearing cellular debris and presenting antigens, while dendritic cells are powerful antigen-presenting cells that activate T cells.
During isolation, red blood cells, which lack a nucleus, are removed. Granulocytes, such as neutrophils, eosinophils, and basophils, are also excluded from the PBMC fraction because they possess multi-lobed nuclei and have a different density. This selective removal ensures that researchers obtain a purified sample of immune cells with specific characteristics for study.
Isolation from Whole Blood
Scientists routinely isolate PBMCs from whole blood samples to study them in a controlled environment. The most common method for obtaining a pure sample involves a technique called density gradient centrifugation. This process separates blood components based on their differing densities, much like how oil and water separate into layers. Whole blood is carefully layered over a specialized medium, Ficoll-Paque, which has a specific density of around 1.077 grams per milliliter.
When this layered mixture is centrifuged, the various blood components settle into distinct layers according to their weight. Red blood cells and granulocytes, being denser, pass through the Ficoll-Paque medium and collect at the bottom of the tube. PBMCs, having a density lower than the Ficoll-Paque but higher than the plasma, form a distinct white layer known as the “buffy coat” at the interface between the plasma and the separation medium. This allows researchers to carefully collect this enriched layer for further analysis.
Role in Scientific Research and Medicine
PBMCs are widely used in scientific research and medicine due to their accessibility and their reflection of the body’s immune status. In immunology, these cells are important for investigating the immune system’s response to infections, vaccines, and autoimmune disorders. Researchers can stimulate PBMCs in the laboratory to observe how they react to specific pathogens or antigens, providing insights into immune memory and activation pathways. This helps in understanding disease progression and developing new preventive strategies.
In cancer research, PBMCs offer a window into the systemic immune response against tumors. They are used to study the effectiveness of immunotherapies, which harness the body’s own immune system to fight cancer. Analyzing PBMC populations can help identify biomarkers that predict how a patient might respond to certain cancer treatments.
PBMCs also play a role in monitoring the progression of infectious diseases, such as HIV. By analyzing specific T cell populations within PBMCs, scientists can track the course of the infection and the patient’s immune health. The ease of obtaining PBMCs from routine blood draws makes them a practical sample for diagnostic and prognostic biomarker identification across a range of conditions, including chronic obstructive pulmonary disease, heart disease, and rheumatoid arthritis.