What Is PBMC? Human PBMC Cells, PBMC Composition, and Isolation Tools

PBMC stands for peripheral blood mononuclear cell. PBMCs are a type of specialized immune cell that works together to keep our bodies safe from harmful pathogens.

Their presence in peripheral blood is significant because they serve as the first line of defense against infection and disease. Typically, PBMCs are isolated from whole blood samples using the best Cell Separation tools.

Where do PBMCs Come From?

PBMCs are derived from hematopoietic stem cells in the bone marrow (HSCs). HSCs serve as the foundation for all blood cells in the immune system. They develop two distinct lineages as they go through the process of hematopoiesis and differentiate into different cells. These lineages are myeloid and lymphoid. Certain myeloid and lymphoid cells, particularly those with a single round nucleus, are included in PBMCs.

HSCs help to strengthen the adaptive and innate immune systems as they develop into different lymphocytes, dendritic cells, and monocytes. The matured PBMC population will help the body defend against bacteria, viruses, and diseases by destroying foreign substances and tumor cells as they travel from the bone marrow to the peripheral bloodstream.

PBMC Cell Types

The three major cell types found in PBMC composition are as follows:

Lymphocytes
Monocytes
Dendritic Cells

Each of these cell types is in charge of performing a specific function.

Lymphocytes

Lymphocytes make up the vast majority of an enriched human PBMC sample, accounting for 70-90 percent of the total. Lymphocytes are the most abundant white blood cells (WBCs) because they come in a variety of types, each of which plays an important role in responding to diseases and infections. Lymphocytes are classified into the following groups in a human PBMC population:

The total number of CD3+ T cells – A sample’s lymphocytes will contain 45-70 percent naive, resting CD3+ T cells. These lymphocytes have not yet been activated by antigen recognition and are free to circulate throughout the body until they are required. Memory cells, which are already primed to combat a specific antigen and will reactivate upon exposure, could also be included among these cells. Memory T cells aid in the development of long-term immunity, whereas naive T cells develop the adaptive immune system to combat new harmful substances.

When CD3+ T cells are activated, they primarily develop into CD4+ or CD8+ T cells. Because their primary function is to activate an immune response, CD4+ T cells are referred to as helper T cells. They bind to antigen-presenting cells (APCs) with receptors and release chemicals to signal the location of invasive cells and mark them for elimination.

Helper T cells account for 25-60% of total activated CD3+ cells.

CD8+ killer T cells – A CD8+ killer T cell is the other differentiated T cell. These specialized lymphocytes, also known as cytotoxic T cells, are in charge of producing antibodies that seek out and destroy invasive cells. Approximately 5-30% of activated CD3+ cells develop into killer T cells.

B cells – Like T cells, the majority of B cells exist in the bloodstream as naive or memory cells. They differentiate into plasma cells after being activated by an antigen and can target freely circulating antigens. They can track down and destroy harmful cells that T cells cannot reach by secreting antibodies into extracellular space. B cells account for approximately 5-15 percent of total lymphocytes.

Natural killer (NK) cells – These are cells that attack and kill other people. Natural killer cells account for approximately 5-10% of lymphocytes. These cells are thought to be the human body’s natural front-line defense system. While T and B cells must be activated by antigens to perform their immune functions, NK cells do not require antigen activation. They are constantly on the move, defending the body from tumor activity.

Monocytes

Monocytes constitute a much smaller proportion of the human PBMC sample than lymphocytes — roughly 10-30%. These are the largest type of white blood cells and are found primarily in peripheral tissue. When stimulated, monocytes can differentiate into macrophages or dendritic cells. By removing unnecessary or dead cells, macrophages help shape the adaptive immune system.

Dendritic Cells

Dendritic cells are the third type of mononuclear immune cell. Dendritic cells are highly specialized APCs capable of completely engulfing an antigen before presenting a small portion of the same antigen to the immune system. T and B lymphocytes become activated and launch an attack against the cell population presented when the dendritic cell presents the APC fragment.

Isolation of Peripheral Blood Mononuclear Cells

The use of a density gradient centrifugationprocess is one of the techniques that aid in the separation of peripheral blood mononuclear cells from whole peripheral blood.

A density gradient centrifugation process separates the major cell populations, such as lymphocytes, monocytes, granulocytes, and red blood cells, across a density gradient medium because cells have a specific density. The medium will have a density of 1.077 g/ml for human cells to allow adequate separation of PBMCs (density 1.077 g/ml) from red blood cells and granulocytes (density > 1.077 g/ml).

Layering whole blood over a density medium without mixing the two layers, followed by centrifugation, will disperse the cells based on their densities. After centrifugation, the PBMC fraction will appear as a thin white layer at the plasma-density gradient medium interface, making it simple to remove.

PluriSelect offers optimized density gradient media for separating leukocytes, monocytes, platelets, and PBMCs from older blood. Our TwinSpin and pluriMate separation devices enable us to separate the target fraction regardless of the density of the impurities. The centrifugation tubes make handling easier and speed up the purification process.

Pluriselect developed a line of ready-to-use density gradient media for single-step density gradient centrifugation to isolate specific blood cell populations.

With a density of 1,077 g/ml at room temperature, PBMC-Spin can be used to isolate PBMC from fresh anti-coagulated blood.
To enrich all types of leukocytes from anti-coagulated blood, Leuko Spin works well. We recommend using it if you have to work with blood that is older than 12 or even 24 hours.
PBMC24+ Spin, which has been optimized for these conditions to reduce granulocyte contamination.
The density of Monocyte Spin Medium has been adjusted to separate the monocyte fraction with high efficiency.
PLT Spin Medium specifically removes the platelet fraction from blood cells.

PBMCs are an important component and a powerful tool in human health and disease research and clinical studies. With efficient Peripheral Blood Mononuclear Cell separation, researchers and clinicians can gain a better understanding of human diseases and apply their findings to treatments and cures.

Reference:

Science Direct

NCBI