Peripheral blood mononuclear cells, which are also called PBMCs or 
PB-MNCs, are blood cells that have round nuclei. They are critical to 
immune system functioning; they fight infection and foreign intruders in
 the body. Lymphocytes, monocytes and phagocytes are three examples of 
peripheral blood mononuclear cells.
Lymphocytes are white blood 
cells found in the immune system of vertebrates, animals with spinal 
columns and backbones. A scanning electron microscope (SEM) image can 
reveal a division between large and small lymphocytes.
Large 
lymphocytes are known as natural killer cells or NK cells. These PBMCs 
are the first line of defense against infection. Small lymphocytes 
include B cells and T cells, which play important roles in both antibody
 and non-antibody response.
Like lymphocytes, monocytes are white 
blood cells found in the vertebrate immune system. They are present in 
humans, mammals, birds, fish and reptiles. These peripheral blood 
mononuclear cells have multiple roles in immune system functioning. They
 produce and replenish various immune cells, and they respond to 
inflammation and infection signals.
Monocytes are produced in the 
bone marrow. Half of these monocytes are stored within the spleen. Those
 that migrate from the bloodstream to other tissues mature into 
different cell types, including macrophages.
Macrophages are 
essentially cells that monocytes produce in the tissues. Both 
macrophages and monocytes are phagocytes, another type of white blood 
cells. They offer immune protection through the ingestion of bacteria, 
dying cells and foreign particles.
Phagocytes are highly developed
 in vertebrates, especially humans. One liter of human blood contains 
nearly six billion of these phagocytes. Similarly to other white blood 
cells, they are highly critical for fighting infection, removing dead 
cells and maintaining healthy tissue.
Peripheral blood mononuclear
 cells have wide-ranging uses, from scientific research and clinical 
studies to cellular therapy. Healthy donors can give their blood cells 
for the testing of blood-borne pathogens. Donor cells are important to 
the study of HIV, Hepatitis B, syphilis and other infectious and 
auto-immune diseases. PBMCs are also used for vaccine development.
PBMCs
 are also vital to cellular therapy, a process that introduces new blood
 cells into damaged tissue to treat a particular disease. This type of 
therapy often focuses on hereditary diseases and may include gene 
therapy, stem cell treatments and cell replacement therapy.
