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WHAT ARE THE CELLS OF THE IMMUNE SYSTEM?

All white blood cells start in bone marrow as stem cells. The generic stem cells will divide and differentiate into all different types of white blood cells. Learning all of these different names and the function of each cell type takes a bit of effort but here's a quick summary to help get them organized in our brains:

All white blood cells are known officially as leukocytes. Leukocytes are divided into three classes:

  • Granulocytes - Granulocytes make up 50% to 60% of all leukocytes. Granulocytes are themselves divided into three classes: neutrophils, eosinophils and basophils.
  • Lymphocyte - Lymphocytes make up 30% to 40% of all leukocytes. Lymphocytes come in two classes: B cells (those that mature in bone marrow) and T cells (those that mature in the thymus).
  • Monocyte - Monocytes make up 7% or so of all leukocytes. Monocytes evolve into macrophages.

Each of the different types of white blood cells have a special role in the immune system and many are able to transform themselves in different ways:

  • Neutrophils are by far the most common form of white blood cells that you have in your body. Neutorphils are attracted to foreign material, inflammation and bacteria. Once a neutrophil finds a foreign particle or a bacteria it will engulf it, releasing enzymes, hydrogen peroxide and other chemicals from its granules to kill the bacteria.
  • Eosinophils and basophils are far less common than neutrophils. Eosinophils seem focused on parasites in the skin and the lungs, while Basophils carry histamine and therefore important (along with mast cells) to causing inflammation. From the immune system's standpoint inflammation is a good thing. It brings in more blood and it dilates capillary walls so that more immune system cells can get to the site of infection.
  • Of all blood cells, macrophages are the biggest. Monocytes are released by the bone marrow, float in the bloodstream, enter tissue and turn into macrophages.
  • The lymphocytes handle most of the bacterial and viral infections that we get. Those destined to become B cells develop in the marrow before entering the bloodstream. T cells start in the marrow but migrate through the bloodstream to the thymus and mature there.
  • B cells, when stimulated, mature into plasma cells -- these are the cells that produce antibodies. A specific B cell is tuned to a specific germ, and when the germ is present in the body the B cell clones itself and produces millions of antibodies designed to eliminate the germ.
  • T cells, on the other hand, actually bump up against cells and kill them. T cells known as Killer T cells can detect cells in your body that are harboring viruses, and when it detects such a cell it kills it.
  • Dendritic Cells are usually found in the structural compartment of the lymphoid organs such as the thymus, lymph nodes and spleen. It is believed that they capture antigen and bring it to the lymphoid organs where an immune response is initiated. Read more...What are the organs of the immune system