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White blood cells (also called leukocytes or immune cells) are a component of blood. They help to defend the body against infectious disease and foreign materials as part of the immune system. There are normally between 4x109 and 11x109 white blood cells in a litre of healthy adult blood.As well as in the blood, white cells are also found in large numbers in the lymphatic system, the spleen, and in other body tissues.
1 Types
There are three major types of white blood cells.
1.1 Granulocytes
Granulocytes are a category of white blood cells, characterised by the fact that all types have differently staining granules in their cytoplasm on light microscopy. There are three types of granulocytes: neutrophils, basophils and eosinophils (named according to their staining properties).
1.2 Lymphocytes
Lymphocytes are much more common in the lymphatic system, and include the so-called " killer T-cells". The blood has three types of lymphocytes: B cells, T cells and natural killer cells. B cells make antibodiesantigen An antibody is a protein complex used by the immune system to identify and neutralize foreign objects like bacteria and viruses. Each antibody recognizes a specific antigen unique to its target. Antibody structure Antibodies are glycoproteins foun that bind to pathogens to enable their destruction. CD4+ ( helperA helper (or T T cell is a T cell (a type of white blood cell) which has on its surface antigen receptors that can bind to fragments of antigens displayed by the Class II MHC molecules found on professional antigen-presenting cells (APCs). Once bound to a) T cells co-ordinate the immune response (they are what become defective in an HIVThe Human immunodeficiency virus HIV is a frequently mutating retrovirus that attacks the human immune system and which has been shown to cause acquired immune deficiency syndrome (AIDS). History HIV was discovered and identified as the agent for AIDS by infection). CD8+ ( cytotoxicA cytotoxic (or T T cell is a T cell (a type of white blood cell) which has on its surface antigen receptors that can bind to fragments of antigens displayed by the Class I MHC molecules of virus infected somatic cells and tumor cells. Once activated by a) T cells and natural killer cells are able to kill cells of the body that are infected by a virus.
1.3 Monocytes
MonocyteA monocyte is a white blood cell, part of the human body's immune system. It is one of the 5 major types of white blood cell, based on the appearance of white blood cells, in stained smears, as viewed under a light microscope. Monocytes evolve from the bos share the 'vacuum cleaner' function of neutrophils, but are much longer lived as they have an additional role. Monocytes, and their tissue counterpart macrophages, present pieces of pathogenA pathogen is a biological agent that can cause disease to its host. A synonym of pathogen is " infectious agent". The term "pathogen" is most often used for agents that disrupt the normal physiology of a multicellular animal or plant. However, pathogenss to T cells so that they may be recognised again and killed, or so that an antibody response may be mounted.
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