The Immune system consists of white blood cells and a range of chemical substances, some of which circulate freely in the bloodstream, and others which are held in cellular stores, such as histamine in mast cells. In general terms neutrophils attack bacteria and viruses are attacked by lymphocytes. The lymphocytes also produce chemicals called gamma globulins that form antibodies, active in the attack on substances that are alien to us. The antibodies bind to the alien substance and thereby activate an inflammatory response, unleashing the chemicals which destroy the invader, and thereby keep us healthy. That's how it's supposed to be. Unfortunately sometimes the cells in the immune system become sensitised not to something that is alien, but to part of our own body tissues, and start to secrete antibodies to that particular tissue. This is the basis of the autoimmune disorders. Why it happens is unknown: there is certainly a genetic tendency since these disorders tend to run in families, but that cannot be the whole story since, for example, only one of a pair of identical twins might be affected by disease. Recovery from many disorders requires that we boost our immune system; the management of many of the disorders described in this section often means that we have to suppress it.
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