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kidneys. Some lymphocytes are also manufactured in the nodular glands of the lymphatic ducts, while some migrate from the bone marrow to the glands where they lie in wait, to be activated in an immune response. When a pathogen or toxin has gotten past the barrier of the skin or mucous membranes it moves into the connective tissue layer. If it is a pathogen, it starts to multiply and release toxins that are poisonous to the body tissues. It tries to get into the body stream to spread, but the body is already trying to isolate it in the connective tissue through phagocytosis (immune cells eating pathogenic cells). There are three main groups of phagocytes: (1) neutrophils, (2) mononuclear phagocytes (monocytes in the blood and macrophages in the connective tissue), and (3) organ-specific phagocytes (in the liver, spleen, lymph nodes, lungs, and brain). Some neutrophils and monocytes are stationed in the connective tissue, where they scavenge for invaders. If the invasion is big enough, they are joined by neutrophils and monocytes that squeeze out of the blood vessels and move into the connective tissue. Meanwhile, the monocytes release a chemical that signals the hypothalamus to set the thermostat of the body higher – to produce a fever. These nonspecific immune cells also release interferons, which interfere with viruses. The second, acquired, specific immune response follows up the first, if that is not sufficient to contain the invasion. This response is acquired and specific because it involves lymphocytes that have acquired, specific responses to the external genetic material they come in contact with. The body maintains a cellular library of foreign genetic configurations which it will attack when these enter the body. (This is how a vaccination works: it conveys knowledge of the foreign genotype to the body). The cells with the memory of the specific alien genetic program then are triggered to multiply. It takes a while for them to build up the millions of cells required to combat the invader, so this mechanism is slower than the innate, nonspecific method. However, it is required if that one does not do the job by itself. This secondary response involves the use of lymphocytes, of which there are two main kinds, Tcells and B-cells. The former are lymphocytes, manufactured in the bone marrow, but circulated

through the thymus, where they are trained to recognize external genetic configurations and not react against the host organism. This training is acquired in early childhood, after which the T-cells retain the memory of self and not-self, passing it on to future cell generations. They move to the site of the invasion destroy the intruder directly. The Bcells, on the other hand, are manufactured in the bone marrow but circulated throughout the fluids of the body. They secrete antibodies that interact with the antigens – the alien protein codes on the surfaces of the invading cells – to neutralize and destroy the invaders. Together, T- and B-cells provide immunity to viral, bacterial, fungal, and parasitic infections. Antibodies are proteins that are suited to the recognition of different proteins associated with different bacteria so they also represent a specific response. These proteins are also known as immunoglobulins. Some are suited to work in the more external secretions like saliva and milk, others are more internal. They grab onto the antigen, can rupture the wall of the invader cell, or anchor a complement protein which strangles the bacteria. Tcells do not use antibodies, but lymphokines, or interleukins for their coding purposes. The T-cells have additional functions as well as stopping external invasion. They are the “brains” of the immune system, carrying the codes for the recognition of self and not-self. Hence, they not only attack foreign bacteria, but also aberrant cells that arise within the body and would go on to produce cancer, or misplaced cells growing in the wrong places in the body. They are assisted by T-helper cells and controlled by T-suppresser cells. They are related to “natural killer cells” that nonspecifically destroy incipient cancer tumors. In areas of the body where there is special need for police-work the immune cells are incorporated into the linings to be at the sites where they are most needed. This kind of tissue is called “lymphoid.” It can be found in (1), the back of the throat and nasal passages – tonsils and adenoids – to protect the respiratory tract, (2), the small intestine to protect the body against alien genetic material and also to break that material down and absorb it for use as food, (3), at the end of the small intestine (Peyer’s Patches) to protect against septic material coming

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