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IMMUNOLOGICAL TOLERANCE, SANDHYA A 191822016 - Coggle Diagram
IMMUNOLOGICAL TOLERANCE
DEFINITION
Immune tolerance, or immunological tolerance, or immunotolerance, is a state of unresponsiveness of the immune system to substances or tissue that have the capacity to elicit an immune response in a given organism. It is induced by prior exposure to that specific antigen
MAJOR TYPES
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Induced tolerance.
deliberately manipulating the immune system to protect us from unpleasant, even dangerous, allergic reactions to such things as food
deliberately manipulating the immune system to enable transplanted organs (e.g., kidney, heart, liver) to survive in their new host; that is, to avoid graft rejection.
Preventing the immune system from mounting an inflammatory attack against the vast numbers of harmless (even beneficial) bacteria living in the intestine.
T-CELL TOLERANCE
Central Tolerance
T cells develop in the thymus. As they mature, recombination of gene segments creates the two chains that make up the T-cell receptor for antigen (TCR). Although the receptors on a single T cell are all alike, there is a virtually unlimited repertoire of receptor specificities created in the population of T cells within the thymus.
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T cells whose receptors bind these epitopes so tightly that they could attack the cell displaying them are deleted by apoptosis. The T cells that survive this negative selection leave the thymus and migrate throughout the immune system (lymph nodes, spleen, etc.).
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B-CELL TOLERANCE
The problem of B-cell tolerance is not so acute because B cells cannot respond to most antigens unless they receive help from T helper cells.
Central Tolerance
Any cells that produce a receptor for antigen (BCR) that would bind self components too tightly undergo a process of receptor editing. They dip again into their pool of gene segments that encode the light and heavy chains of their BCRand try to make a new BCR that is not a threat. If they fail, they commit suicide (apoptosis).
Peripheral Tolerance
B cells with a potential for attacking self can be kept in check by the absence of the T-helper cells they need; that is, T-cell tolerance is probably the most important (but not the only) mechanism for maintaining B-cell tolerance
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