| Term 
 | Definition 
 
        | When tissue is transplanted from one part of your body to another |  | 
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        | Term 
 | Definition 
 
        | Tissue transplant between members of the same species (i.e. human to human)Tissue will be rejected if donor and receiver tissue do not match |  | 
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        | Term 
 | Definition 
 
        | Tissue transplant between members of different species (i.e animal to human) always unsuccessful |  | 
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        | Term 
 | Definition 
 
        | Preformed antibodies are already present and therefore the tissue dies immediately |  | 
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        | Term 
 | Definition 
 
        | Receipient recognize tissue as forein and begins to form antibodies against it |  | 
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        | Term 
 | Definition 
 
        | Many alternatice copies of a gene are in circulation, as a result virus cant use MHC molecules as a receptor |  | 
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        | Term 
 
        | B-Cell Positive Selection |  | Definition 
 
        | The cell must be able to produce an antibody which can bind to antigen in order to continue. |  | 
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        | Term 
 
        | B-Cell Negative Selection |  | Definition 
 
        | The antibody will be killed if it recognizes self antigen, those that do not recognize self will be allowed to continue. |  | 
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        | Term 
 | Definition 
 
        | Primary immune tissue where T-Cells mature |  | 
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        | Term 
 | Definition 
 
        | Site of production of B and T Cells |  | 
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        | Term 
 | Definition 
 
        | Recognizes Class II molecules which are helper T Cells |  | 
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        | Term 
 | Definition 
 
        | Helper cells which secrete cytokine and interferon gamma which tell B cells to produce specific antibodies and to upregulate the immune response (IL-12) |  | 
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        | Term 
 | Definition 
 
        | Helper T cells which secrete cytokines and IL-4 which upregulates B cell response (humoral immunity) (IgG1 and IgE) |  | 
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        | Term 
 | Definition 
 
        | Recognizes Class I molecules |  | 
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        | Term 
 
        | T-Cell Positive Selection |  | Definition 
 
        | T-cells which recognize self antigen are allowed to continue |  | 
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        | Term 
 
        | T-Cell negative selection |  | Definition 
 
        | T-cells which recognize self with a strong affinity are killed and those who have a low affinity for self continue |  | 
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