biol 2160 final

biol 2160 final - Types of Specific Immune Responses...

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Types of Specific Immune Responses Humoral immunity (first line of defense before it gets into the cell) B cell mediated Involves secretion of antibodies by plasma cells (circulation in blood and lymph) Defend against bacteria, toxins, viruses in body fluids Cell-mediated immunity (once it gets into the cell) T cell mediated Involves lysis of cells by cytotoxic T cells (must come into direct contact with their targets in order to act on them) Defend against bacteria, viruses in body cells Part of reaction to transplants (except corniar transplants-no blood vessels here) and cancer cell both of which are perceived as foreign : respond to foreign or abnormal molecules known as antigens Both made in bone marrow T cells mature (become immunocompetant = recognize self from non-self) in thymus B cells mature in marrow Both recognize specific antigens through plasma membrane-bound antigen receptors (antigen-binding proteins) an enormous diversity of B and T cells, each bearing antigen receptors of particular specificity . Both have ability to develop memory of invaders T cells DO NOT RELEASE ANTIBODIES Specific Immune Response : highly selective (targets specific substances) and come into play after non-specific responses have already begun, mediated by lymphocytes (this is why they’re specific), strengthen with each exposure to a particular offending agent 1. Recognize Specific Invader foreign molecule that elicits a specific response by lymphocytes = antigen (Ag) Protein or carbohydrate (lipids do not cause a response, can go right through, small molecules) Large molecular size/complexity Dose & route of application are important. 2. Disable/Destroy Invader Humoral immunity using antibodies against extracellular invaders (disables) Depends on B lymphocytes Cell mediated immunity directly attacks intracellular invaders (destroys!) Depends on variety of T lymphocytes 3. Remember Invader Respond quickly to repeat assault Secondary response using Memory B Specificity Antigens (antibody generators) confer specificity Part of foreign invader, tumor cell Epitopes = recognition sites for B or T cells; none cell B cell and T cell specificity Antigen receptors recognize certain antigens only B cells – membrane antibodies, receptors bound to plasma membrane T cells – T cell receptors, act only as surface receptors for antigen, never secreted!! Antibody Structure : 2 heavy chains -2 light chains both joined by disulfide bridges; each antibody molecule is capable of binding to 2 epitopes of the same kind Constant region (c) – same within a class of antibodies, make up tail of antibody Variable region (v)– differs for different antigens, gives specificity to antigen-binding site, make up top of antibody 2 antigen-binding sites (2 identical variable regions) fig. 23.6a: typical antibody is y-shaped molecule consisting of 4 protein chains
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(a) each antibody molecule consists of 2 identical heavy chains and 2 identical light chains linked by disulfide bonds. The combind
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This note was uploaded on 06/25/2008 for the course BIOL 2160 taught by Professor Kt during the Spring '08 term at LSU.

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biol 2160 final - Types of Specific Immune Responses...

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