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Published byBridget Berry Modified over 8 years ago
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Chapter 43 43.2-43.3 Pgs. 935-946 Objective: I can describe how adaptive immunity (immunological memory) works. Challenging but cool, like a Rube Goldberg device (complex mechanism)
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Lymphocytes involved (type of leukocyte) 2 types: B cells and T cells 2 sub-types of T cells…(more later) Cytokines: proteins that activate lymphocytes; secreted by phagocytes Antigen: any foreign molecule recognized by lymphocytes (protein, polysaccharide, etc.) Some extend from cell surface Others dissolved in extracellular fluid All have epitopes: portions of antigen that lymphocyte specifically binds to
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All blood cells start in bone marrow (pluripotent stem cells) B cells develop in Bone marrow T cells develop in Thymus Each individual lymphocyte (B or T cell) has ~100,000 antigen receptors on its cell surface bind to antigen But, ALL receptors identical!!! (for a given cell) Thus, have millions of different B/T cells
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B Cell Receptor (BCR) is Y-shaped (2 antigens) Made of 2 heavy chains & 2 light chains Chains have C (constant) & V (variable) C region = same amino acids (from cell to cell) V regions = variable amino acids (from cell to cell) Results in different shapes for different antigens B cells bind to intact, native antigens Secrete antibodies (a.k.a immunoglobulins)
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T Cell Receptor (TCR) has 1 binding site Made of 2 chains: α-chain and β-chain Each chain has C region and V region Tips of V region create different shapes for cells to bind to different antigens T cells bind to broken fragments of antigens 1) From Infected Cell 2) From Phagocyte 2 types of T Cells (but first how get V region?)
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V region is due to combination of different genes leads to diversity of Lymphocytes Looks like alternative splicing Splice in 1 V gene (out of 40) 1 J gene (out of 5) Makes up V region Done for each chain
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Possible that a combination is picked that selects for molecules found WITHIN the body (“not foreign but native antigens”) During development, lymphocytes with receptors for the body’s own molecules are removed or rendered nonfunctional This is called self-tolerance Many autoimmune disorders result form a failure in this system
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B cells Develop in Bone Marrow Binds to intact, native antigens Y-shaped receptors (2 heavy & 2 light chains) = can bind to 2 antigens Secrete Antibodies T cells Develop in Thymus Binds to fragments of antigens 1 α & 1 β chain = bind to 1 antigen Kills or signals others to kill (2 types) Similarities between B cell and T cells Lymphocytes activated by cytokines Have V regions for many antigens, but each cell binds to one type of antigen
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Major Histocompatibility Complex (MHC) molecule: binds to antigen fragments within a cell (infect/digest) then, antigen presentation If cell infected, Class I MHC molecules brings “antigen” to surface for Cytotoxic “killer” T Cells TO KILL whole cell If phagocyte digests, Class II MHC molecules brings “antigen” to surface for Helper T Cells to signal
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So many different B and T cells (own receptor for different antigen), but how many cells for 1 infection? (need lots!) When lymphocyte binds to antigen, triggers clonal selection Activated lymphocyte stimulates division Cloned and differentiates into 2 types 1) Effector cells: short-lived cells that start fighting (how fights depends on…) If B cell = secrete antibody If T cell = kill or send signal to kill 2) Memory cells: long-lived cells w/ receptor
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Primary Immune Response: 1 st time exposed Creates Effectors and Memory Cells Secondary Immune Response Due to memory cells, more effective at responding to antigen the 2 nd time This is how you “develop an immunity” to a disease (i.e. adaptive or acquired imm.)
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B cells secrete antibodies (proteins called…) Immunoglobulins float around in the fluid Type of Humoral Immunity Note: effector cells for B cells are specialized to produce MANY proteins Called Plasma Cells (extensive ER) T cells directly attack or signal to attack Type of Cell-Mediated Immunity Note: effector cells for T cells specialized, but 2 types: helper and cytotoxic What do these guys do again? (effector-wise?)
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http://www.youtube.com/ watch?v=L32Na8fGjzA http://www.youtube.com/ watch?v=1tBOmG0QMbA
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Respond to nearly all antigens, especially fragments from phagocytes; thus, use… Class II MHC molecules Release cytokines to activate B cell (and Cytotoxic T cells / can activate itself, too!) Cell-Mediated So, what do helper T cells actually do? (Effector cells)
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Respond to select antigens that are presented from within an infected cell (cancer, too!); thus, use… Class I MHC molecules Release proteins (granzymes) to destroy cell Creates pores that causes cells to lyse + signal apoptosis Cell-Mediated So, what do killer T cells actually do? (Effector cells)
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http://i.imgur.com/1FYCqNl.gifv
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Bind to intact antigens (float or on surface of pathogen) T-independent antigens Sometimes, activated by Helper T Cells T-dependent antigens (fragments) What do B cells ( effector called? ) actually do? Humoral Effector Plasmid Cells: secrete antibodies So, what do antibodies do?
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Viral Neutralization: bind to block virus from infecting cells Opsonization: enhance ability for macrophages to phagocytize bacteria Activation of complement system (used in) Forms a Membrane Attack Complex (MAC) makes a pore cell lyses Humoral http://www.youtube.com/ watch?v=hQmaPwP0KRI http://www.youtube.com/ watch?v=lrYlZJiuf18
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Active Immunization Person’s own lymphocytes (B & T) create a response (antibodies) Vaccinations (made of dead, dying pathogens or pieces of them - antigens) Passive Immunization Antibodies given to person for a disease triggers destruction of pathogens But will not (by itself) trigger long-lasting immunity no memory cells made Active can happen with passive (depends)…
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