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22 Cards in this Set
- Front
- Back
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Antibody
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- larger MW than TCR
- 2 binding sites for Ag on arm - hinged region connecting arm to stem - Bind intact Ag - can be secreted or membrane bound - 5 classes, G, M, A, D, E |
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Constant Region
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Determines how the Ab disposes of the pathogen once it is bound.
5 main constant regions (classes/isotypes) (G, M, A, D, E) |
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T - Cell Receptor
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- smaller MW than Antibody
- One binding site binds Ag fragment and MHC - 2 types alpha/beta and gamma/delta - Always on membrane |
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Antibody Structure
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- Y shaped
- Arms of the Y are variable regions (has 2) - stem of the Y is the constant region - The arms and stem are connected with a hinge region. |
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Variable regions
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Determines the Ag-binding specificity.
- There are 2 heavy and 2 light protein chains linked by disulfide bridges. - They are identical within the particular Ab. - This gives bivalent binding sites. - The paired variable region (L and H chains) form the antigen binding site. |
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Papain
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A protease that cuts the hinged region of Ab above the bridge resulting in 3 fragments
- 2 fragment antigen binding sites (Fab) - 1 fragment crystalizable (Fc) receptor |
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Pepsin
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A protease that cuts the hinged region of Ab below bridge.
- 2 fragments 1 Fab and 1 Fc |
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Ab:Ag binding
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Abs bind to the conformational shapes on the surface of Ag (at the epitope)
- Binding is non-covalent and therefore reversible. |
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Types of Ab:Ag binding
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1. Electrostatic interactions
2. H-bonds 3. Van der Waals forces 4. Hydrophobic interactions |
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What is the problem with covalent bonds?
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The protein would have to be destroyed in order to break the bonds.
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3 Main Effector Functions of Ab's
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1. Neutralization
2. Opsonization 3. Complement Activation |
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2 Classes of MHC
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1. Class 1 = molecules collect peptides from the cytoplasm and are presented to CTL. Stabelized by CD8 cell surface protein.
2. Class 2 = molecules collect peptides from vessicles and are presented to Th cells. Stabelized by CD4 cell surface protein. All are highly polymorphic in order to bind different peptides. Remember 1 x 8 and 2x 4 MHCI = CD8 MHCII = CD4 |
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T cells with different functions are distinguished by:
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CD4 and CD8 cell surface proteins.
CD4 = Th marker CD8 = CTL marker |
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Antigenic vs. Immunogenic
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Antigenic = an agent that binds specifically to preformed Ab or T-cell... Is recognized by the immune system.
Immunogenic = an agent capable of inducing an immune response. Stimulates immune system. |
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MHCI
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INTRACELLULAR
- All cells (except RBC) express MHC since they are all susceptible to viral infection. - 1 tail - binds shorter peptides (8-10) - takes peptides from cytosol to ER - leads to cell death. |
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MHCII
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EXTRACELLULAR
- Only professional APCs express MHCII (dendritic, macrophage, and B-cells) since endocytosis is involved.. - 2 tails - binds longer peptides (13-17) - takes peptides, that have been internalized by endocytosis, from vesicles to cell surface. - activates B-cells to secrete Ab to eliminate bacteria/toxins. |
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IgG
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- Most abundant of all the Ig classes
- IgG is good at neutralizing toxin - IgG is the main antibody found in the secondary immune response - IgG is a monomer and has 2 epitope-binding sites - The Fc portion of IgG can activate the classical complement pathway, can bind to macrophage and neutrophils for enhanced phagocytosis, can bind to NK cells for antibody-dependent cytotoxicity or ADCC - The Fc portion of IgG enables it to cross the placenta. (IgG is the only class of antibody that can cross the placenta and enter the fetal circulation.) |
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IgM
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- IgM monomer is the B-cell receptor of the mature B-cell
- IgM is the first antibody made in an immune response – about 7 to 10 days after initial exposure - IgM is the first antibody made in life – about 5 months in utero - the first antibody produced during an immune response. - IgM is a pentamer and has 10 epitope-binding sites (see Fig. 2). - The Fc portions of IgM are able to activate the classical complement pathway. IgM is the most efficient class of antibody for activating the classical complement pathway. |
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IgA
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- IgA is important for passively acquired immunity of nursing baby.
- IgA is found mainly in body secretions (saliva, mucous, tears, colostrum and milk) as secretory IgA (sIgA) where it protects internal body surfaces exposed to the environment by blocking the attachment of bacteria and viruses to mucous membranes. - IgA is made primarily in the mucosal-associated lymphoid tissues (MALT). - IgA appears as a dimer of 2 "Y"-shaped molecules and has 4 epitope-binding sites and a secretory component to protect it from digestive enzymes in the secretions - The Fc portion of secretory IgA binds to components of mucous and contributes to the ability of mucous to trap microbes. - IgA can activate the lectin complement pathway and the alternative complement pathway |
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IgE
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- IgE is made in response to parasitic worms. When bound to the parasite, it triggers a very strong inflammatory response to the worms.
- IgE is the antibody that triggers allergy - IgE binds to Fce receptors on the surface of mast cells - Most IgE is tightly bound to basophils and mast cells via its Fc region - IgE is a monomer and has 2 epitope-binding sites. - IgE may protect external mucosal surfaces by promoting inflammation, enabling IgG, complement proteins, and leucocytes to enter the tissues. |
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IgD
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- IgD is a monomer and has 2 epitope-binding sites.
- IgD is found on the surface of B-lymphocytes (along with monomeric IgM) as a B-cell receptor or sIg where it may control of B-lymphocyte activation and suppression. - IgD may play a role in eliminating B-lymphocytes generating self-reactive autoantibodies |
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Adaptive immunity is triggered... ?
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when the pathogen dose reaches a threshold level.
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