Lecture 9 - Recognition -Immune System-1

Destroys and remembers foreign parasites while

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destroys and remembers foreign parasites while ignoring the host’s cells and proteins • Recognizes foreign molecules = Antigen – B cells release Immunoglobulins to circulation – T cells have T cell Receptor that recognizes when presented on MHC class 1 protein
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Antibodies: Immunoglobulin G Composed of two heavy chains and two light chains Composed of constant domains and variable domains Light chains: one constant and one variable domain Heavy chains: three constant and one variable domain Variable domains of each chain make up antigen binding site (two/antibody) Variable domains contain regions that are hypervariable (specifically the antigen binding site) Confers high antigen specificity
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Antibodies: Immunoglobulin G
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Antibodies: Immunoglobulin G
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Immunoglobulin Molecule - IgG • Heterotetramer – 2 Light chains +2 Heavy chains – Linked by 4 disulfide bonds – Hinge region of HC gives flexibilbity • Ig fold is distorted barrel – Each LC contains 2 Ig folds – Each HC contains 4 Ig folds – Distored conformation stabilized by intrachain disulfide bridges • Antigen recognition at loops between strands at N-terminus of Ig
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IgG cleavage by Papain enzyme 150 kDa 50 kDa each
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Each IgG recognizes only 1 antigen • Each B cell generates 1 type of Ig that recognizes 1 antigen • HC and LC are different genes • DNA for complete Ig arises from combinatorial joining of exons • Regions at N terminus are most variable
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Immunoglobulin Fold
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Constant and Variable Domains
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V L and C L
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IgG Antigen Recognition at Loops
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MHC proteins present peptides of foreign proteins for T Cell Receptors on T cells
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MHC class 1 and 2 • Recognition motif is 2 helices + 2 antiparallel sheets • Recognition motif connected to TM domain by sandwich • IgG-like domains and • MHC class 1 is monomeric • MHC class 2 is dimeric
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Recognition Motif of MHC • All TCRs recognize helices of MHC • Foreign peptide lays in cradle between helices • High specificity binding of TCR to foreign peptide within MHC cradle
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MHC Peptide Presentation
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TCR binding to MHC class I
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MHC-1 peptide-T-cell R complex
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