antibody structure and the generation of b cell
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Antibody Structure and the Generation of B - Cell Diversity
Dr. Glorivee Rosario Pérez
BIOL 4056
Parham P. (2009). The Immune System. Third Edition. Garland Publishing, New York.
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Introduction
Antibodies Proteins Produced by the B lymphocytes in response to
infection They circulate as a major component of the plasma in
blood and lymph Their function is to bind to pathogenic microorganisms
and their toxins (antigens) Are specific
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Introduction cont.
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Figure 3-1
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Introduction cont.
Antibody production is the single effector function of the B lymphocytes of the immune system.
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The structural basis of antibody diversity
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Antibodies : Variable and Constant region
N-terminal
C-terminal
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Antibodies : Variable and Constant region cont.
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Antigen-binding site
Hypervariable regions (HV regions) Small regions of high amino-acid sequence diversity
within the variable regions of immunoglobulin and T-cell receptor.
They correspond to the complementarity-determining regions.
Complementarity-determining regions (CDRs)
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Antibodies : Variable and Constant region cont.
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Antibodies : Variable and Constant region cont.
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Immunoglobulin chains
Immunoglobulin domain
Components of protein structure consisting of about 100 amino acids that fold into a sandwich of two β sheets held together by a disulfide bond.
Immunoglobulin heavy and light chain are made up of a series of immunoglobulin domains.
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Immunoglobulin chains cont.
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Antigen-binding site Hypervariable regions
(HV regions) Small regions of high
amino-acid sequence diversity within the variable regions of immunoglobulin and T-cell receptor.
They correspond to the complementarity-determining regions.
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Antigen-binding site cont.
Complementarity-determining regions (CDRs)The localized regions of immunoglobulin and
T-cell receptor chains that determine the antigenic specificity and bind to the antigen.
The CDRs are the most variable parts of the variable domains and are also called hypervariable regions.
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Antigen-binding sites
Antigenic determinant (epitope)The part of the antigen to which an antibody
binds.These structures are usually either
carbohydrate or protein, or both, because the surface molecules of pathogens are commonly glycoproteins, polysaccharides, glycolipids, and peptidoglycans.
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Figure 3-8
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Antigen-binding sites cont.
Multivalent antigen – any antigen that contains more than one epitope, or more than one copy of the same epitope.
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Antigen-binding sites cont. The binding of antigens to antibodies is based on
noncovalent forces:
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Generation of immunoglobulin diversity in B cells before encounter with antigen
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Gene segments
Multiple short DNA sequences in the immunoglobulin and T-cell receptor genes.
These can be rearranged in many different
combinations to produce the vast diversity of immunoglobulin or T-cell receptor polypeptide chain.
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The organization of the human immunoglobulin heavy- and light-chain loci
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Figure 4-3
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Gene segments (V)
Variable (V) gene segments DNA sequence in the immunoglobulin or T-cell
receptor genes that encodes the first 95 or so amino acids of the V domain.
There are multiple different V gene segments in the germINAL genome.
To produce a complete exon encoding a V domain, one V gene segment must be rearranged to join up with a J or a rearranged DJ gene segment.
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Gene segments (J)
Joining (J) gene segmentsOne of the types of gene segment in
immunoglobulin and T-cell receptor genes that is rearranged to make functional variable-region exons.
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Gene segments (D)
Diversity (D) gene segmentsShort DNA sequence present in
immunoglobulin heavy chain loci and in T-cell receptor β- and δ-chain loci.
In the rearranged functional genes at these loci, a D region connects the V and J region.
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Mechanisms contributing to the diversity in V-region1. Random combination of different V and J segments
in light chains genes and of different V, D, and J segments in rearranged heavy chain genes.
2. Introduction of additional nucleotides at the connections between gene segments during the process of recombination.
3. Diversity in the antigen-binding sites of antibodies is the association of heavy and light chains in different combinations.
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1. Random recombination of gene segments produces diversity in the antigen-binding sites of immunoglobulins
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Figure 4-2
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Figure 4-13
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Naïve B cells
A mature B cell that has left the bone marrow but has not yet encountered its specific antigen.
IgM and IgD
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Expression of IgM and IgD
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Allelic exclusion
In a developing B cell, the process of immunoglobulin-gene rearrangement is controlled so that only one heavy chain and one light chain are finally expressed.
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Membrane-bound immunoglobulins
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Diversification of antibodies after B cells encounter antigen
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Secreted antibodies
Mature cell (naïve cell)
IgM IgD(membrane-bound)
antigen
(secreted antibodies)↑↑↑IgM ↑IgD
antigen
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The surface and secreted forms of an immunoglobulin
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Somatic hypermutation
Mutation that occur at high frequency in the rearranged variable region DNA of immunoglobulin genes in activated B cells, resulting in the production of variant antibodies, some of which have a higher affinity for the antigen.
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Isotype switching
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The physical properties of the human immunoglobulin isotypes
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Figure 4-18
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Figure 4-23
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Antibody function : IgM
Is the first antibody produced in an immune response.
It is made principally by plasma cells resident in:Lymph nodesSpleen (BASO)Bone marrow
Circulates in blood and lymph.
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Antibody function : IgG
Is the most abundant antibody in the internal body fluids, including blood and lymph.
It is made in the: Lymph nodes Spleen Bone marrow
Is smaller and more flexible than IgM, properties that give it easier access to antigens in the extracellular spaces of damaged and infected tissues.
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Antibody function : IgA
Is made by plasma cells in: Lymph nodes Spleen(HIGADO) Bone marrow
Is secreted into the bloodstream. Dimeric IgA is made in the lymphoid tissues
fundamental mucosal surfaces. Is the antibody that is secreted into the lumen of
the gut. Principal antibody of milk, saliva, sweat, and
tears.
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Antibody function : IgE
Is highly specialized towards the activation of mast cells, which are present in epithelial tissues.
The major impact of IgE is in the allergies that result when it is produced against antigens.
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Mechanisms by which antibodies combat infection
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Functions and properties of immunoglobulin
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Applications: Antigen-Antibody
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Figure A-1
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Figure A-5
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Figure A-6
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Figure A-7
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Figure A-8
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Figure A-9
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Figure A-10
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Figure A-13
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Monoclonal antibodies
The traditional method for making antibodies of desired specificity is to immunize animals with the appropriate antigen and then prepare antisuero from their blood.
antisera
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Monoclonal antibodies cont.
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Monoclonal antibodies cont.
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Figure A-15
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Radioimmunoassay (RIA)
FIGURA 18.37
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Figure A-18Radioimmunoassay (RIA) cont.
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Figure A-20
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Figure A-22
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Figure A-23
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Figure A-26
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Figure A-29
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Figure A-40
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Figure A-41
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Figure A-16Immunofluorescence
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Figure A-17Immunofluorescence cont.
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FIGURA 18.35
Immunofluorescence cont.
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FIGURA 18.38
Immunofluorescence (ELISA) cont.
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FIGURA 18.39
Immunofluorescence (Western Blot) cont.
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Flow cytometry
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Figure A-25 part 2 of 2Flow cytometry cont.