28 BIO 326R B cells - BIO 326R B cells Antibodies basic...

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    BIO 326R B cells
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    Antibodies – basic structure Heavy chain Light chain Variable region (heavy + light chain) Constant region (heavy + light chain) Basic antibody structure consists of 4 polypeptide chains – 2 light chains and 2 heavy chains. The light chains have an identical amino acid sequence to each other, as do the heavy chains. The tetramer is held together by disulfide bonds. The variable region binds antigens. The variable region consists of a portion of both the heavy light chains (usually, both make contact with antigen). There are 2 variable regions, thus the antibody can bind two antigens simultaneously. The constant region (sometimes called Fc, also called effector region) is recognized by some immune cells and other molecules. Usually, many antibody functions are determined by the heavy chain constant region.
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    Antibodies Antibodies are a large protein made in response to an antigen “antigenic challenge” Purified antibodies from a human individual will contain 5 subtypes: M, A, D, G and E IgM, IgA, IgD, IgG and IgE It’s a little more complex than that as there are 4 different IgGs and two different IgAs, for 9 total, plus secreted and membrane bound versions of each There are also two light chains, kappa and lambda . Either of these can be used with any heavy chain. If you test serum for antibodies to a given antigen (e.g. Hen Egg Lysozyme or HEL) you will not be able to detect any specific binding of antibody to the antigen (assuming they’ve never been exposed to the antigen before) Injecting some of the HEL (a challenge) into the individual changes that Over the course of a few days, increasing amounts of antibody will be able to bind to the HEL. Not only will the amount of antibody increase, but the affinity they have for HEL will increase (they will bind more tightly) Somehow, the B cells have learned to make antibodies that bind to HEL If no further HEL is introduced, then Ig levels will decline to near zero again. Administering a second challenge of HEL will cause a more rapid production of anti-HEL antibody, but this time we will see a very fast production of large amounts of highly specific IgG (IgM will also be made). Somehow, the B cells have remembered how to make anti-HEL antibodies B cells are able to assemble variable regions which can tightly bind to virtually any antigen, and then subsequently have this variable region attached to different constant regions
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    Antibodies Day 7 14 Secondary Challenge IgG IgM affinity Primary Challenge Specific Ab from blood of mouse (or human) 2
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    B cells can change the antibodies they  produce Initial (naïve) antibodies IgM Low affinity Specific antibody IgM Higher affinity Highly specific, high affinity IgG or IgE or IgA Affinity maturation Class switching
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    The Immunoglobulin Heavy Chain (IgH)  locus, 14q32 p arm q arm centromere
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    Human IgH locus – not to scale
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This note was uploaded on 07/24/2009 for the course BIO 52035 taught by Professor Edsatterwhite during the Spring '08 term at University of Texas at Austin.

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28 BIO 326R B cells - BIO 326R B cells Antibodies basic...

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