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B cells and their products
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Lecture 6 – B Cells and Their ProductsCells of the Adaptive Immune System
Lymphocytes= relatively small when at rest. Little cytoplasm when in resting state.
T Cells Vs B Cells [Cellular Vs Humoral]
Express receptors= B Cell Receptor (BCR) and T Cell Receptors (TCR).
B Cells
o 2 binding regions.
o Membrane or soluble bound.
o Have co-receptors.
o 4 chains.
T Cells
o 1 binding region.
o Membrane bound.
o Has co-receptors.
o 2 chains.
BCR and Antibody
B Cells:
Have an antigen binding region at the top.
They are a membrane-bound ig.
Antigen-specific receptor (BCR).
Recognising molecule.
Alpha and beta chains for signalling.
BCR signals through CD79A and B.
Antibody:
Antigen binding site at the top.
Secreted ig.
Antigen-specific soluble protein.
Effector molecule.
Antibody
Have a variable light chain (i.e., VL) and constant heavy chain domains (i.e., CH1).
Heavy chain= gamma, alpha, beta.
Light chain= kappa or lambda.
Light chains have 2 domains.
Heavy chains 4-5 domains depending on the
antibody.
Antibody Structure
Can be elucidated using this example:
Ovalbumin Antibodies to ovalbumin in serum. serum
alone OR serum + ovalbumin precipitates.
, Summary of Antibody Structure Experiments
Fc does not bind an antigen.
Fab and F(ab’)2 fragments do bind an antigen.
Papain= splits into 3 fragments – 2x Fab and an Fc.
Pepsin= splits into a F(ab’)2 fragment and degrades Fc.
ME= breaks disulphide bonds to give 2x heavy and 2x light chains.
Precipitated Antibody and Antigen Complexes
- Bivalent antibodies binding to repeating antigenic structures produce immune complexes that is in
equilibrium.
- Equilibrium is not achieved if there is an excess of antibody or an excess of antigen.
Motion Within mAbs
Complementarity Determining
Region (CDR’s)= Part of variable
chains in immunoglobulins
(antibodies) and T cell receptors.
A set of CDR’s constitutes a
paratope.
Hypervariability in the V Regions
- Number of different amino
acids/frequency of the most common.
- CDR’s 1, 2 and 3 present in each VH and VL domain.
- Hypervariable regions are CDR’s.
After an antigen binds there is a conformational change in the antibody. 6 CDR’s make up the antigen-binding
site on an antibody.
Antibody Isotypes
Isotype= refers to the nature of the heavy chain of an antibody.
5 major isotypes:
IgM [mu heavy chain].
IgA [alpha heavy chain].
IgG [gamma heavy chain].
IgD [delta heavy chain].
IgE [epsilon heavy chain].
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