LW - Antigens and antibodies, structure and interaction Flashcards
What is the definition of an antigen?
A substance which binds to a lymphocyte receptor and in doing so may initiate an immune response.
What is an autoantigen?
Antigens part of the normal body.
What is an alloantigen?
Cells from the same species but genetically different.
What is a xenoantigen?
Cells from different species.
Why can one substance be more antigenic than another?
- 1 antigen may have several epitopes.
- 1 of which could be immunodominant.
What is an epitope?
A part of the antigen that causes an immune response.
What is a hapten?
A small chemical group, which when chemically conjugates to a larger protein will alter its specificity creating a new epitope.
What is an immunogen?
A substance that induces and immune response when injected into an individual.
What factors determine immunogenicity?
- Method of preparing the antigen.
- Species and strain of the recipient.
- Dose of antigen.
- Route of administration.
- Use of adjuvant.
What is an adjuvant?
A substance, which when combined with an antigen, non-specifically enhances the immune response.
May also cause slow release of an antigen
What are the 5 classes of immunoglobulin?
IgA, IgE, IgM, IgD, IgG
Describe the structure of IgG.
Single y-shaped unit.
Valence = 2
Gamma heavy chain.
What is the function of IgG?
Main Ig found in the body. Diffuses easily. Neutralises toxins. Main Ig in a secondary immune response. Fixes complement. Enhances phagocytosis.
Describe the structure of IgM.
5 y-shaped units. Valence = 10 Mui heavy chain. Extra heavy chain - CH4. J chain helps to link all of the units
What is the function of IgM?
Agglutinates particulate antigen. Fixes the complement. Main Ig in the early immune response. Intravascular - stays in the blood. Important in bacteraemia.
Describe the structure of IgA.
Can exist as a monomer or a dimer - dimer in mucosal secretions.
Dimer is linked by J chains. And at the mucosal surface has a ‘secretory piece’, this provides protection from enzymatic degradation.
Valence = 2/4
alpha heavy chain
What is the function of IgA?
Mucosal immune defence. Inhibits microbial attachments. Neutralises toxins. Weak opsonin. There are further subclasses.
What does opsonin mean?
An antibody or other substance which binds to foreign microorganisms or cells making them more susceptible to phagocytosis.
Describe the structure of IgD.
1 y-shaped unit.
Valence = 2
Delta heavy chain.
What is the function of IgD?
- Found on the surface of immature B-cells.
- No clear function.
Describe the structure of IgE.
1 y-shaped unit.
Valence = 2
Epsilon heavy chain.
What is the function of IgE?
- Low level in serum.
- Mostly bound to mast cells of blood basophils.
- Parasite rejection and allergies.
What determines antibody affinity?
The attractive force between the antigen and the antibody.
What is antibody avidity?
The measure of the total binding strength of an antibody. Taking into account each binding site.
Describe how an antigenic epitope binds to an antibody.
The antigenic epitope slots into a groove formed between the hyper variable regions of the heavy and light chains.
After pepsin acts on an antibody, which regions are left?
1 x Fab’2
1 x Fc
After papain acts on an antibody, which regions are left?
1 x Fc
2 x Fab
