Antibody interaction with antigen Flashcards
(45 cards)
What does the Ab recognise?
Conformational antigens composed of several sequentially discontinuous segments brought together by folding of the molecule
What is the epitope?
The part of the antigen which is recognized by the antibody
What is the paratope?
The complimentary part of the antibody
What is each V region made of?
3 hypervariable regions
What are complimentary determining regions?
6 hypervariable regions of light and heavy chains
Describe the hypervariable region
CDR loops interact with antigen
Poke out of the beta sheets of Ig domain
How does the binding happen?
Neither the antibody nor the antigen is changed by binding
One antibody binding site binds to one epitope on the antigen
The binding is non-covalent and is reversible
What bonds are involved in the binding?
Non-covalent interaction due to Ionic bonds
H-bonds
Hydrophobic bonds
Van der Waals forces
Lots of small forces add up to a strong interaction.
All critically dependent on the distance apart
What forces are present in antibody-antigen binding?
Electrostatic
Hydrogen bonds
Hydrophobic bonds
Van der Waals
What is the strength of interaction?
Each force acts over short distance that can be measured (affinity)
What is meant by avidity?
Avidity = total binding strength
Different from affinity (binding strength at a single binding site)
Avidity functionally more important than affinity
What else is required for antibody production?
Additional signals from the B cell once BCR is ligated and IgAlpha and IgBeta signal is sent
How do T cells contribute to Ab production?
Cytokine production
What does neutralisation of viruses depend on?
type of virus, target cell and class of Ab
What is the importance of antibodies in neutralisation?
May be important in limiting viral infectivity - bind to a virus to block infection
Vaccine efficacy often assessed by measuring circulating, neutralising Abs
Why is neutralisation important?
May inhibit virus-cell interaction
Prevent endocytosis of virus
Prevent uncoating inside endosome
What makes neutralisation more effective?
Complement
How are toxins neutralised?
Abs bind bacterial exotoxins: neutralise their effect by preventing attachment to cellular receptors (e.g. binding of cholera toxin to ganglioside GM1)
What antibodies are important in neutralisation?
IgG and IgA
What receptor mediates toxin clearance?
Fc-receptor
What is opsonisation?
The coating (binding) of particles by either Ab,
complement or APP (eg CRP)
Ab bind microorganisms via the Fab and to cells
by the Fc
What does opsonisation do?
Increases the efficiency of the
phagocytic process, allowing the organism to be
cleared more effectively
What is complement?
The complement system is a collection of circulating membrane-associated proteins
Important in defence against microbes
What are the pathways of complement?
Classical and alternate pathways
