W3L6 - Antibody Function

Question 1

What is the primary function of Antibodies?

Answer 1

Antibodies stick to target molecules and epitopes on antigens

Question 2

Biological role of Antibody/Antigen interactions

Answer 2

Activation of complement
Antibody Dependent cell-mediated cytotoxicity
Passive immunity 
Neutralisation
- toxins
- viruses
Opsonisation
Agglutination

Question 3

Activation of Complement

Answer 3

Complement system consists of a series of plasma proteins that are part of innate immune system
Functions of the complement 
- Induce cell lysis (formation of membrane attack complex)
- to promote an inflammatory response
- promote phagocytosis
- remove immune complexes
3 activation pathways
- Classical
- Alternative
- Lectin

Question 4

Activation of Complement - Classical Pathway

Answer 4

Cell lysis is via classical pathway
Cascade of biological reactions leading to formation of membrane attack complex
Initiated by antibody/antigen binding (IgG and IgM)
Complement binds to antibodies, causes lysis by putting holes in cell causing it to swell and burst

Question 5

Antibody Dependent cell-mediated Cytotoxicity

Answer 5

NK cells detect antibody coated cells via exposed Fc receptors
- a mechanism for the removal of tumour cells and virally infected cells
- release toxic granules to kill the target cell
Antibody isotope only IgG
NK cells can also target a cell by recognising the absence of surface MHC class 1 molecules

Question 6

Passive Immunity - Placental Transfer

Answer 6

Maternal transfer of immunoglobulins from mother to foetus
1-3 months prior to birth foetus makes own IgM
Antibody isotope given by mother only IgG - subclasses IgG1, 3, 4 not 2
Newborns only make their own IgG around 3-4 months after birth
One negative
- haemolytic disease of newborn is mothers Abs react with foetus RBC

Question 7

Passive Immunity - Anti-venom

Answer 7

Antibodies against a particular venom (antigen) are administered to an affect patient
Antibody isotope only purified IgG

Question 8

Neutralisation of Toxins

Answer 8

Prevents the binding and entry of the toxin into the target cells
Neutralisation of venom following passive administration
Antibody isotope - IgG
Removal of the antigen antibody complexes formed by phagocytosis or complement

Question 9

Neutralisation of Virus Particles

Answer 9

Antibodies bind to the surface of antigens of a virus particle
Blocks adhesion of the virus to the mucosal epithelium/cell membrane
- prevents viral entry into the cell
Antibody isotopes - IgM, IgA, IgG

Question 10

Antibody Opsonisation

Answer 10

Opsonisation is the process of an antibody binding to an epitope on an antigen molecule located on a target microorganism/particle, coating the particle and marking it for destruction by phagocytosis
Coated molecule known as the opsonin 
Phagocytes involved
- macrophages
- PMN
Antibody isotope - only IgG

Question 11

Immunoglobulin E

Answer 11

Least abundant isotope
Main function is the immune response to parasites
- once manufactured, IgE binds to surface of parasites
- Fc receptors on eosinophils and mast cells bind to Fc portion of IgE
- degranulation of eosinophils

Question 12

IgE and Allergies

Answer 12

Allergic response is usually an inappropriate IR

• can trigger very powerful inflammatory reactions
• primary IR to allergen = IgE bound to basophils/mast cells
• secondary IR to allergen = degranulation/release histamine

Question 13

Immunoglobulin D

Answer 13

Expressed on mature B cells together with IgM
Functions as an antigen specific B-cell receptor for B cell activation i.e. binding of antigen stimulates B cell to become either a memory B cell or plasma cell
- when stimulated, a memory B cell converting to plasma cell undergoes isotope switching to IgM or or IgG, IgA, IgE (requires T cell help)