Functions of Antibodies

Question 1

1. Neutralisation: Virus entry
   Bacteria entry
   Toxins

Answer 1

Most of the specificity of certain viruses to a certain cell type is made because the viruses have specific receptors to binding partners on the surface of the cell they are targeting
You can prevent this entry of the virus into the cell by having antibodies which bind exactly to those parts of the of the virus that are needed to enter into a cell
Stop virus from entering

Specific antibodies to the target protein on the surface of the bacterium, will prevent them from entering cells

Bacteria release a toxin which binds to target partners on the surface of the cell to be infected. Toxins enter the cell, change its function and kills cells from inside
Toxin entry can be prevented by specific antibodies to these toxins

Question 2

2. Complement activation

Answer 2

C1q interacts with pathogen surface or with antibodies bound to surface

All pathways generate a C3
convertase, which cleaves C3, leaving C3b bound to the microbial surface and releasing C3a

C3a and C5a recruit phagocytic cells to the site of infection and promote inflammation

Phagocytes with receptors for C3b engulf and destroy the pathogen

Completion of the complement cascade leads to formation of a membrane-attack complex (MAC), which disrupts cell membrane and causes cell lysis

Question 3

3. Opsonisaton: Antibodies can interact with cells through Fc Receptors

Answer 3

2 ways

1. Complement and the antibody together causing the opsonisation.
   Phagocytosis

2.Antibody by itself causing the optimisation
Fc binds to the innate immune cell and the Fab binds to the epitopes of the antigen.

Question 4

4. Immune complexes

Answer 4

Immune complexes can be captured by erythrocytes (RBC) and removed by macrophages

Question 5

5. IgE and type I Hypersensitivity

Answer 5

IgE gets activated by an antigen, cross linking happens, cause degranulation in mast cells and they release histamine.

Question 6

6. Antibody-dependent cellular cytotoxicity

Answer 6

Antibody binds antigens on the surface of target cells

Fc receptors on NK cells recognize bound antibody

Cross-linking of Fc receptors signals the NK cell to kill the target cell

Target cell dies by apoptosis

Question 7

How are Immunoglobulin classes
distributed

Answer 7

IgM- largest antibodies (pentamers), useful in early response, don’t travel much, stay in circulation within blood vessels

IgG- smallest antibodies, travel easily and can be found almost everywhere in body; only antibodies that can travel through the placenta- important for the defence against the early stages of infection in babies

IgA- mucosal surfaces such as GI tract, lungs, urogenital tract

IgE- only tiny amount in circulation, mainly localised on the surface of mast cells

Question 8

Transport of immunglobulin
Mucosal transport; secretory IgA

Answer 8

Dimeric IgA is transported into the gut lumen through epithelial cells at the base of the crypts

Dimeric IgA binds to the layer of mucus overlying the gut epithelium

IgA in the gut neutralizes pathogens and their toxins

Question 9

Transport of immunglobulin
Placental transport; IgG

Answer 9

IgG Antibody is transported from the mother to the fetus across the placenta

The FcRn transports only IgG to the fetus

Question 10

Production of monoclonal antibodies

Answer 10

Side 23, 24