T4L6 - B cells and antibody

Question 1

Antigen-specific definition

Answer 1

The antibody binds to a particular antigen (eg measles) with high affinity, but not to other antigens (eg pneumococcus)

Question 2

Antigen binding site

Answer 2

(FAB) is made up of light chains and heavy chains
VARIABLE
Antibodies recognise epitopes

Question 3

Antibody isotopes

Answer 3

Different heavy chains

Question 4

B cells and antibodies

Answer 4

Antibodies attach to cells at Fc region

Each B cell produces 1 antibidy

Question 5

IgA

Answer 5

Found in secretions - gut, tears and saliva
Forms dimers
Secretory component

Question 6

IgM

Answer 6

1st produced
Low affinity for antigen
Pentamers

Question 7

Opsonisation

Answer 7

Bacteria coated by circulating antibody
Phagocytic cells have receptors for the Fc portion of the antibody
This enhances phagocytosis by reducing the repulsion between two negatively charged membranes

Question 8

Mast cell activation

Answer 8

Cells have Fc receptors
Coated with IgE
Antibodies crosslink and degranulate them
Histamine released

Question 9

Somatic recombination advantages

Answer 9

Huge diversity – we can recognise whatever is in our environment
A large numbers of receptors can be made from a smaller area of DNA
Everybody has a unique repertoire – resilient in different environments/ against emergent pathogens
Still inherit the gene segments, so get some benefit from evolutionary experience

Question 10

Somatic recombination disadvantages

Answer 10

• The receptors are generated at random - many combinations will not work out:
○ Some can’t fit together biochemically
○ Some will bind to our own proteins (self antigens)
• B cells with dysfunctional receptors mostly destroyed (deleted) – process is therefore energy intensive
Deletion of B cells that can recognise self-antigens is not complete – potential for autoimmune disease

Question 11

Clonal selection .

Answer 11

We all start with a unique set of B cells, each producing a single antibody; small number of each B cell

Best one chosen

Question 12

Affinity maturation

Answer 12

1. Class switch: IgM in the ‘primary response’ switches to IgG. The variable region of the antibody remains the same
2. Somatic hypermutation: Random mutations are introduced into the variable region of the antibody, so the daughter cells produce a slightly different antibody. Further rounds of clonal selection pick out the best receptors