B cells and Antibodies

Question 1

Draw and label an antibody (immunoglobin) (5)

Answer 1

Allocate:

1. Identical Heavy chains (x2)
2. Identical Light Chains (x2)
3. Constant and variable region
4. Antigen bind sites (x2) (FAB)
5. Fc Region which interacts with other components of the immune system.

Question 2

How do antibodies recognise antigens? (1)

Answer 2

Antibodies recognise ‘epitopes’ (determining component on antigen) using variable region.

Question 3

What are the differences between antibody isoptopes? What are the 5 types?

Answer 3

1. The heavy chain constant regions differs which changes properties and function. The isotopes still bind to the same antigen as variable region stays the same.

Pseudonym: MADGE.
2. IgM, IgA, IgD, IgG, IgE

Question 4

Describe IgM features (2)

Answer 4

1. It is the first antibody produced in immune response, but switches to other isotopes as immune response progresses.
2. It has low affinity, however forms PENTAMERS, held by a J chain to make up for it.

Question 5

Describe IgA features and where it is found. (3)

Answer 5

1. Only antibody that can cross MUCOSAL surfaces. Hence found in secretions e.g gut, tears, saliva.
2. Forms dimers joined by a J chain. This is protected from digestion by S chain (secretory component).
3. Colostrum (forerunner of breast milk) rich in IgA antibody.

Question 6

Describe IgD, IgG, IgE. (3)

Answer 6

IgD: Like IgM, first antibody produced by B cell, unknown function.

IgG: Main Mature Antibody, circulates as monomer.

IgE: Important in Allergy and maybe parasitic infection, exact function unknown. Circulates as monomer.

Question 7

What are the main functions of antibodies? (3)

Answer 7

1. Binding to antigens. Such as in toxin neutralisation (e.g tetanus toxin), receptor blocking (e.g virus).
2. Activating other immune response e.g phagocytosis, mast cell activation etc.
3. Act as receptor when on B-cell

Question 8

What is Opsonisation? (2)

Answer 8

1. When antibodies coat bacteria to enhance phagocytosis by reducing repulsion between two negatively charged membranes (bacteria and phagocytes).
2. The antibody Fc region binds to phagocyte, and variable region binds to bacteria.

Question 9

Antibody activates Mast Cell and what is released? (2)

Answer 9

1. IgE activates Mast Cell, attaches to corresponding antigen.
2. The mast cell ‘degranulates’ releasing histamine. This activates inappropriately during allergy.

Question 10

How do NK cells recognise the correct bacteria to destroy? (2)

Answer 10

NK cells recognise the antibody which coat the bacteria, attaching to the Fc region of the antibody.

Question 11

What is the ‘complement’ system in immunity? What are 3 examples? (3)

Answer 11

When antibody attaches to antigens and trigger a cascade of reactions for further immune action.

Examples: Opsonisation, Inflammation terminal attack pathway

Question 12

How are is diversity in the variable region/receptor of antibodies regenerated from DNA?

Answer 12

1. By Somatic recombination.

2. A gene segment is taken from multiple genes at random and combine to form variable region of the antibody.

Question 13

What are the advantages of Somatic Recombination? (2)

Answer 13

1. Huge diversity and large number of receptors can be made from smaller DNA area.
2. It makes antibodies unique based on pathogens in individual environment.
3. Can be inherited.

Question 14

What are the disadvantages of Somatic Recombination? (3)

Answer 14

1. Due to random generation, dysfunctional receptors may arise.
2. Dysfunctional receptors will need to be destroyed which is energy intensive.
3. Dysfunctional receptors may bind to our own proteins causing Autoimmune disease.

Question 15

What is Clonal Selection? (2)

Answer 15

During primary infection, the immune system selects, and proliferates the B-cells with antibodies that have the best response to the antigen.

Question 16

What is affinity maturation? (2)

Answer 16

Following clonal selection, as the fittest B-cells increase:

1. Class switch: The IgM first response changes to IgG.
2. Somatic Hypermutation: Random mutations in variable region, so daughter cells have slightly different antibodies, this improves affinity.

Question 17

What does it mean for the Immune system to have Memory?

Answer 17

1. Once B cells have undergone clonal selection and affinity maturation, the updated IgG B cells become long-lived Memory cells.
2. When same antigen is presented again, the B cells respond quickly and vigorously. This is the secondary immune response.