Week 124 - Vaccination

Question 1

What is the MHC?

Answer 1

The major histocompatability complex.

Located on chromosone 6, is a selection of genes that play an important role in immune function.

The genes are known as human leucocyte antigens (HLC), they code for proteins expressed on the surface of a variety of cell types that are involved in antigen recognition.

Question 2

What are the collection of genes that are responsible for producing proteins involved in antigen recognition?

Answer 2

Human leucocyte antigens.

Located in the majority histocompatability complex (MHC) on chromosone 6.

Question 3

There are three classes of of HLA genes, what are they?

Answer 3

1) Classical class I HLA genes - These present to CD8 T-Lymphocytes.
2) Non-classical HLA class I genes - These are predominantly found on epithelial cells and signal cellular stress and interact with NK cells.
3) The class II genes - These present to CD4 T-Lymphocytes.

Question 4

What are the two main types of immunity? Give an example of natural and induced for each.

Answer 4

1) Active-
- Natural - Exposure to infective agents or diseases.
- Induced - Using live or attentunated live organisms or their products.

2) Passive-
- Natural - Mother to child.
- Induced - Injection of immunogloblins.

Question 5

What are the two stages of active immunity and how do they differ?

Answer 5

1) Primary antibody response - Small response, memory cells produced.
2) Secondary antibody response - Rapid and effective response.

Question 6

What is the difference between a relative and absolute contraindication?

Answer 6

An absolute contraindication is contraindicated in all circumstances, whereas a relative contraindication is inadvisable but may be used in certain situations.

Question 7

In which situations should an immunisation be deferred?

Answer 7

1) Acutely unwell with systemic symptoms or fever.
2) Evolving neurological condition.

Question 8

Which conditions are **not **contraindicated for routine vaccination?

Answer 8

Eczema, asthma, hayfever, febrile convulsions or epilepsy, family history of any of the above.

Question 9

Should a child taking prednisolone be given a routine vaccination?

Answer 9

Depends on the vaccine.

Live vaccines should not be given to people who are immunosupressed, but attenuated or immunoglobulin vaccinations are ok.

Question 10

Are vaccines contraindicated based on a previous confirmed anaphylactic reaction to the vaccine?

Answer 10

Yes, if it contains the same antigens or a component which has previously caused anaphylaxis.

Question 11

What are the two main antigen-presenting cells?

Answer 11

Macrophages and dendritic cells.

They also secrete cytokines that stimulate the immune response.

Question 12

What is required for a TcR to recognise a processed antigen?

Answer 12

They must be a **specific **non-self antigen and they must be bound to an MHC molecule on an antigen-presenting cell.

Question 13

Which type of T-cell binds to MHC class II?

Answer 13

CD4+, T-helper cells.

Question 14

Which type of T-cell binds to MHC class I?

Answer 14

CD8+, T-killer cell.

Question 15

Where are the MHC class I and class II molecules located?

Answer 15

• Class I - on all nucleated cells.
• Class II - on surface of activated APCs.

Question 16

How do B-Lymphocytes differentiate and secrete Ig?

Answer 16

• Naive B-cells randomly express clonal antibody receptors - initially IgD or IgM.

• Activated B-cells differentiate into efficent antibody secreting plasma cells, through the processes of affinity maturation and class-switching.
- These secrete high affinity IgG, IgA or IgE.

Question 17

What cell type is required for full activation of B-cells?

Answer 17

A T-helper cell.

Question 18

What are the three mechanisms that help antigen presentation, that only compotent APCs provide?

Answer 18

• MHC + peptide.
• Co-stimulatory surface molecules.
• T-cell activating cytokines such as (IL-12)

Question 19

Through which process do T-helper cells aid in producing high-affinity antibody? How does it work?

Answer 19

Linked-recognition.

• B-cells presents antigen to effector T-cell.
• Th-2 cell produces cytokines (IL-4,IL-2)
• Th-2 cell provides co-stimulation.

Question 20

Where do activated B-cells go to differentiate?

Answer 20

They migrate to the local follicle and differentiate in the germinal centre.

Question 21

What occurs during affinity maturation?

Answer 21

Random mutations in the variable region of the antibody, these affect the ability to bind antigen (affinity), those with low affinity do not survive.

Question 22

What occurs during class-switching?

Answer 22

This is the recombination of Ig gene segments, i.e. IgM into IgG. This produces an antibody with high-specificity.