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What is the MHC?

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.


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

Human leucocyte antigens. 

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


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

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.


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

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.


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

1) Primary antibody response - Small response, memory cells produced.

2) Secondary antibody response - Rapid and effective response.


What is the difference between a relative and absolute contraindication?

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


In which situations should an immunisation be deferred?

1) Acutely unwell with systemic symptoms or fever.

2) Evolving neurological condition.


Which conditions are not contraindicated for routine vaccination?

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


Should a child taking prednisolone be given a routine vaccination?

Depends on the vaccine.

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


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

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


What are the two main antigen-presenting cells?

Macrophages and dendritic cells.

They also secrete cytokines that stimulate the immune response.


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

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


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

CD4+, T-helper cells.


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

CD8+, T-killer cell.


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

• Class I - on all nucleated cells.

• Class II - on surface of activated APCs.


How do B-Lymphocytes differentiate and secrete Ig?

• 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.


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

A T-helper cell.


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

• MHC + peptide.

• Co-stimulatory surface molecules.

• T-cell activating cytokines such as (IL-12)


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


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


Where do activated B-cells go to differentiate?

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


What occurs during affinity maturation?

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


What occurs during class-switching?

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