Lymphocytes

Question 1

Why do we need adaptive immunity?

Answer 1

Only evolved recently

Protects us from repeat infections

Absence of it results in an inability to clear infections

Not without costs- autoimmunity

Question 2

What does the adaptive immune system do?

Answer 2

Improves efficacy of the innate immune response

Focuses the response on the organism responsible and at the site of infection

Had a memory

Needs tome to develop

Question 3

What is the characteristic of the memory response (secondary)?

Answer 3

More rapid

Heightened immune response

Therefore a severity on re exposure

Basis of vaccines

The memory is incredibly long lived

Question 4

What are the two parts of the adaptive immune response?

Answer 4

T cells: cell mediated. Produces cytokines (CD4) kills infected cells (CD8)

B cells: humoral. Produce antibodies

Question 5

How do T and B cells recognise pathogens?

Answer 5

BCR - B cell receptor

TCR

Question 6

What is an epitope?

Answer 6

The region of an antigen which the receptor binds to

Question 7

What part of an epitope do B and T cells recognise?

Answer 7

T cells: Linear epitopes in the context of MHC (primary structure)

B cells: recognise structural epitopes (the tertiary structure)

Question 8

How specific is the adaptive immune response?

Answer 8

Very

Each antibody only recognises one antigen

Question 9

What is clonal expansion?

Answer 9

Interaction between a foreign molecule and a unique receptor leads to the activation of the cell and causes it to undergo clonal expansion

This forms multiple copies of the same cell

Each of the clones express the same receptor

Question 10

How is the diversity of lymphocyte repertoire generated?

Answer 10

Each BCR chain receptor is encoded by separate multi gene families on different chromosomes

During B cell maturation these gene segments are rearranged and brought together

This is called
Immunoglobulin gene rearrangement

Question 11

What is the T cell receptor?

Answer 11

Part of a complex of proteins on the cell surface

The variable region is made by gene Reassortment

Recognised antigen fragments presented by other cells in the context of MHC

They are semi similar to antibodies, as they are coded fro by the same family of genes

Question 12

What is the MHC?

Answer 12

Major histocompatibilty complex

Plays a central role in defining self and non self

Presents antigens to T cells

Critical in surgery and donor matching

Question 13

What are the two families of MHC molecules

Answer 13

MHC class I:
Present on all nucleated cells (at various levels)

Has a single variable alpha chain plus a common beta microglobulin

MHC class II:
Normally only present on professional antigen presenting cells

Has and alpha and a beta chain

Question 14

How does MHC gene expression work?

Answer 14

Encoded by HLA genes

Polygenic: 3 class I loci and 3 class II loci

Expression is co dominant (maternal and paternal genes both expressed)

Therefore a person can have up to 6 of each gene

There are more than 17000 variants of the genes

Question 15

How do MHC complexes and T cell receptors interact?

Answer 15

MHCI:

Intracellular pathogens/antigens

Processed in the cytosol

Presented to CD8 (cytotoxic) cells

MHCII:

Extra cellular pathogens/antigens

Processed in endosomes

Presented to CD4 (helper) cells

Question 16

What is the role of T helper cells?

Answer 16

Produce cytokines (a family of inflammatory mediators)

Cytokines have a wide range of actions over a wide range of cells. They influence the outcomes of the immune response

Question 17

What are the classes of t helper cells?

Answer 17

Th1: pro inflammatory, boost cellular immune response

Th2: pro allergic

Th0: anti inflammatory
Limit the immune response

Th17: pro inflammatory
Control bacterial and fungal infection

Tfh: pro antibody

Question 18

What do Cytotoxic T cells do?

Answer 18

Kill their targets by apoptosis
(Characterised by fragmentation of nuclear DNA)

T killer cells contain perforin, granzymes and granulysin in granules that are released after they reach their target site

Perforin forms pores in the membrane of the pathogen and the granzymes are released triggering a cascade that leads to apoptosis

Question 19

What is the main purpose of a B cell?

Answer 19

To make antibodies?

Question 20

What is the structure of an antibody?

Answer 20

Made up of two light chains and two heavy chains

Had a variable and a constant region

They have a huge potential for diversity in the variable region

Question 21

What are the main functions of antibodies?

Answer 21

Neutralisation - an antibody binds to an active site in a virus or bacteria, thereby stopping the pathogen from doing its job

Opsonisation - the antibody makes the pathogen more attracted to being phagocytosed

Complement activation - esentially leads to the death of anything the antibody is bound to

Question 22

What are the 5 classes of antobodies?

Answer 22

IgG - Highest opsonisation and neutralisation activity

IgM - the pentamer that looks like a snowflake

IgA - expresses on mucosal tissues

IgD

IgE - involved one allergy

Question 23

What is the relationship between the BCR and the antibody?

Answer 23

The shape of the antibody is identical to that of the BCR the pathogen binds to

Question 24

How do B and T cells differ in binding antigen?

Answer 24

B cells bind to soluble antigen

Whereas T cells need to bind to antigens associated with MHC

Question 25

How is antibody production regulated?

Answer 25

Can’t be activated solely by antigen

Requires accessory signals either directly from microbial constituents or from a T helper cell

Question 26

What are the two pathways through which Antibody production is achieved?

Answer 26

Thymus dependant:
T helper cells
All Ig classes
Memory

Thymus independent:
Microbial constituents
Only IgM
No memory

Question 27

How does thymus independent signalling work?

Answer 27

Directly activated the B cells without T cells

Can only be done by pathogens that have molecules with a long repeating structure (eg bacteria with long chains of poly saccharide)

The second signal required is provided by a microbial PAMP

Question 28

How does thymus dependant activation of B cells work?

Answer 28

Membrane bound BCR recognises antigen

Receptor bound antigen is internalised and degraded into peptides

Peptides associate with MHCII molecules and are expressed on the surface of B cells

This complex is recognised but CD4 t helper cells

The B cell is activated