Lymphocytes

Question 1

Why do we need immune memory?

Answer 1

To fight infections on subsequent infection

Question 2

Why do we need adaptive immunity?

Answer 2

Gives memory and specificity to clear infection
Improves efficacy of innate immune response
Focuses a response in the sire of infection and the organism responsible

Question 3

What are the main features of adaptive immunity?

Answer 3

Has memory

Needs time to develop

Question 4

What is immune memory?

Answer 4

Consequence of clonal selection
Antigen-specific lymphocytes are the cellular basis
Characterised by more rapid and heightened immune reaction
Can confer life-long immunity
Basis for vaccine

Question 5

What are the two types of adaptive immune response?

Answer 5

Humoral (B-cell)
Cell mediated (T-cells)

Question 6

Define antigen

Answer 6

Molecules that act induce an adaptive immune response

Question 7

Define epitope

Answer 7

The region if an antigen which the receptor binds to

Question 8

What do T-cells recognise?

Answer 8

Linear epitopes in the context of MHC (Major histocompatibility complex)
e.i A chain of amino acids

Question 9

What to antibodies recognised?

Answer 9

Structural epitopes

Question 10

What is clonal selection?

Answer 10

Each lymphocyte bears a single unique receptor
Interaction between a foreign molecule and that receptor leads to activation of adaptive immune response
Differentiated effector cells of the lineage will bear the same receptor
Self-specific receptors are deleted

Question 11

What are the problems with antigen diversity?

Answer 11

Exposed to large no. of different microbes

Immune system must be able to respond to all

Question 12

How do we deal with antigen diversity?

Answer 12

Encode a massive repertoire

10^10 different antibody molecules can be encoded

Question 13

How is the enormous diversity generated?

Answer 13

Functional genes for antigen receptors do not exist until they are generated during lymphocyte development
Each BCR chain is encoded by separate multigenerational families on different chromosomes
Single gene that can recombine in several ways
“Immunoglobulin gene rearrangement”

Question 14

What are the two types of T-cell?

Answer 14

T-helper cells

Cytotoxic T cells

Question 15

What are the main features of the T-cell receptor?

Answer 15

Part of a complex of proteins on the cell surface
Variable region made by gene reassortment
Recognises antigen fragments presented by other cells

Question 16

What is the role of the Major histocompatibility complex?

Answer 16

Central role in defining self and non-self
Encoded by HLA genes in humans
Presents antigens to T-cells
Critical in surgery and donor matching

Question 17

What are the main features of Major histocompatibility complex gene expression?

Answer 17

Polygenic

Co-dominant

Question 18

What is MHC class I?

Answer 18

All nucleated cells, although at various levels, levels may be altered during infection or by cytokines

Question 19

What is MHC class II?

Answer 19

Normally only on ‘professional’ antigen presenting cells

May be regulated by cytokines

Question 20

How does MHC I acquire antigen?

Answer 20

Constantly presenting proteins made within the cell on the cell surface
Always shows what proteins are being made e.g. self/non-self/viral

Question 21

How does MHC II acquire antigen?

Answer 21

Specific antigen presenting cell e.g. dendritic
Circulate looking for infectious material
Engulf infectious material and present on MHC II molecule

Question 22

What T-cells do MHC I interact with?

Answer 22

CD8- Killer

Question 23

What T-cells do MHC II interact with?

Answer 23

CD4- Helper

Question 24

What to CD8 cells do?

Answer 24

Kill their targets by apoptosis

Fragmentation of nuclear DNA

Question 25

How does MHC recognition work?

Answer 25

Recognises non-self and kills it

Question 26

What do CD4 cells do?

Answer 26

Produce cytokines
Cytokines have diverse actions on a wide range of cells
Influence the outcomes of the immune response

Question 27

What do B-cells do?

Answer 27

Make antibodies
Recognise soluble antigens
Need help from other sources to produce antibody

Question 28

What are antibodies?

Answer 28

Very specific, functional molecule that recognises proteins/ pathogens?

Question 29

What are the 5 classes of antibody?

Answer 29

IgG
IgA
IgE
IgD
IgM

Question 30

What are the three core roles of antibodies?

Answer 30

Neutralisation
Opsonisation
Complement activation

Question 31

Where do B-cells come from??

Answer 31

Derived from stem cells in the bone marrow
Migrate into the circulation
Mature B-cells are specific for a particular antigen
Specificity resides in the BCR

Question 32

What are the main features of the BCR?

Answer 32

Surface bound antibody- encodes the antibody the cell will make
Have unique binding site, before the cell ever encounters the antigen
Thousands of identical BCR on the surface

Question 33

What help do B-cells need in antibody production?

Answer 33

Require an accessory signal from:
Microbial constituents (only IgM)
Helper T-cells

Question 34

How do thymus-independent antigens work?

Answer 34

Directly activate B-cells without T-cells
Often bacterial/polysaccharide (need to be repetitive structure)
The second signal is provided by the microbial constituent or by an accessory cell
Is not very effective

Question 35

How does the Thymus-dependent approach work?

Answer 35

Membrane bound BCR recognises the antigen
Receptor bounds antigen is internalised and degraded into peptides
Peptides associate with ‘self-molecules’ and is expressed at the cell surface
Complex recognised by matched CD4 T-helper cell
B-cell is activated