Lymphocytes

Question 1

What are the characteristics of lymphocytes?

Answer 1

Inability to clear infection without them
Protects from secondary infection due to memory
Focuses response to site and organ

Needs time to develop
Can result in auto-immunity

Question 2

What lymphocyte results in Cell-mediated response

What lymphocyte results in humoral response?

Answer 2

T cells - produce cytokines - CD4 helps and CD8 kills

B cells - produce antibodies

Question 3

How do t and B cells recognise pathogens?

Answer 3

TCR

BCR

Question 4

What is the Epitope?

Answer 4

The region of an antigen which the receptor binds to :
- antibodies recognise structural epitopes

• T cells recognise linear epitopes ( in the context of MHCs)
• The paratope is the area of the antibody which binds

Question 5

What is clonal expansion?

Answer 5

Unique receptor and foreign antigen interaction allows activation and expansion of the receptor cell

Differentiated effector cells of that lineage will have the same receptor

Question 6

How is antigen receptor diversity generated?

Answer 6

Recombination - Immunoglobulin gene rearrangement

Each BCR receptor chain ( Kappa, Lambda, heavy chain genes ) is encoded by separate multigene families on different chromosome

Question 7

Describe the structure of the T cell receptor?

Answer 7

Alpha and Beta region make up variable region

Cytoplasmic tails connected by disulphide bonds and go through transmembrane

Question 8

What are the differences between MHCI and MHCII?

Answer 8

MHC class I : found on all nucleated cells at various levels
MHC class II : found in 'professional' antigen presenting cells

MHC class I : has single variable alpha chain and common beta microglobulin added 
MHC class II : has 2 chains, alpha and beta

Question 9

How do genes control the MHC?

Answer 9

Encoded by HLA genes

Polygenic so 3 class I and II loci

Co-dominant expression

• so if a person was completely heterozygous they could have up to 6 of each gene

Question 10

What MHC - TCR interactions occur in the cytosol?

Answer 10

For intracellular antigens

The antigen is presented on the MHCI taken from the target cell it is attached to

Presented to CD8 T cells

Question 11

What MHC - TCR interaction occurs in endosomes?

Answer 11

CD4 binds to the beta2 domain of the MHC class II

For extracellular antigens

The antigen is presented on the MHCII
Presented to CD4 T cells

Question 12

What roles do CD4 T helper 1 cells play?

Answer 12

• Pro - inflammatory
• Boost cell immune response - viruses
• Tumour necrosis factor
• Interleukin 12

Question 13

What roles do CD4 T helper 2 cells play?

Answer 13

• Pro allergic
• Multicellular response - parasitic
• IL-4, IL-5, IL-13

Question 14

What roles do CD4 TH0 regulatory cells play?

Answer 14

• Anti inflammatory
• Limit immune response
• IL-10, TGFbeta

Question 15

What roles do CD4 T helper 17 play?

Answer 15

• Pro inflammatory
• Bacterial / fungal infection - in skin wounds not in the cells
• IL-17, IL-23, IL-6

Question 16

What roles do CD4 T follicular helper cells play?

Answer 16

• Pro antibody
• IL-21
  work with B cells to make better antibodies

Question 17

What do CD8 cytotoxic T lymphocytes do?

Answer 17

Kill through apoptosis when they notice non-self MHC

CTLs store perforin, granzymes, granulysin in granules

Question 18

How do antibodies work against bacteria?

Answer 18

Neutralisation - prevents bacterial adherence

Opsonisation - Promotes phagocytosis

Complement activation : enhances opsonisation and lyses some bacteria

Question 19

When is the BCR formed, before or after cell encounters antigen?

Answer 19

Before cell encounters antigens

* can bind to soluble antigen, doesn’t need a MHC

Question 20

What requires an accessory signal?

Answer 20

Naive B cells require accessory signals

Directly from microbial constituents
or
From t helper cells

Question 21

How is antibody production by B cells achieved?

what two methods

Answer 21

T helper
Thymus dependent
All Ig classes, has memory

or

Microbial constituents
Thymus independent
only IgM, no memory

Question 22

What antigens can activate B cells independently of the thymus?

Answer 22

Polysaccharide repetitive antigen structures

A second signal con be provided by microbial PAMP

Question 23

Describe thymus dependent antibody production?

Answer 23

Membrane bound BCR recognises antigen, B cell with internalise the antigen and present its peptides on a MHCII itself.

Separately, Dendritic cells also notice the antigen and present it to CD4 helper cells which become activated

Activated CD4 then notices the antigen on the MHCII on B cell, activates help pathway:

• cytokines and cell markers = activate B cells

= antibody production