Lymphocytes

Question 1

Why do we need adaptive immunity?

Answer 1

Protect us from repeat infections with same pathogens

Question 2

What does the adaptive immunity do?

Answer 2

Improve the efficacy of the innate immune response

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

Has memory

Needs time to develop

Question 3

When does the immune system exhibit memory?

Answer 3

Once the immune system has recognised and responded to an antigen

Question 4

What cells are involved in the ‘cell-mediated’ response?

Answer 4

T cells

Question 5

What cells are involved in the ‘humoral’ response?

Answer 5

B cells

Question 6

What are the two roles of T cells?

Answer 6

Production of cytokines to help shape immune response —> CD4 (helper)

Kill infected cells —> CD8 (killer)

Question 7

What is the role of B cells?

Answer 7

Produce antibody

Question 8

How do T and B cells recognise pathogens?

Answer 8

T cell and B cells receptors that detect antigens

Question 9

What are epitopes?

Answer 9

Region of an antigen which the receptor binds to

Question 10

What type of epitope do T cells recognise?

Answer 10

Linear epitopes in context of MHC molecules
—> primary structure if antigen

Question 11

What type of epitope do B cells recognise?

Answer 11

Structural epitopes —> 3D structure of the antigen in space
—> tertiary structures of antigen

Question 12

What is clinal expansion?

Answer 12

Each lymphocyte bears single unique receptor
—> interaction between foreign molecule and receptors leads to activation and clonal expansion

Question 13

What is the problem of antigen diversity?

Answer 13

We need a massive repertoire of lymphocyte receptors to deal with antigen diversity

Question 14

How is the antigen receptor diversity solved?

Answer 14

Through genetic recombination

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

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

—> called Immunoglobulin gene rearrangement

Question 15

What is the Major Histocompastabilty complex?

Answer 15

Plays a central role in defining self and non self

Present antigens to T cells

Critical in surgery and donor matching

Question 16

What are the two types of MHCs?

Answer 16

MHC class I

MHC class II

Question 17

What are MHC I made of?

Answer 17

All nucleated cells —> although at various levels

Single variable alpha chain plus common microglobulin

Question 18

What are MHC II made of?

Answer 18

Normally only on professional APCs

Have 2 chains —> alpha and beta

Question 19

What is MHC encoded by?

Answer 19

HLA genes in humans

Polygenic —> 3 class I and 3 class II loci

Expression is codominant

Each person can have up to 6 of each gene if completely heterozygous

Question 20

How do MHC and TCR interact?

Answer 20

Present intracellular pathogens/antigens to:

MHC I to CD8 T cell TCRs

MHC II to CD4 T cell TCRs

Question 21

What are the two families of T cells?

Answer 21

CD4 helper T cell

CD8 killer T cell

Question 22

What do CD4 cells do?

Answer 22

Produce cytokines —> which have diverse actions on a wide range of cells + influence outcome of the immune response

Question 23

What do CD8 cells do?

Answer 23

Kill targets by programmed cell death (apoptosis)

CTL store perforin —> release after target recognition —> perforin molecules polymerise, from pores

Question 24

How do CD8 cells kill infected cells?

Answer 24

1. CD8 cell scans cells, looks for non-self MHC
2. Virus infects the cell and release its contents
3. Cell starts making viral proteins
4. Displays these as non-self MHC
5. CD8 cells detects non-self MHC and attacks
6. CD8 kills the virally infected cell

Question 25

What is the structure of antibodies?

Answer 25

2 heavy and 2 light chains
—> divided into 2 areas —> constant and variable region

Variable region has a huge potential for diversity

Question 26

What are the 3 main functions of antibodies?

Answer 26

Neutralisation

Opsonisation

Complement activation

Question 27

What happens during neutralisation?

Answer 27

Antibody binds to active site on virus/bacteria ad prevents them from functioning

Question 28

What happens during opsonisation?

Answer 28

Antibody makes a pathogen more attractive for phagocytosis

Question 29

What happens during complement activation?

Answer 29

Cascade of events driven by antibody which leads to death of the bound pathogen

Question 30

What are the 5 main antibody classes?

Answer 30

IgG —> highest opsonisation and neutralisation activities

IgM —> produced first upon antigen invasion, increases transiently

IgA —> expressed in mucosal tissue, forms dimmers after secretion

IgD

IgE —> allergy

Question 31

Where do B cells come from?

Answer 31

Derived from HSC in bone marrow

Migrated into circulation and into lymphoid tissues

Mature B cells are specific for particular antigen

Question 32

How is the activation of B cells regulated?

Answer 32

Naive B cells require accessory signal:
—> directly from microbial constituents (thymus independent)
—> from a T helper cell (thymus dependent)

Question 33

What is the thymus independent path?

Answer 33

Microbial constituents

• directly activate B cells w/out help of T cells

Makes only IgM and no memory

Question 34

What is the thymus dependent path?

Answer 34

T helper cells

1) The membrane bound BCR recognises antigen

2) The receptor-bound antigen is internalised and degraded into peptides

3) Peptides associate with ‘self’ molecules (MHC II) and is expressed at cell surface

4) This complex is recognised by matched CD4 T helper cell (that has been activated by recognising an antigen presented via MHC II by an APC like a dendritic cell)

5) B cell activated by co-stimulation markers and cytokines that Tfh release

• all Ig classes and memory