Adaptive Immune System

Question 1

What is the adaptive immune system

Answer 1

Specific to pathogen
- Ab receptor combines with a specific antigen
Delayed if new pathogen
Immunological memory
Antibody (humeral) mediated - B lymphocyte
Cell mediated
- T lymphocyte CD4 + CD8

Lymphocytes circulate in blood looking for pathogen that matches their TCR or Ab which is BCR

Question 2

Where do T cells mature

Answer 2

Thymus

Question 3

Where do B cells mature

Answer 3

Bone marrow + LN

Question 4

What happens to T cell in thymus

Answer 4

Develop CD markers and TCR
CD4 = T helper
CD8 = cytotoxic
NK cells

Question 5

What happens to B cells as they mature

Answer 5

Become either
Plasma cell and produce Ab - which is a BCR
Memory B cell

Question 6

What happens when B and T cells are matured

Answer 6

Migrate to secondary lymphoid organs where they encounter antigen and become activated

Question 7

What does CD4 TCR recognise

Answer 7

MHC II

Question 8

What does CD8 TCR recognise

Answer 8

MHC I

Question 9

What does MHC II present / react too

Answer 9

Extracellular pathogens

MO / dendritic cells endocytose and present MHC II to CD4 to initiate immune response (activates CD4)

Question 10

What does MHC I present / react

Answer 10

On all nucleated cells + platelet

Present intracellular pathogens e.g. virus / cancer

Question 11

What is central tolerance

Answer 11

Inactivation of cells that are bad 
Occurs in thymus and bone marrow
If self reacting BCR = destroyed 
If T cells recognise MHC = +Ve selection
If T cells rect too strongly with self antigen = -ve selection

Question 12

What is peripheral tolerance

Answer 12

Monitoring of lymphocytes within secondary lymphoid organs and circulation
Regulatory T cells destroy self-reactive lymphocytes - CD4 + CD8
Prevent overactivity and suppress immune response

Question 13

What do cytotoxic T cells do (CD8) when activated (when APC presents MHC1)

Answer 13

Release IFN-Y and TNFa - direct anti-viral and anti-tumour
Release cytotoxic granules (perforin and granzyme) similar to NK
Apoptosis by Fas
Programmed cell death
Complement activation
Recruit B cells

Question 14

How do they work

Answer 14

Host cell expressing MHC1 which shows virus

Recognised by TCR on T cell

Question 15

What do T helper cells do (CD4)

Answer 15

When CD4 activated differentiate into different T helper cells which release different cytokines
Release cytokines to help other immune
Promote B cell Ab class switching - IgM to IgG
Maxomise phagocyte activity by activating macrophages
Activate CD8 T cells

Question 16

What is role of Th1

Answer 16

Respond to intracellular pathogen
Maximise MO and CD8
Release IFN-Y
Stimulate B cells to produce IgG
Activate CD8 
Inhibit Th2

Question 17

What is role of Th2

Answer 17

Respond to extracellulair pathogens
Release IL
Activate mast cell, basophil and eosinophil
Stimulate B cells to produce all Ab but particularly IgE
Class switch to IgE
Inhibit Th1

Question 18

What is role of Th17

Answer 18

Respond extracellular
Pro-inflammatory
Recruit neutrophil and MO via CXCL-8

Question 19

What does overactivity of Th1 lead too

Answer 19

Type IV hypersensitivity

Question 20

What does overactivity of Th2 lead too

Answer 20

Type 1 hypersensitivity e.g. asthma

Question 21

What does overactivity of TH17 lead too

Answer 21

Pro-inflammatory state in autoimmune e.g. RA

Question 22

What does humeral immune system involve

Answer 22

B cells + Ab

Question 23

What is an antibody / Immunoglobulin

Answer 23

Glycoprotein produced by plasma cells of B lymphocyte that bind to antigen with high degree of specificity

Question 24

What makes up antibody

Answer 24

2 Heavy chain (Fc region)

2 Light chain (FAB region)

Question 25

What does FAB region do

Answer 25

Binds to antigen receptors Can be kappa or lamba Variable to bind to different. types Every single clone of B cell should have different variable region

Question 26

What does Fc region do

Answer 26

Binds to immune cells to activate | Constant region and determines type of Ab - IgG / IgM etc which all have different roles

Question 27

Role of IgM

Answer 27

``` Primary response Best at activating complement Cold Ab often IgM = haemolysis Produced as fetus Don't pass to foetal circulation so can cause haeomylsis ```

Question 28

Role of IgG

Answer 28

``` Secondary response Don't produce till born so crosses placenta Enhance phagocytosis Fixes complement Most abundant in serum ```

Question 29

Role of IgA

Answer 29

Present in secretions Most predominant in breast milk + other tracts Localised protection on mucous membrane Not produced till 1-2 months

Question 30

Role of IgE

Answer 30

Parasitic infection + allergy Mediates type 1 hypersensitivity Bind to Fc receptors on mast cell and basophil Least abundant

Question 31

Role of IgG

Answer 31

Unknown

Question 32

What occurs in Ab mediated immunity

Answer 32

Foreign antigen Lag phase whilst activate B cell differentiate into plasma Rely on innate Low volume of IgM Ab released Memory B cells also produced to remember antigen If encountered again memory B cells quickly produce plasma cells = release of high volume of IgM and IgG

Question 33

What is class switching

Answer 33

IgM - IgG | Requires stimulation by CD4 T cell

Question 34

How are B cells activated

Answer 34

B cell recognise antigen direct via BCR (Ab) Naive B cell and BCR (Ab) comes into contact with antigen Each B cell only has one Ab specific to one antigen B cell process antigen and present it with MHC II MHC II binds to T helper in secondary lymphoid Activates B cell Can also be activated directly by antigens without T cell Once activated develop into plasma cell or memory B cell (occurs in germinal centre of LN, spleen and MALT)

Question 35

What are functions of Ab

Answer 35

``` Immune complex Opsonisation Activating complement by classic pathway Agglutination by directly attaching ADCC ```

Question 36

What is ADCC

Answer 36

Ab dependent cellular cytotoxicity | Ab binds to target cells + initiates non-phagocytic cell mediated destruction e.g. by NK cell or granulocytes

Question 37

When does immune system vary

Answer 37

Neonates Elderly Pregnancy

Question 38

What affects elderly

Answer 38

Fewer T cells so dependent on memory Thyic involution Reduced B cell develpment More dependent on innate

Question 39

Main action of Ab

Answer 39

``` Agglutination Neutralisation Oppsonisation Complement activation Degranulation Cell mediated cytotoxicity ```

Question 40

What happens in passive immunity

Answer 40

Administration of pre-form Ab if exposed to high risk | No long term

Question 41

Where do you get it

Answer 41

Pooled from human donor in blood transfusion

Question 42

What happens in active

Answer 42

``` Administer pathogen or component Taken up by ABC Present on MHC II to T cell Activates B cell Long term immunity ```