Immunology - Adaptive Immune Response

Question 1

Components of Adaptive Immune System

Answer 1

B cells, antibodies

T cells

Question 2

Recognising Pathogens

Answer 2

Antigen/Antigen receptors

response is unique to each antigen

Question 3

Antigens

Answer 3

Any substance which can cause an adaptive immune response by stimulating B ells and T cells

Question 4

PAMPs vs Antigens

Answer 4

PAMPs = 
Non specific 
Limited number of PAMPs common to many pathogens 
Small number of PRRs
Antigens = 
Specific 
Millions of different antigens 
Individual T cells and B cells only express one specific antigen receptor, which binds to one specific antigen

Question 5

T Cell Antigen Receptor

Answer 5

Membrane bound protein heterodimer

Alpha and Beta chains

Question 6

B Cell Antigen Receptor

Answer 6

Membrane bound antibody (IgM or IgD)

Light chain and heavy chain

Question 7

Antibody Composition

Answer 7

Heavy and light chains each contain a variable ad constant region
Variable region forms antigen binding site
Heavy chain constant region defines type of antibody

Question 8

Antibody Segmentation

Answer 8

Heavy and light chain proteins are encoded for by segmented genes
Random rearrangement of these gene segments occurs in individual B cells as they develop
This allows us to have many antibodies without using up a lot of DNA

Question 9

How do Antigens enter a Lymph Node?

Answer 9

Antigens released by phagocytes
TNFa stimulate immature tissue resident dendritic cells - B7 expression
Dendritic cells phagocytose antigens
Dendritic cells digest antigens and display small peptides on surface in complex with MHC
Pathogen derived particles, antigens and mature dendritic cells travel to local draining lymph nodes

Question 10

B Cell Activation

Answer 10

Opsonised antigen trapped by stromal cell
B cell binds to antigen, but needs a 2nd signal to activate
Antigen is protein = 2nd signal comes from T cell
Antigen is not a protein = 2nd signal from PRR+PAMP interaction on same antigen
Antigen is nuclei etc. = No 2nd signal needed, but must have multiple B cells binded

Question 11

T Cell Activation

Answer 11

Only recognise peptide antigens presented by MHC

Needs two signals

Question 12

Classes of MHC Proteins

Answer 12

Class I =
Expressed on all nucleated cells
Present peptide antigens to cytotoxic T cells
Class II =
Expressed only on professional antigen presenting cells (dendritic cells, macrophages, B cells)
Present peptide antigen to helper T cells

Question 13

Clonal Expansion

Answer 13

Only antigen specific T cells and B cells will divide

Once there are enough, differentiation will occur

Question 14

B Cell Differentiation

Answer 14

After clonal expansion, differentiate to plasma cells (effector B cells)
Produce antibodies
Non-protein antigens become low affinity, antigen specific antibodies
Peptide antigens (that used T cell help) become high affinity, antigen specific antibodies with memory cells
All are originally IgM, but high affinity antibodies differentiate further

Question 15

Five Different Secreted Antibody Types

Answer 15

IgM
IgG 
IgA
IgD
IgE

Question 16

IgM

Answer 16

Surface bound monomer = BCR

First type produced during an immune reaction

Question 17

IgG

Answer 17

Most abundant Ig in plasma
Actively transports across placenta
4 subtypes

Question 18

IgA

Answer 18

Second most abundant Ig type
Monomeric form in blood
Dimeric form in breast milk, saliva, tears, mucosal secretions

Question 19

IgD

Answer 19

Extremely low levels in blood

Surface bound = BCR

Question 20

IgE

Answer 20

Extremely low levels normally

Produced in response to parasitic infection and allergic responses

Question 21

Dual Biological Functions of Antibodies

Answer 21

Recognition Function

Effector Function

Question 22

Recognition Function of Antibodies

Answer 22

Binding to antigen mediated by variable region sites
Prevent viruses from infecting host cells
Prevent microbial toxins from disrupting normal cell function

Question 23

Effector Function of Antibodies

Answer 23

Clearance mechanisms mediated interaction of the content region with effector molecules 
Activate classical complement pathway
Act as opsonins 
Help stimulate NK cells
Can trigger allergic responses

Question 24

Helper T Cells

Effector Th Cells

Answer 24

Come from CD4+ cells

Help to activate other immune cells

Question 25

Cytotoxic T Cells

Effector Tc Cells

Answer 25

Come from CD8+ cells
Kill infected cells
Kill cancer cells

Question 26

Effector Th Cells Helping Macrophages

Answer 26

Effector Th cells migrate from lymph node to infected/inflamed site
Th cells are reactivated by macrophages in an antigen specific manner
Th cells enhance macrophage killing activity and pro-inflammatory response due to expression of co-stimulatory molecules

Question 27

Effector Th Cells Helping B Cells

Answer 27

Effector Th cells help B cels respond to protein antigens by providing the 2nd signal

Stimulate the Germinal Centre Response =
 B cell proliferation
Antibody heavy chain switching
Generation of high affinity antibodies
Differentiation into plasma cells and memory B cells

Question 28

Cytotoxic T Cells Killing Infected Host Cells

Answer 28

Effector Tc cells exit lymph node and migrate to site of infection
They recognise and kill infected tissue cells in an antigen specific manner
Their bigger, and full of granules which are directed to target cells

Question 29

Which cells are responsible for Immunological Memory?

Answer 29

Memory Th cells
Memory Tc cells
Memory B cells
Long-lived plasma cells

Question 30

Secondary (Memory) Response

Answer 30

Mainly IgG
Smaller lag phase
More antibodies produced
Probably fight the infection before you know you have it