Adaptive Immune System

Question 1

What are the main products of the adaptive immune response?

What do both of these products rely on?

Answer 1

Antibodies
Cytotoxic TCs

Rely on TH cells

Question 2

Why are TCs able to detect multiple different antigens?

Answer 2

Each TC has a TcR with a variable domain that can alter its shape to enable different TCs to bind different antigens

Question 3

What is the function of the MHC?

What are the 2 classes and what are the features of each?

Answer 3

Presents antigens in form which TC can recognise
MHC 1:
-on almost all cells with nucleus
-present antigens from within cell i.e. virus
-recognised by CD8

MHC 2:

• dendritic cells, macrophages, monocytes + BC
• presents antigens from outside cell i.e. from antigen which has been phagocytosised and processed
• recognised by CD4, leading to activation

Question 4

How are TH cells formed?

What are the 2 forms of TH cells and what are their functions?

Answer 4

MHC2 presenting antigen activates CD4 cells which proliferate for a few days before differentiating into TH cells

TH1:

• stimulate B cells to produce IgG
• secrete IL-2= stimulates proliferation of CD4 + CD8
• aid CD8->cytotoxic TC
• associated with type IV hypersensitivity reaction by travelling to site of infection + releasing cytokines to recruite immune cells

TH2:

• stimulate B cells to produce all antibodies but IgE primarily
• travel to infection site + release cytokines to stimulate immune cell recruitment
• activates mast cells + eosinophils
• important in parasite infections + type 1 hypersensitivity reactions + asthma

Question 5

How are cytotoxic TC activated and what is their function?

Answer 5

Dendritic cells display antigenic material to CD8 cells via MHC1 stimulation proliferation + differentiation to cytotoxic TC

Destruction of cells invaded by pathogens due to antibodies and other cells no longer being affective against the pathogen once inside the cell
-infected cell will present MHC1 with same antigentic material specific to cytotoxic TC
Destroy infected cell via:
-granule exocytosis= enzymes causing cell lysis
-activation of Fas molecul to induce apoptosis

Question 6

What are the basic structural features of antibodies and what role do they have in their action?

Answer 6

• 2 heavy chains and 2 light chains
• Fc portion= binds to Fc receptors of the immune system + is constant between all antibodies
• Variable region to enable confirguration to specific antigens

Question 7

What are the 5 different classes of antibodies?

Answer 7

IgA
-secreted in mucous to protect mucous membranes

IgD
-found on B cell membranes but is unstable and doesn’t last long once secreted

IgE
-important in allergies and asthma
I.e. can be measured to indicate persons allergen status

IgG

• most common
• measured to detect patients immunity to condition or assess response to vaccine

IgM
-produced 1st in acute infection i.e. measuring gives indication of acute infection as disappears when infection does

Question 8

What is the role of BCs in immune response and how are they activated?
Where does BC differentiation occur?

Answer 8

Located in LN, spleen and MALT where they pick up antigens specific to their antibodies
Antigen process and present on MHC2
TH cell specific to antigen recognises and produces cytokines to activate BC

Question 9

Where does BC differentiation occur?

What does BC differentiation involve?

Answer 9

Differentiate into either plasma cell or memory cell and occurs in germinal centre of LN/spleen/MALT

Diff to plasma cell involves:

• affinity maturation i.e. increased specificity to antigen
• antibody class switch
• production of antibody

Diff to memory cells 
-affinity maturation and class switch BUT no production of antibodies

Question 10

What are the 6 main functions of antibodies in the immune system?

Answer 10

Form antibody-antigen complexes to activate classical pathway of complement

Attach + neutralise pathogens toxins

Bind to bacteria and virus receptors to prevent function of pathogens i.e. bacterial nutrition or viral invasion

Agglutination i.e. involves clumping of pathogens together to slow spread

Act as opsonins

Antibody-dependent cell-mediate cytotoxiciy (ADCC)
-antibodies attach to pathogens/abnormal cells to facilitate recognition by NK, neutrophils, macrophages or eosinophils to kill