Immunology 5 Flashcards
Describe T cell activation and differentiation into cytotoxic T cells and T helper cells Describe B cell activation and differentiation into plasma cells Briefly describe the functions of different antibody classes Understand immunological memory Describe monoclonal and polyclonal antibodies, their production and applications
1
Q
What sort of tissue is included in Gut associated lymphoid tissue (GALT)?
(3 marks)
A
- Tonsils
- Peyer’s patchs
- Lymphoglandular complexes
2
Q
What is included in Bronchial associated lymphoid tissue (BALT)?
A
Bronchi of lung
3
Q
What happens after a dendritic cell phagocytosed a pathogen and presents its antigen?
(5 marks)
A
- Expresses receptors for chemokines made of lymph nodes
- Lymph node will attract a licsenced dendritic cellwhich is attracted to lymph node by chemokine signalling
- Dendritic cell with antigen meets naïve t cdell
- T cell recognises pathogen and either becomes cytotoxic t cell
- OR activates B cell which produces antibodies
4
Q
What happens after a dendritic cell phagocytoses a pethogen and presents it on its cell surface?
(5 marks)
A
- Expresses receptors for chemokines (made by lymph node)
- Attracts liscened dendritic cell which is attracted to lymph node
- Dendritic cell meets naive t cell which recognises pathogen
- Activates t cell to either become cytotoxic
- OR t cell will activate B cell which will produce antibodies
5
Q
Summarise how a cytoxic t cell is activated.
(8 marks)
A
- In paracrotex of lymph node naive CD8+ T cell recognises specific peptide antigen (via TCR) presented on antigen presenting cell MHC I molecule
- CD8 assists binding of TCR and MHC I and increases signalling 100-fold.
- B7 receptor on antigen presenting cell binds CD28 on naïve T cell and promotes survival of T cell.
- IL-2 expression is induced in T cell and secreted IL-2 binds IL-2 receptors on T cell surface.
- T cell proliferates and differentiates into a cytotoxic T cell.
- Cytotoxic T cell travels to the site of infection.
- Target cells infected with intracellular pathogen, present the same specific peptide antigen on MHC I molecules which is recognised by cytotoxic T cell.
- Cytotoxic T cell secretes perforin and granzyme and apoptosis is induced in target cell.
6
Q
Summarise the activation of a T helper cell
(6 marks)
A
- In paracrotex of lymph node naive CD4+ t cell recognises specific peptide antigen presented on MHC II molecule
- CD4 assists in binding TCR and MHC II increasing signalling
- B7 receptor on MHC II binds to CD28 on naive T cell - promoting survival of T cell
- Cytokine secretion by antigen presenting cell dictates differentiation of T cell
- T cell differentiates into one of the following:
TH1, TH2, TH17, TFH or Itreg
- TFH recognises specific peptide antigen on MHC II molecule of naive B cell and initiates B cell activation
7
Q
What are the two types of B cell activation?
(2 marks)
A
T cell dependent
T cell INdependent
8
Q
How does T cell independent activation happen?
(7 marks)
A
- Naive b cell comes across antigen on pathogen and differentiates into plasma cell
- Plasma cell can now secrete antibodies - kill pathogen, induce opsonisation
- No T cell receptor needed as particular pathogen has repeats of same epitope
- Lots of antibodies bind to surface of pathogen via epitope
- Epitope brings antibodies in cluster, cluster activates them
- Signals to cell to proliferate as recognised multiple copies of itself as real antigen
- Together with TLR - bind more common pathogen and leads to activation of b cell
- IgM made through this process
9
Q
How does T cell dependent activation take place?
(5 marks)
A
- B cells in naive state come into lymph node by cirulatory systems of bone marrow and sit in germinal centres
- T cells come from thymus and sit in paracortex
- Dendritic cell thats been at site of infection is phagocytosed and presenting an antigen
- This cell comes to lymph node by lymphatic vessels and activates t cell
- Pathogen that binds BCR and pathogen comes in from lymph node
10
Q
What happens in the germinal centres of the lymph node to create a somatic mutation?
(4 marks)
A
- In germinal centre of lymph node - naive B cell recognises pathogen with specific BCR and phagocytoses pathogen
- Pathogen antigen presented on MHC II to T cell
- B cell MHC II/ peptide complex is recognised by antigen-specific activated T cell - and so B cell survives
- T cell signals to B cell to proliferate and B cell becomes centroblast
- Centroblasts express AID (protein) and undergo somatic mutation of V region, which will either increase or decrease BCR (antibody) affinity for pathogen antigen
11
Q
What happens in B cell activation after the somatic hypermutation?
(5 marks)
A
- Proliferation will cease and the xentroblasts will enter the light zone
- BCR affinity will be tested by follicular dendriteswhich trap and display intact pathogen
- B cells with low affinity BCRs will no longer present MHC II/ peptides and will apoptose
- B cells with high affinity BCR’s willl present many MHC II/peptides and antigen specific TFH cells promote survival
- TFH cells induce cytokine specific heavy chain class switching
12
Q
What is IgM and what does it do?
(5 marks)
A
- Made in first T cell independent activation of B cells AND B cell activation
- Activates complement proteins to cleave themselves when bound to surface of a pathogen
- Found on surface of BCR
- Secreted in t cell independent activation a large pentameter
- Important for fighting blood infections
13
Q
What does IgG do?
(3 marks)
A
- Agglutination - neutralises toxins
- Opsonisation
- Released in tissues to fight infection
(most commonly found in serum)
14
Q
What does IgA do?
(3 marks)
A
- Secreted into mucus
- Not in contact with complement proteins
- In any secretions on surface of our tissue
15
Q
What does IgE do?
A
- Attactched to mast cells and activates them
- Degranulates and releases all of its histamines and heparin and cytokines which is used for inflammation
16
Q
What does IgD do?
A
Not known - all we know it is a BCR
17
Q
What is the first stage in the process of remembering infection?
(3 marks)
A
- Naive B cell has just met antigen and expresses BCR in IgM class which has a low affinity for antigen
- Binds to antigen and activated B cell undergoes somatic hypermutation whihc increases its affinity for the antibody
- T cell induces a switch in B cell antibody and now has higher affinity as it has gone through hypermutation
18
Q
What happens in immunological memory after the class switch?
(3 marks)
A
- Plasma cells secrete fast quantities of IgG antibody into fluid to fight infection
- Mass production of antibody but also proliferation
- Plasma cells reproduce cells and make clones so have loads of antibody
19
Q
What happens in the process of immunological memory after the plasma cells have mass produced antibodies?
(2 marks)
A
- Get a memory cell which has the same class as the switched B cell but a higher affinity than BCR IgG
- Memory cell however can’t secrete BCR - so BCR stays on surface of memory cell BCR with low porliferation
20
Q
What happens in the secondary immune response for immunological memory?
(5 marks)
A
- Reinfection by same pathogen
- Create many B cells with recognition of slihgtly different antigens on pathogen
- Highest affinity BCR antibody recruited first - most efficient at pahgocytosing pathogen (expresses more MHC II)
- Process much quicker - BCR IgG doesn’t need to class switch from IgM to IgG
- Produce more antibody with higher affinity and memory cell with higher affinity than before
21
Q
What happens in the antibodies in doses of a vaccination?
(6 marks)
A
- First immunisation cause T cell independent resopnse and b cells start to make IgM
- Slower T cell dependent activation - T cell induces clonal expansion, somatic hypermutaion and class switch
- Increasing IgG
- Second vaccination goes round IgG memory cell
- Get second round of somatic hypermutation and therefore increase in affintiy
- With more vaccinations just increase IgG affinity
22
Q
What are the differnt forms of antibody technology?
(3 marks)
A
- Polyclonal antiserum
- Monoclonal antibodies
- Antibody applications
23
Q
What does polyclonal antiserum production make?
(2 marks)
A
- Mixture of antibodes produced that recognise different epitopes on surface of antigen
- May be antibodies to any impurites injected with antigen
24
Q
What is the rationale for the production of monoclonal antibodies?
(2 marks)
A
- Specifically recognise one epitope on antigen
- Immortal source of antibodies
25
Q
What are some of the downsides to producing polyclonal antibodies?
(3 marks)
A
- Each antiserum is differnt
- Can only be produced in limited serums
- Impossible to sue same antisera in multiple experiments
26
Q
How are monoclonal antibodies produced?
(7 marks)
A
- Immunise mouse with antigen
- Collect B cells
- Fuse with myeloma cells creatign hybridoma cells
- Isolate individual cells to get individual clones - MONOCLONAL
- Test antibodies produced by cells for antigen binding
- Grow hybridoma cells in large quantities
- Freeze cells and get immortal source of antibody
