Immunology (Liz - Transplantation) Flashcards
How many different MHC class I and II haplotypes are there?
6 Class I molecules
12 Class II molecules
What is the advantage and disadvantage of having different MHC haplotypes?
Advantage: Good diversity for surviving plagues etc
Disadvantage: Matching a donor with a recipient in transplant surgery
Most people are heterozygous for MHC at each locus, true or false?
True
- 2 MHC haplotypes on each cell
Why do people express 2 different MHC haplotypes?
Alleles from mother and father are coexpressed
- Co-dominant relationship
Due to MHC coexpression, how many possible haplotype combinations are there in mating?
4
e.g
Mum: Red and blue
Dad: Yellow and green
Offspring can be: Blue and green Blue and yellow Red and green Red and yellow
What are the 4 types of graft?
Autograft: skin from one place moved to another
Isograft: graft between genetically identical individuals
Allograft: between 2 individuals of the same species
Xenograft: between different species
Which grafts are usually accepted and not accepted?
Auto and isografts usually excepted
Allo and xenografts usually not accepted
What are the 4 laws of transplantation?
1) A to A = accepted
2) B to A = rejected
3) B to AB = accepted
4) AB to B = rejected
What are the 2 types of allogeneic rejection?
1) First set (new response)
2) Second set (due to memory T cells)
As a result of a T cell mediated anti-graft response
Describe the process of graft acceptance, first set rejection and second set rejection
Acceptance:
1) Grafted epidermis
2) Day 3-7 - revascularisation
3) Day 7-10 - Healing
4) Day 12-14 - Resolution
First set rejection:
1) Grafted epidermis
2) Day 3-7 - revascularisation
3) Day 7-10 - cellular infiltration
4) Day 10-14 - thrombosis and necrosis
Second set rejection:
1) Grafted epidermis
2) Day 3-4 - cellular infiltration
3) Day 5-6 - thrombosis and necrosis
Describe the direct and indirect recognition of alloantigens in grafted organs
Direct:
- Recognition (by recipient helper and cutotoxic T cells) of donor graft antigens (peptide and foreign MHC) directly on the surface of the donor APCs that migrate from graft to local lymph nodes
- Activated T cell migrate and destroy the graft via cell mediated cytotoxicity
Indirect:
- Recognition of processed and presented donor antigenic peptides on the recipients own APCs
How does a T cell response to a foreign antigen on a FOREIGN MHC?
- Known as allorecognition
- Non-self MHC similar enough to self MHC leading to a cross reaction giving a T cell response
What innate and adaptive immune cells are involved in acute graft rejection?
Innate:
NK cells and polymorph leucocytes
Adaptive:
B cells and CD8+ cytotoxic T cells
What are the roles of NK cells in graft rejection?
- Produces IFN-gamma that upregulates MHC class I and II expression on endothelial cells, so alloreactive T cell recognition is easier
- NK cells infiltrating transplant tissue produce cytokines that attract inflammatory leukocytes to transplant site
Which 3 graft types show the best survivial?
Kidney, heart and cornea
What type of therapy needs to be administered along side any allograft other than cornea transplants?
Immunosuppressive therapy
How is HLA tissue typing performed?
- White blood cells from donor and recipient added to seperate wells of microtitre plate
- If HLA-A allele 2 is present, antibodiy will bind to cell
- Addition of complement that binds to antibody will make pores in the cell
- Addition of dye - will be taken up by cells with pores - evaluation by microscopy
Why do the results of HLA tissue typing have multiple different wells for each donor?
Because lymphocytes express numerous HLA antigens - therefore testing is done with numerous antibodies specific for each antigen
Describe the effect of MHC class I and II matching on graft survival
- Mismatching of MHC class II is more severe than mismatching of MHC class I (HLA-A or B)
- Mismatching of both greatly accelerates rejection
How does the Luminex cross-matching assay work?
1) Microbeads with impregnated flurochromes of different intensites used
2) Each bead carries a different HLA allele
3) Beads with allele mixed with patients serum to see if they have pre-existing antibodies to the allele
4) Anti-HLA antibodies will bind to beads
5) A second phycoerythrin (PE) anti-human IgG antibody is added which will bind to primary antibody
6) Beads passed through machine that works like a flow cytometer
7) Based through laser that excites both fluorescently labelled secondary antibody and flurochrome allowing detection and identification of antibody
What can occur if the recipient has existing antibodies against the donor antigen?
Hyperacute graft rejection
- antibodies immediately bind to vascular endothelium of graft, causing complement and clotting factors to activate
- Complement split products attract neutrophils that release lytic enzymes
- platelets form and cause vascular blockage
- Thrombosis and necrosis of graft
Describe how chronic rejection of an organ can occur
1) Binding of anti-HLA antibodies to blood vessels of transplanted organs
2) This recruits monocytes and neutrophils bearing Fc receptors which leads to ADCC (antibody dependant cytotoxicity)
3) Accumulating damage leads to chronic inflammation and vasoconstriction
4) Over time vessels become obstructed, ischemic and fibrotic
What are privileged sites? Give some examples
Areas that a graft can be accepted without rejection because they do not have lymphatic vessels and sometimes no blood vessels
- Therefore no immune cells can reach to attack foreign antigens
e.g cornea, uterus, testes, brain
Give a very common example of an allograft that is not rejected
The foetus!!!
Carries MHC from mum and dad
An example of AB to A but is accepted not rejected!
Describe the stages and components of the immune system that lead to damage of a foreign transplanted organ
- APCs activate T helper cells
- T helper cells release cytokines:
> IL-2 and IFN-gamma required for cytotoxic T cell activation
> IL-2,4 and 5 involved in B cell activation which secrete antibodies
> Lymphotoxin and IFN-gamma together activate macrophages
- Complement activated via classical pathway after binding to antibody/antigen complexes within grafted organ
(See diagram, slide 35 of transplant lectures)
Name some current and potential future immunotherapies for reducing rejection
Current: Drug triple therapy
- Azothioprine (mitotic inhibitor, inhibits lymphocyte proliferation)
- Prednisolone (anti-imflammatory)
- Cyclosporin ( Inhibits IL-2 and IL-2 gene transcription)
Potential future:
- Antibodies to CD3, 40 and 25
- Soluble IL-1 receptors
- IL-2 analogs
- Antibodies to IL-2R
What is ICOS?
Inducible T cell stimulator (CD28 superfamily)
How is ICOS targeted in a new potential therapy to prolong grafts?
Anti-ICOS antibodies
- suppress T cell activation within a graft
- When combined with cyclosporin A, graft remained permanently unaffected in an animal model
- suggests that is prevents both acute and chronic rejection
How do anti-IL-2R antibodies work to increase graft survival?
Monoclonal antibody binds to IL-2R and prevents IL-2 binding
- Binding on T helper cells suppresses their proliferation
- Binding on CD8 T cells prevents their activation
How do IL-2 analogues work to increase graft survival?
Bind in place of IL-2 to IL-2R
- Less IL-2 binds
- Works the same as anti-IL-2R antibodies
How can IL-2 analogues be altered to kill T helper cells?
Conjugated with a toxin
Graft rejection can be suppressed by blocking co-stimulation of T cells by binding what soluble ligand with B7?
CTLA-4lg
After kidney, what is the most common transplant?
Bone marrow transplant
What is a bone marrow transplant often used to treat?
Leukaemia and severe combined immunodeficiency disease
What is graft versus host disease (GvHD)?
A complication after recieving a graft in which immune cells in the transplanted tissue recognise the components of the host as foreign
Why does GvHD occur in bone marrow transplants?
- Mature donor T cells contaminate the preparation of the stem cells
- These recognise alloantigens present on host cells
What % of bone marrow transplant patients get GvHD?
50-70%
What is the result of GvHD?
Inflammatory disease, leading to cytokine production that affects the skin, GI tract and liver
- In severe cases, there is GI haemorrhage and liver failure
What can be done as an alternative to a bone marrow transplant?
Purging of tumour cells in the bone marrow by:
- monoclonal antibodies and complement
- antibody-toxin conjugates
or
- antibodies coupled with magnetic beads (interfere with mitosis)
