Transplantation

Question 1

What proportion of the world population has kidney disease?

Answer 1

11%

Question 2

Answer 2

35

Question 3

What is the half-life for an adult kidney transplant?

Answer 3

Somewhere between 9 and 12 years. After this can go back on the waiting list.

Question 4

How can we improve transplant outcomes?

Answer 4

Question 5

What is the immune response to transplanted graft?

Answer 5

o Phases:
Phase 1: recognition of foreign antigens
Phase 2: activation of antigen-specific lymphocytes
Phase 3: effector phase of graft rejection

Question 6

What features dictate immunology of transplantation?

Answer 6

o The most relevant protein variations in clinical transplantation are:
- ABO blood group
- HLA (on chromosome 6 by MHC; n.b. HLA can mean the proteins OR the genes)
- Other minor histocompatibility genes
o Two major forms/components of rejection:
- T cell-mediated rejection
- Antibody-mediated rejection

Question 7

What is HLA? What are the main classes?

Answer 7

Question 8

Answer 8

o Features:

• They are highly polymorphic with hundreds of alleles for each locus
• High degree of variability from the areas of protein lining the peptide-binding groove which allows us to present a wide variety of antigens in that peptide-binding groove to the cells of the immune system

Question 9

How do we look at polymorphisms in MHC and HLA

Answer 9

A, B, DR and DQ - highly immunogenic

How we choose epitopes

Question 10

How do we look at mismatches in clinic for HLA?£

Answer 10

The more mismatches, the worse the outcome.

Question 11

What are the matches like in family members

Answer 11

• Parent → child = ≥3 always matched
• Sibling → sibling = 25% 6MM, 50% 3MM, 25% 0MM

Question 12

Summarise T cell mediated rejection

Answer 12

Question 13

Describe phase 1 of T cell mediated rejection

Answer 13

• To activate alloreactive T cells, the T cells require:
  
  • Presentation of foreign HLA antigens in MHC by APCs (both DONOR and HOST APC cells are involved)
  • Co-stimulatory signals
  • These actions occur in the lymph nodes – APCs pick up antigens from donor MHC and activate T cells in nodes
  • This leads to effector phase of rejection → inflammation caused leads to graft dysfunction (i.e. raised creat)
  • A biopsy can serve to determine if rejection is occurring

Question 14

Describe phase 2 T cell activation

Answer 14

Question 15

Describe phase 3 (effector phase) in T cell mediated rejection

Answer 15

• Effects cells have inside the transplanted organ:
  
  • Cytotoxic T cells:
    
    • Granzyme B (toxin)
    • Perforin (punch holes)
    • Fas-ligand (apoptosis)
  • Macrophages:
    
    • Phagocytosis
    • Proteolytic enzymes
    • Cytokine release
    • O₂ and N₂ radicals
• Effector phase:
  
  • The T cells will tether, roll and arrest on the endothelial cell surface
  • They will then crawl through into the interstitium and start attacking the tubular epithelium

Question 16

Describe the image

Answer 16

T cell mediated rejection

Structure surrounded by dark membrane - inflammatory cells within → tubulitis and interstitial inflammation in graft rejection

Question 17

Describe the image

Answer 17

Endothelial cell layer with monocytes and macrophages.

Lots of inflammatory cells

Question 18

Summarise Antibody mediated rejection

Answer 18

• Phase 1: exposure to foreign antigen
• Phase 2: proliferation and maturation of B cells with antibody production
• Phase 3: effector phase – antibodies bind to graft endothelium (capillaries of glomerulus and around tubules)

Question 19

Describe phases 1 and 2 of antibody mediated rejection. How is it similar to antibody action in infection?

Answer 19

• Whilst anti-ABO blood group ABs naturally occur, anti-HLA antibodies are not naturally occurring
  
  • Can be pre-formed due to previous exposure to epitopes (e.g. previous transplantation, pregnancy, transfusion)
  • Can be post-formed (after transplantation)
• Action of Antibodies in Infection – the same mechanisms occur in transplant rejection:
  
  • Neutralise toxins
  • Opsonise (aid phagocytosis)
  • Antibody-dependant cellular cytotoxicity
  • Complement activation (which leads to):
    
    • MAC lysis
    • Opsonise (aid phagocytosis)
    • Inflammation

Question 20

Describe phase 3 of antibody-mediated rejection (intravascular)

Answer 20

• Phase 3 (antibodies in transplantation):
  
  • Antibodies bind to antigens (HLA) on the endothelium of the blood vessels in the transplanted organ
  • Antibodies fix/activate complement which assembles to:
    
    • Form MAC à endothelial cell lysis
    • Recruit inflammatory cells to the microcirculation
  • Antibodies can crosslink the MHC molecules, thus activating them
  • The antibodies can also directly recruit mononuclear cells, NK cells and neutrophils à capillaritis
• Cardinal feature of antibody-mediated rejection = capillaritis = inflammatory cells in capillaries of the kidney à injury
• The above processes → procoagulant tendencies and closure of the microcirculation leading to graft fibrosis

Question 21

What is this?

Answer 21

Antibody-mediated rejection

• Histology:
  
  • Inflammatory cell infiltrate
  • Capillaritis (inflammatory cells in the microcirculation – a cardinal feature of antibody mediated rejection)
  • Immunohistochemistry can see fixation of complement fragments on endothelial cell surfaces

Question 22

What dictates antibody-mediated rejection?

Answer 22

Question 23

What is the relevance of ABO blood groups?

Answer 23

These antibodies circulate around and fix on the graft.

Question 24

Describe screening for anti-HLA antibodies.

Answer 24

• HLA Typing – BEFORE TRANSPLANT – via PCR DNA sequencing:
  
  • Particularly important for BM and kidney transplantation
  • Less important in heart and lung transplants
• Screening for anti-HLA antibodies – BEFORE, AT TIME (at organ assignment) and AFTER TRANSPLANT – 3 assays used:
  
  • Cytotoxicity assays:
  • Flow cytometry:
  • Solid phase assays (uses a series of beads containing all the possible HLA epitopes):
    
    • Recipient’s serum is mixed with beads and fluorescently labelled immunoglobulin is used to determine which HLA epitopes the antibodies bind to (can also give an indication of the strength of the reaction)
    • Patients that have antibodies to lots of different types of antibodies are regarded as highly sensitised
• NOTE: mismatch positive transplantation CAN take place, but requires a lot of preparation (plasma exchange and IVIG)

Question 25

Describe Cytotoxicity assays.

Answer 25

• Inspects if recipient’s serum will kill the lymphocytes of the donor, in the presence of complement
• Positive crossmatch suggests that there is cell lysis (i.e. +ve is a bad thing)

Question 26

Describe flow cytometry.

Answer 26

• Inspects if recipient’s serum binds to the donor’s lymphocytes
• Detection of bound AB by fluorescently labelled anti-human immunoglobulin
• A broad test to look at whether antibodies bind antigen irrespective of whether they bind complement

Question 27

Describe solid phase assays.

Answer 27

• Solid phase assays (uses a series of beads containing all the possible HLA epitopes):
  
  • Recipient’s serum is mixed with beads and fluorescently labelled immunoglobulin is used to determine which HLA epitopes the antibodies bind to (can also give an indication of the strength of the reaction)
  • Patients that have antibodies to lots of different types of antibodies are regarded as highly sensitised

Question 28

How do combat antibody-mediated rejection?

Answer 28

Question 29

How do we present and treat graft rejections?

Answer 29

Question 30

What are consequences of transplants?

Answer 30

• Infection - reduce IS
• Vascular disease - control hypertension
• Post transplant lymphoproliferative disease - reduce IS drugs
• Recurrent glomerulonephritis - depends of GN

Question 31

Answer 31

HLA/ MHC

Question 32

Answer 32

option 3

Question 33

Answer 33

T cell mediated and monocyte and macrophage

Question 34

Answer 34

Steroids

Question 35

Answer 35

Hypertensive arteriosclerosis.