Transplantation Flashcards
What proportion of the world population has kidney disease?
11%
35
What is the half-life for an adult kidney transplant?
Somewhere between 9 and 12 years. After this can go back on the waiting list.
How can we improve transplant outcomes?
What is the immune response to transplanted graft?
o Phases:
Phase 1: recognition of foreign antigens
Phase 2: activation of antigen-specific lymphocytes
Phase 3: effector phase of graft rejection
What features dictate immunology of transplantation?
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
What is HLA? What are the main classes?
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
How do we look at polymorphisms in MHC and HLA
A, B, DR and DQ - highly immunogenic
How we choose epitopes
How do we look at mismatches in clinic for HLA?£
The more mismatches, the worse the outcome.
What are the matches like in family members
- Parent → child = ≥3 always matched
- Sibling → sibling = 25% 6MM, 50% 3MM, 25% 0MM
Summarise T cell mediated rejection
Describe phase 1 of T cell mediated rejection
- 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
Describe phase 2 T cell activation
Describe phase 3 (effector phase) in T cell mediated rejection
- 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
- Cytotoxic T cells:
- 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
Describe the image
T cell mediated rejection
Structure surrounded by dark membrane - inflammatory cells within → tubulitis and interstitial inflammation in graft rejection
Describe the image
Endothelial cell layer with monocytes and macrophages.
Lots of inflammatory cells
Summarise Antibody mediated rejection
- 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)
Describe phases 1 and 2 of antibody mediated rejection. How is it similar to antibody action in infection?
- 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
Describe phase 3 of antibody-mediated rejection (intravascular)
-
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
What is this?
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
What dictates antibody-mediated rejection?
What is the relevance of ABO blood groups?
These antibodies circulate around and fix on the graft.
Describe screening for anti-HLA antibodies.
-
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)
