Transplant Flashcards
What are the three phases of the immune response transplanted graft?
- Phase 1: recognition of foreign antigens
- Phase 2: activation of antigen-specific lymphocytes
- Phase 3: effector phase of graft rejection
What are the most relevant protein variations in transplants?
ABO blood. group
HLA
Where is HLA coded fo?
Chromosome 6 on MHC
What are the two main immune components for rejection?
T cell mediated rejection
antibody (B cell) mediated rejection
What are the three types of HLA class I?
A, B, C
What are the three types of HLA class II?
DR, DQ, DP
What cells is HLA I presented on?
ALL cells
What cells in HLA II presented on?
APCs
Why has the high variability (polymorphism) evolved in HLA?
So that HLA molecules can present a wide variety off antigens
What are the three most polymorphic/immunogenetics class subtypes for HLA?
A, B, DR
Explain T cell mediated rejection broadly
- APC presents donor HLA to recepient HLA
- T cell activates > inflammatory cell recruitment
- Effector phase > organ damage
What are the 3 key signals required for T cell activation?
- APC - T cell receptor interaction
- Co-stimulatory signal
- Amplification > activation via cytokine production
What are the actions. of activated T cells?
Proliferation Produce cytokines Provide help to CD8 cells Provide help to antibody production Recruit phagocytic cells
Whose APCs work in rejection, the recipient or the donor’s?
BOTH
Because if you transplant in an organ, that organ will contain APCs from the donor
Where does APC- T cell interaction occur?
In the lymph nodes
Which two cell types are activated in the effector phase ?
Cytotoxic T cells > granzyme, perforin, Fas ligand
Macrophages > phagocytosis, release of proteolytic enzymes, cytokine and free radical production
What do T cells do / how do they interact with endothelium in the effector phase?
They tether, roll and arrest on endothelial surface
They then crawl through interstitial and start attacking the tubular epithelium
What are typical histological features of T cell mediated rejection?
Lymphocytic interstitial infiltration
ruptured tubular basement membrane
Tubulitis (inflame cells within the tubular endothelium)
What can a fail in kidney transplant function be due to?
Rejection Nephrotoxic drugs Viral infection (from immunosuppressioN) vascular disease lymphoma (viral)
Explain the two types of antibodies you need to be weary of in transplants?
Anti-A and Anti-B antibodies (naturally occurring)
Anti-HLA antibodies (form following exposure)
How do antibodies act in a transplant?
- Antibodies bind to HLA antigens on endothelium of blood vessel in transplanted organ
Antibodies then fix complement which assembles to form MAC > ENDOTHELIAL CELL LYSIS - Binding of complement also recruits monophages, NK, neutrophils
- Inflammatory cells within kidney capillaries (CAPILLARITIS) also cause endothelial injury
What is the end product of antibodies acting against a transplant?
GRAFT FIBROSIS
What are the two key ways we prevent graft rejection?
Tissue typing (AB/HLA typing) Immunosuppression
When do we screen for anti-HLA antibodies=?
BEFORE transplant AT time of transplant (once organ assigned ) AFTER transplant (repeat measurement to check for new antibody formation)
What three techniques can be used for anti-HLA antibody screening?
Cytotoxicity assay
Flow cytometry
Solid phase assay
What are key drug types given for immunosuppression in T cell mediated rejection?
Steroids Calcineurin inhibitors Cell cycle inhibitors TCR inhibitors Monoclonal antibodies
What are key drug types given for immunosuppression in B cell mediated rejection?
anti CD20 (rituximab) BAFF inhibitors (target cytokines that promote B cell activation and growth) Proteasome inhibitors (block antibody production by plasma cells) Complement inhibitors
What categories is the general immunosuppression treatment made up of?
Induction agent
Baseline immune suppression
treatment of episodes of acute rejection
What is given for baseline immune suppression
TRIAD:
- Calcineurin inhibitor
- cell cycle inhib ( mycofenolat mofetil OR azathioprine)
- steroids
How do you treat episodes of acute rejection?
Cellular: steroids, OKT3/ATG
Antibody-mediated: IVIG, plasma exchange, antiC5, antiCD20
Name some calcineurin inhibitors
tacrolismus
Ciclosporin
Name some cell cycle inhibitors
mycofenolate mofetil
azathioprine
Name some TCR inhibitors
OKT3
ATG (Anti-Thymocyte globulin)
What can you give for GvHD prophylaxis?
methotrexate/cyclosporin
How do you treat GvHD’
steroids
What are common viral associated malignancies?
HHV8
EBV