Transplantation Flashcards
Define autograft, Syngeneic (isograft), allograft, and xenogeneic graft.
Autograft - self donation, 100% success rate without rejection
Syngeneic - from identical person, lack of rejection
Allograft - non-identical human donated graft, rejection in 10-13 days
Xenogeneic graft - diffferent species donation, rejected rapidly
What factors need to be considered during blood transfusions and what occurs if there is a mistake?
RBC antigen (A, B, or both)
Rh factor
Type II hypersensitivity reaction
What type of allograft transplant doesn’t need HLA assessment?
Cadaveric cornea
Anterior chamber of eye has immunosuppressant capabilities
Cornea is avascular, i.e. sequestration
What dictates donor selection in highly vascular organs?
ABO type
Is HLA matching required for liver transplants?
No
Hepatocytes express low levels of HLA type I/ no HLA type II markers, makes liver relatively anti-inflammatory
Chronic rejection deterred by cyclosporine and tacrolimus
What mediates a graft rejection response?
T cells
Good MHC matching just prolongs time before rejection, always still need immunosuppression
Why is organ transplant time sensitive?
Hypoxia after graft removal causes inflammation, increasing antigen presenstation
What generates graft vs. host disease?
Immunologic memory of donor T cells transferable to naive recipient
Lymphocytes in graft will respond to immunosuppressed recipient as a foreign antigen
What is the mechanism and time table for hyperacute rejection?
Minutes to hours
Due to preformed antibody against ABO or endothelial vessel wall
Complement activation via Type II hypersensitivity reaction
Test to prevent via cross matching
Hyperacute reaction prevents xenograft use
What is direct allorecognition?
Donor DC is still present in graft and presents antigen directly to recipient CD4 or CD8 cell
Mechanism of acute graft rejection
What is indirect allorecognition?
Graft antigen is endocytosed, processed, and presented via MHCII by patient’s APC to self CD4 T cell
Mechanism of chronic rejection when donor APCs are gone
Why can acute rejection occur up to 6 months post transplantation?
Type IV hypersensitivity response
Donor APC presents graft antigen to recipient T cell
Initiates mechanism of Type IV hypersensitivity
What is the time table and mechanism for chronic graft rejection?
> 2 months to years
Graft infiltration of CD$ T cell driven by indirect allorecognition
Formation of ectopic tertiary lymphoid organs within graft results in CD4-B cell interaction producing antibodies against graft
Damage results from vessel injury via complement deposition
Injured endothelial cells create growth factors causing myofibroblast proliferation with ECM deposition obstructing vessels
What is graft versus host disease?
Donor attacks the recipient
Donor T cells mediate an immune response in host tissue
How can GVHD be triggered even when the HLA is a 100% match?
Minor histocompatibility antigens can still trigger GVHD
E.g. Brother as donor to sister will cause GVHD due to male specific antigens
