Transplantation immunology week 3 Flashcards
define the following terms:
auto transplant
syngenic transplant
allograft
xenograft
autograft: from self. i.e. skin graft. Here the cells/tissue are transplanted within the same individual—– No Issues with Immune system; Good only for skin graft; And Autologous Bone marrow/Stem cell graft where the host tissue/cells are preserved before the administration of chemotherapy for treatment of cancer.
syngenic graft: Transplant Between Genetically Although between two individuals, these are genetically Identical and therefore should not have any differences Identical Twins
allograft: from non-identical individual of the same species
xenograft: from different species
When do hyperacute solid organ transplant rejections occur? What are they caused by?
Hyper-acute Rejection: The Recipient has high levels of circulating antibodies against the donor’s HLA (ONE OR MORE) — This could lead to complete failure of engraftment due to the alloantibody-antigen complex mediated complement activation cascade and happens in minutes and within 24 hrs of transplantation
[This does not happen now due to diligent monitoring of pre‐sensitization status of the solid organ transplant candidates by the Histocompatibility Testing Laboratory].
When does acute rejection occur? Explain the immune response in this type of rejection.
Is this treatable?
Acute rejection is the result of a cellular immune response that involves Monocytes/T Cells and cytokines. Naïve T cells recognize the donor antigens presented by the recipient’s APC (Antigen Presenting Cells) and become activated. This results in a cellular immune response orchestrated by CD4, CD8 T Cells, & Macrophages along with soluble mediators such as cytokines and chemokines. Acute rejection can occur within a few weeks to a few months after transplantation, and it can also occur after the first year of transplantation. In most cases it does not lead to graft loss. It is treatable when it is detected early during the initial few episodes, however, repeated episodes can lead to chronic rejection and graft loss.
What is the cause of chronic graft rejection? What is the immune response in chronic graft rejection? What is the timeline?
Chronic rejection: Years after transplant. “Slowly deteriorating graft function caused by fibrosis of the graft parenchyma and widespread arteriopathy are the hallmarks of chronic rejection that lead to loss of function and eventual graft loss” . This could be due to intractable repeated Cellular and Antibody mediated rejections and may even begin at the time of transplantation. It is a slow progressive process and the recipients may experience the same symptoms related to primary organ failure. Current evidence indicates that chronic rejection could result from both antibody and cell mediated assault. Also it could result from non-immune mediated events. In any case, chronic allograft rejection is the major problem in solid organ transplantation and 30% on renal transplant waitlist are due to chronic rejection of previous transplants.
