Lecture 6: Transplant/Hypersensitivity Flashcards
Difference between allograft, autograft, syngeneic graft, and xenograft?
Allograft - another person, same species
Autograft - same person
Syngeneic - another person, identical genes
Xenograft - different species
What mediates rejection specifically?
Inflammatory reactions
What mediates graft rejection specifically?
Adaptive immune system due to specificity and memory
What does a graft need to be deemed as to be successful?
The body must recognize the graft as “self”
What molecules does a T cell recognize?
MHC/HLA
When does a transfusion reaction occur?
When a person receives blood with different antigens than their own.
What kind of antigens and antibodies do A blood types have?
A antigens on the surface, B antibodies produced.
What kind of antigens and antibodies do O blood types have?
No antigens on the surface, A and B antibodies produced.
If I mix anti-A and anti-B antibodies and have agglutination with both, what blood type did I mix?
AB
If I mix anti-A and anti-B antibodies and have agglutination with just my anti-A, what blood type am I?
A
If I have no agglutination, what blood type do I have?
O
Which Rh group is the only clinically significant one?
RhD
What does a person with Rh+ blood have?
They have the D antigen present on their RBCs.
What happens when an Rh- and an Rh+ person share blood for the first time?
The Rh- person will start making antibodies (IgG) to the D antigen.
What are the two ways I can trigger the production of IgG in terms of Rh blood groups?
Exposure via pregnancy or transfusion.
What are the major antigen targets of transplant rejection?
MHC/HLA
What is rejection of a transplant mainly due to?
T-cells
What is suppressive therapy?
Therapy to inhibit the immune responses that contribute to rejection.
What are the 3 forms of rejection?
Anti-body mediated (Hyperacute and acute)
Cell-mediated (acute)
Chronic rejection (chronic)
What are the common symptoms of rejection?
General discomfort, uneasiness, or ill feeling
FLS
Dependent on organs as well.
What symptom is common in a pancreatic transplant?
High blood sugar
What symptoms are common in a heart transplant?
SOB and reduced ability to exercise
What symptoms are common in a liver transplant?
Yellow skin color and easy bleeding
What symptoms are common in a kidney transplant?
Oliguria
What is the process of a hyperacute rejection?
Occurs when preformed anti-blood antigen or anti-HLA antibodies bind to vascular endothelial cells of a graft.
Complement is activated
Antibodies against HLA antigens are deposited into the tissue endothelium and vasculature.
Neutrophils, macrophages, and platelets are attracted to the site, causing further cellular damage.
Platelet deposition leads to vascular thrombosis.
When do I typically see hyperacute rejections?
ABO Blood Type Incompatibility
What are the two types of acute rejections?
T-cell mediated or antibody mediated
What is the most common type of rejection?
Acute T-cell mediated rejection
How fast does an acute rejection typically occur within?
1 week
Explain the two processes of a T-cell mediated rejection
APCs present donor alloantigens to host T lymphocytes.
If APCs are from the donor, it is direct activation.
If APCs are from the recipient, it is indirect activation
Explain the mechanism of CD8 cells in T cell mediated rejection
CD8 cells recognize MHC 1 molecules
CD8 differentiate into CTLs
CTLs directly kill graft tissue
Explain the mechanism of CD4 cells in T cell mediated rejection
CD4 recognize MHC 2 molecules
CD4 differentiate into Th cells.
Th cells secrete cytokines to influence other immune cells (B, CD8, macrophages, and NK cells)
What are the effects of cytokines that lead to graft injury?
Increased vascular permeability
Accumulation of immune cells to graft site
Activation of macrophages
Explain the process of antibody-mediated/humoral acute rejection
Occurs as a result of B-lymphocyte proliferation, followed by differentiation into plasma cells.
Plasma cells produce donor-specific antibodies (DSAs)
Previous exposure to a relevant HLA antigen causes rejection but high circulation of antibodies does not occur until after transplantation.
Complement-fixing antibodies are generated -> graft vasculature is targeted and rejection ensues.
Explain the process of chronic rejection
It is immune-mediated inflammatory injury that occurs over the span of years.
This results in residual circulating anti-graft T lymphs or antibodies that compromise graft integrity.
Leads to endothelial smooth muscle thickening and arterial occlusion
What are the characteristics of chronic rejection?
Fibrosis
Vascular injury/impaired blood supply
Loss of graft function
Why does fibrosis occur in chronic rejection?
T lymphocytes and macrophages produce cytokines which attract fibroblasts and infiltrate tissues.
When does GVHD typically occur after?
100 days following a transplant of allogeneic stem cells or bone marrow.
What three requirements must be met for GVHD to develop?
Graft must contain immunologically competent cells
Recipient cells must express antigens that are not present on donor cells
Recipient must be immunologically compromised and incapable of mounting an effective immune response
How often does GVHD occur even in matched HLA patients?
40% of the time
Explain the process of GVHD
Newly transplanted donor T cells react to the HLAs on host cells and attack the recipient’s body.
This is due to the donor T cells recognizing the recipient’s body as foreign.
What three organs systems are most commonly affected in GVHD?
GI tract: diarrhea, abdominal cramping, nausea, and anorexia. Sometimes GI bleeds
Skin: rashes, itching, blisters, and ulcerations (sometimes)
The rashes typically start on hands and feet.
Liver: jaundice, liver disease
What is the main target of immunosuppression?
Inhibit T cell activation and effector functions.
What are the three types of immunosuppressants we typically give for organ transplants?
Cytotoxic drugs
Specific immunosuppressive agents
Anti T cell antibodies
What is current immunosuppressive therapy successful in?
Preventing and reducing acute rejection and GVHD.
When does autoimmunity occur?
The body’s immune system cannot differentiate between self and nonself.
Against what does autoimmunity occur?
self antigens
How much of the US population do autoimmune disease typically affect?
5-8%
List at least 2 organ specific and non-organ specific autoimmune diseases.
Organ-specific: MS, Hashimoto’s, Myasthenia gravis, Addison’s disease, pernicious anemia, Type 1 DM
Non-organ specific: Scleroderma, SLE, RA
What are the two processes self-tolerance relies on?
Central tolerance and peripheral tolerance