Lecture 10: Transplants

Question 1

Two types of transplantation?

Answer 1

Solid organ
Bone Marrow/haemopoietic stem cells

Question 2

What gene determines rejection of transplant?

Answer 2

MHC or HLA in humans

Question 3

What gene codes for MHC and how many regions?

Answer 3

Chromosome 6
3 sections (Class 1,2 and 3 region)

Question 4

MHC Class types and their function

Answer 4

Class I MHC genes
Glycoproteins expressed on all nucleated cells
Present processed antigens to Tc

Class II MHC genes
Glycoproteins expressed on Macrophages, B cells, DCs
Present processed antigens to Th

Class III MHC genes
Products that include secreted proteins that have immune functions, e.g. complement system, inflammatory molecules

Question 5

Differences between MHC 1 and MHC 2

Answer 5

Lecture Slide
- MHC = B2 microglobulin, one transmembrane tail

Question 6

Inhertiance of HLA halotypes

Answer 6

Each child gets one copy of one HLA halotype from each parent

Question 7

ABO blood groups
For each group…
1. Antigen present
2.Antibody present
3.Blood group type and what blood can they recieve?

Answer 7

Type A blood has type A antigens
Type B blood has type B antigens
Type AB blood has both types of antigens.
Type O blood has neither A nor B antigens

Plasma from type A blood contains anti-B antibodies, which act against type B antigens. Can recieve A or O blood, NOT B or AB

plasma from type B blood contains anti-A antibodies, which act against type A antigens. Can recieve B or O, NOT A or AB

Type AB blood plasma has neither type of antibody. Can have any blood type

Type O blood plasma has both anti-A and anti-B antibodies. ONLY O group blood

Question 8

Preformed antibodies directed against antigens not present on RBC is due to…

Answer 8

The source is thought to be gastrointestinal and environmental bacteria, which possess ABO-like structures on their lipopolysaccharide coats causing
hemolytic transfusion reaction in ABO-incompatible (ABO-I) blood transfusion

hyperacute rejection in ABO-I organ transplantation.

Question 9

Draw the mechanism of rejection

Answer 9

Lecture Slide

Question 10

4 Types of transplants

Answer 10

Autograft–Transplantation of cells, tissues or organs between sites within the same individual e.g. skin graft.

Syngenic – close to auto graph as you can get, twins, genetically identical

Allograft– Transplantation of organs or tissues from a donor to a non-genetically identical individual of the same species.

Xenograft– Transplantation of an organ or tissue between two different species. ‘Pig valves’, for example, are commonly used to repair or replace a defective heart valve in humans.

Question 11

State if there is acceptance or rejection
1. Strain A to Strain A
2.Strain B to Strain A
3.Strain A to Strain A/B F1 hybrid
4.Strain A/B F1 hybrid to strain A
5.Guinea pig to strain A

Answer 11

Accept
Reject
Accept
reject
reject

Question 12

Clinical stages of rejection

Answer 12

Hyper acute rejection
Acute rejection
Chronic rejection
Graft versus Host

Question 13

Transplant rejection Table:
Hyperacute
Acute
Chronic
Graft vs host

Onset
Mechanism and symptoms
Type of hypersensitivity

Answer 13

Hyperacute:
Immediate
preformed antibodies directed against the donor tissue caused by ABO incompatibility . Presents with thrombosis and occlusion of graft vessels.
Type 2

Acute
Weeks to months
T cell mediated immune response directed against the foreign MHC. Inflammation and WBC infiltrate of graft vessels.
Type 4

Chronic
Months to years
T cell medicated process resultsing from the foreign MHC looking like a self MHC carrying an antigen. Causes intimal thickening and fibrosis of graft vessels.
Type 3 and 4

Graft vs host
Varies
Donor T cells in the graft proliferate and attack the recipents tissue. Causes diarrhoea, rash and jaundice
Type 4

Question 14

Cellular Responses to HLA Alloantigens 3 mechanisms

Answer 14

Allorecognition
Activation of the Immune Response
CD4+ T lymphocytes
CD8+ T lymphocytes

Three mechanisms
Direct
Indirect
Semi direct

Question 15

Describe the 3 types of alloantigen recog

Answer 15

Direct pathway
The donor’s antigen presenting cells (APCs), expressing foreign HLA, migrate to the secondary lymph nodes of the recipient and present donor antigens to the recipient’s CD4+ T cells.
The strength of the immune response elicited by the direct allorecognition pathway correlates to the high frequency of recipient allogeneic T cells that become activated during the first few weeks following transplant, mediating acute rejection.
believed to be the primary mechanism of acute rejection.

Indirect pathway
Donor antigens, shed by the grafted organ, are processed and presented in the context of self-restricted HLA class II by the recipient’s B cells.
The recipient’s follicular helper CD4+ T cells are then activated to provide help, leading to the generation of alloreactive CD8+ effector T cells and antibody-producing B cells

Semi direct pathway
Intact donor HLA class I:peptide complexes are presented on the DC of the recipient (through either membrane exchange or exosome uptake) to recipient CD8+ T cells.
Simultaneously, processed donor peptide is presented in the context of the recipient’s HLA class II to the recipient’s CD4+ T cells.
The recipient’s T-helper cells, activated by the indirect pathway, can then provide “help” to the recipient’s CTL, activated by the direct pathway.
overlap between the direct and the indirect pathways
The mechanism likely lies in the exchange of membrane proteins between immune cells.

Question 16

Preventing rejection Pre transplant and post transplant

Answer 16

Pre transplant
1. Compatible blood types
2.Genetic testing
3. Education/Support

post transplant
1.Montiroing
Anti rejection medication

Question 17

Immunosuppressive drugs do what?

Answer 17

interference with cell surface molecules
inhibiting signalling mechanisms
inhibiting T-cell proliferation
altering trafficking,
Alter the recruitment of immune cells responsible for rejection

Question 18

4 facts about immunosuppressive drugs and brief description

Answer 18

Given in two phases
Limitations e.g. immunodeficiency
Adverse side effects
Life time

Immunosuppressive drugs are given in two phases
initial induction phase involving a high dose
a later maintenance phase which involves using the drug in the long term at a lower dose

All current immunosuppressive drugs come with limitations. One of the major limitations of these drugs is immunodeficiency
As these immunosuppressive drugs are non-specific, they will reduce overall immune system function leaving patients susceptible to opportunistic infection.
A fine balance needs to be reached between suppressing immune functionsufficiently to avoid rejection, preventing drug toxicity, and maintaining enough immune function to fight off disease.

Many of these drugs are associated with adverse side effects, such as high blood pressure, impaired renal function, diabetes mellitus, and increased risk of cancer

Question 19

Mechanism of action of new immunosuppressive drugs Diagram

Answer 19

Lecture Slide
Cyclosporin
MPA
FTY720

Question 20

Finding an eligible donor-recipient match tests and description of test

Answer 20

ABO blood group compatibility– The donor and recipient are tested for compatible blood groups. This is the first test to be carried out as the transplant will be rapidly rejected if the blood groups do no match. In some transplants, for example young children and also bone marrow transplants, ABO compatibility is not a necessity.

Tissue typing– A blood sample is taken from the recipient to identify the HLA antigens present on the surface of the their cells to help find a histone compatible donor. The more alike the HLA types of the donor and recipient are the more likely a transplant will be successful. Family members, in particular siblings, are often the best HLA matches due to their genetic similarity.

Cross matching– Blood samples are taken from both the recipient and donor, and the cells of the donor are mixed with the blood serum of the recipient. If the recipient’s antibodies attack the donor cells, they are considered a positive match and transplantation will not be suitable due to increased risk of hyper-acute rejection.

Panel reactive antibody test– The blood serum of patients awaiting transplantation are tested for reactive antibodies against a random panel of cells. Previous exposure to foreign tissue, by blood transfusion, pregnancy or prior transplantations, are likely to increase the number of HLA antibodies in the blood. The more HLA antibodies present, the higherhe panel reactive antibody (PRA) level denoted to the patient, and the greater the chance of graft rejection. If PRA levels are high, it may be more difficult to find a match and a higher dosage of immunosuppressive drugs may be required.

Question 21

Tissue Typing methods and brief description

Answer 21

1.Micro cytotoxicity assay
2.Mixed lymphocyte culture (MLC)
3.Flow cytometry cross typing
4.DNA analysis

Microcytoxicity assay
Known antibody to WBCs of donor/recipient
Complement mediated lysis if antibody present on cell surface

Mixed lymphocyte culture (MLC)
Irradiated donor lymphocytes (stimulants)
Incubated with recipient lymphocytes
3H Thymidin incorporatin measured

Question 22

Draw and describe the Mixed lymphocyte culture (MLC) and Micro cytotoxicity assay

Answer 22

Mixed lymphocyte culture (MLC)
In this example, donor 1 and donor 2 are screened for suitability as tissue sources for a recipient. PBLs (the “stimulators”) isolated from each donor are irradiated and mixed with recipient PBLs (the “responders”).
T cells from the recipient are activated by direct allorecognition of donor cells and incorporate3H-thymidine into their DNA as they proliferate. High levels of radioactivity are detected in the cell culture indicating MHC mismatching.
The recipient T cells are not activated by donor 2 cells so negligible incorporation of3H-thymidine occurs, indicating MHC matching. Even if there had been minor histocompatibility differences between donor 2 and the recipient, little3H-thymidine uptake would be observed as the response to MiHA is relatively weak.

Micro cytotoxicity assay
This diagram shows serological typing. In the top diagram, the correct antibody for the HLA type of the cell was added, so complement activation occurred, leading to cell lysis. Cell lysis indicates that the antibody added matched the HLA type of the cell, so the HLA type of the cell is then known. In the bottom diagram, an HLA antibody that did not match the cell’s HLA type was added, so there was no complement activation, and no cell lysis occurred.

Question 23

Cross match diagram
What is a major vs minor crossmatch?

Answer 23

The main purpose of this test is to distinguish the appearance of antibodies in the recipient against the red blood cells of the donor.

Major crossmatch:
confirms the production of antibodies in the recipient against transfused red blood cell antigens (from the donor)

Minor crossmatch:
detects the presence of antibodies within the donor serum to the recipient’s red blood cells.