L19: Transplantation

Question 1

What are alloantigens?

Answer 1

antigens which vary between members of the same species

Question 2

What are alloreactions?

Answer 2

immunes responses directed against alloantigesn

Question 3

What are immunogenetics?

Answer 3

subfield of immunology devoted to the genetics of alloantigens

Question 4

What is an autograft?

Answer 4

graft of tissue from one site to another site on the same individual (no rejection results)

Question 5

What is an isograft?

Answer 5

aka syngeneic graft. graft of tissue from one individual to another individual that is genetically identical (no rejection results).

Question 6

What is an allograft or allogeneic transplant?

Answer 6

graft of tissue from one person to another person that is genetically different (rejection can occur)

Question 7

What is graft vs. host reaction (GVH)?

Answer 7

reaction mounted by mature T cells contained within grafted tissue against tissues of the recipient

Question 8

Why are RBCs easy to transfuse and do not usually illicit immune response?

Answer 8

RBCs do not express MHC class I or class II molecules, so there is little rejection by the immune system. Transfused blood is usually only needed for a short time anyway.

Question 9

What can cause an alloreaction after a blood transfusion?

Answer 9

if the blood types were not matched, the structural polymorphisms in the carbohydrates on glycolipids of the RBC surface would react with antibodies in the host circulation.

Question 10

Can A type blood be given to an AB type patient?

Answer 10

yes.

Question 11

Can A type blood be given to an O type patient?

Answer 11

no, alloreaction will occur.

Question 12

What are the clinical signs of blood transfusion alloreaction?

Answer 12

fever, chills, shock, renal failure, and sometimes death. Very similar to type II hypersensitivity reaction

Question 13

What are Rh factors?

Answer 13

a set of 50 blood group antigesn that are polymorphic with rescpect to expression in the poplation. RhD is the most important. It is commonly referred to as Rh factor.

Question 14

Can an Rh+ patient be given Rh- blood? Can an Rh- person be given Rh+ blood.

Answer 14

yes.

no a Rh- person can only receive Rh- blood otherwise alloreactions will occur

Question 15

Would you expect any complications in a Rh- mother who is giving birth to her second Rh+ child? There were no complications with the first child.

Answer 15

Yes. The mother was exposed to fetal blood during the first pregnancy and developed an IgG response to it. IgG can cross the placenta and will attack the second fetus. This is prevented with RhoGam treatment during the first pregnancy.

Question 16

What is panel-reactive antibody (PRA)?

Answer 16

a test of a donor seeking patient against the sera of multiple donors to see who they are reactive against

Question 17

What is acute graft rejection mediated by?

Answer 17

effector T cells that respond to HLA differences between the donor and recipient. there was no previous exposure to donor tissue or preformed response.

Question 18

What is the direct pathway by which HLA can stimulate acquired immune responses?

Answer 18

naive T cells of the recipient recognize self peptides of the donor loaded onto donor HLA molecules on donor APCs

Question 19

What is the indirect pathway by which HLA molecules can stimulate acquired immune responses?

Answer 19

peptides derived rom donor HLA molecules are processed and presented by recipient APCs to naive T cells of the recipient; the source of these donor HLA molecules is primarily donor APCs which migrate to secondary lymphoid tissue of the recipient and undergo apoptotic death. The components of theses dead cells are phagocytosed and processed via MHC class II processing, generating a CD4 T cell response.

Question 20

What is minor histocompatability antigen-mediated rejection?

Answer 20

ersults from immune responses to mino histocompatability antigens (when donor and recipient are identically matched with respect to MHC expression). There are other polymorphic genes that can impact transplant outcome. Usually takes about 60 days.

Question 21

What is chronic rejection?

Answer 21

can occur months or years after transplantation. Typically correlates with the presesnce of antibodies specific for MHC class I molecules of the grafted tissue. Is characterized by reactions in the vasculature of the graft that result in thickening of the vessel walls and narrowing of their lumina. Mediated by MHC class I specific antibodies that bind to vascular epithelia and attract Fc receptor bearing cells. Responsible for more than 50% of all kidney and heart transplants

Question 22

In what tissues is HLA matching not necessary?

Answer 22

corneal tarnsplants, because the cornea is not vascularized.
Liver transplants, because liver has specialized architecture and vasculature and the hepatocytes express very low levels of HLA class I or III.

Question 23

Where does GVHD usually attack?

Answer 23

skin, GI, liver. mediated by mature T cells in donor tissue.

Question 24

What is a zenograft?

Answer 24

graft between two individual of different species

Question 25

What mediates hyperacute reaction?

Answer 25

pre-formed antibodies, which activate complement cascade and other fast responses, killing the donor tissue. (usually a mixture of IgM and IgG)

Question 26

Would an A blood type patient who suffered from hyper-IgM syndrome and received an AB type kidney within 48 hours?

Answer 26

Yes. IgM is a very potent activator of complement cascade. They will kill it fast.

Question 27

How long would you expect it to take for a person with a minor histocompatibility antigen issue to develop a rejection response?

Answer 27

30-60 days in most cases

Question 28

What are the three most important HLA loci for donor matching?

Answer 28

HLA-A, HLA-B and HLA-DR

Question 29

What do Th2-type cytokines do?

Answer 29

upregulate humoral responses and downregulate cell-mediated responses. Secreted by fetal tissue.