CH 15: Transplantation of Tissues and Organs

What are alloantigens?

antigens that differ between members of the same species, causing an immune response in transplants

What is an alloreaction?

an immune response against alloantigens

What is histocompatibility?

when a donor and recipient’s tissues are similar enough in regards to antigens and MHC molecules

What is an autograft - AKA: autogenic transplant?

transplantation of tissue from one site to another on the same individual

Ex: skin graft of burn victim

What is an allograft?

a transplant of tissue or organs between genetically different individuals of the same species

What type of histocompatibility and success rate do autografts have?

100% success rate due to the perfect histocompatibility

What type of histocompatibility and success rate do allografts have?

Never perfect histocompatibility due to immune responses being made to the alloantigens between donor and recipient.

What is the most common type of transplant?

A blood transfusion

What antigens are involved in blood transfusions and must be matched for first time infusions?

ABO and Rhesus D antigens

What happens if incompatible blood is transfused?

The recipient’s immune system will attack the transfused red blood cells

Who can receive type O blood?

Anyone, it is the universal donor

But type O individuals can only receive from other type O individuals

What is an ABO antigen?

a protein or sugar found on the surface of red blood cells that determines your blood type as A, B, AB, or O

What antigens does someone with blood type A have on their red blood cells?

They have A antigens

Which means B antigens are foreign

What antigens does someone with blood type B have on their red blood cells?

They have B antigens

Which means A antigens are foreign

What antigens does someone with blood type AB have on their red blood cells?

They have A and B antigens

What antigens does someone with blood type O have on their red blood cells?

They have no surface antigens

Which means A and B antigens are foreign

Who can Rh- people give their blood to?

Rh- people and Rh+

Because, they are negative for RhD antigen, so they aren’t forgein to RhD + who has RhD antigen

Who can Rh+ people give their blood to?

Only Rh+ people

Because, they have the RhD antigen, so giving that to an Rh- would make the antigen seen as foreign

Why aren’t MHC molecules matched in blood transfustions?

Red blood cells barely have any MHC molecules and the white blood cells, which do have MHC molecules, are removed before the transfusion occurs

What is the major antigen that has to be matched at least a little bit for an organ transplant?

MHC molecules

Fewer mismatches=better chances of the organ lasting a long time

(ABO antigens are already matched before this)

What are the main types of rejection in organ transplant?

Hyperacute, acute, and chronic rejection

Why do MHC molecules need to be matched, or at least somewhat matched?

MHC molecules are proteins on cells that help the immune system to recognize “self” from “non-self”. So if the recipient and donors MHC molecules don’t match, the Immune system may attack the new organ because it seems foreign

What causes hyperacute rejection?

Pre-existing antibodies against the donor MHC or ABO antigens.

How fast does hyperacute rejection happen?

Within minutes to hours after the transplant

What people are most at risk for hyperacute rejection?

Donor/recipient who are ABO incompatible

Recipient who has already been exposed to other MHC molecules through pregnancy, blood transfusions, and previous transplants

What causes acute rejection?

Recipient T cells recognize donor MHC molecules as foreign and attack the organ.

What are the 2 mechanisms involved in acute rejection?

Direct recognition and Indirect recognition

What is direct recognition in acute rejection?

Donor dendritic cells present donor MHC:peptide complexes to recipient T cells and activates the recipient T cells, which leads to the destroying of donor cells with the same complex. Leads to damage of the organ

What is indirect recognition in acute rejection of a solid organ transplant?

The recipient dendritic cells take in donor MHC:peptide complexes, then process those complexes and activate recipient T cells to attack. The T cells recruit macrophages and antibody production to the donor complexes. This leads to damage in the blood vessels and tissues over time

What causes chronic rejection?

Minor alloantigens

They cause inflammation and narrowing of blood vessels, which leads to reduced blood flow to the organ, causing it to slowly lose function

What is a minor histocompatibility antigen?

a small protein difference between donor and recipient cells that can still trigger an immune response, even if their major MHC molecules match. these antigens can cause slower rejection

What are hematopoietic stem cells?

special cells that can turn into all different types of blood cells.

What are the 3 sources to get hematopoietic stem cells?

Bone marrow (inside of bones)

peripheral blood (the cells are lured out of the bones with drugs then taken up)

umbilical cord blood (collected from cord of a new baby after birth then stored in blood banks)

What is a hematopoietic stem cell transplant?

a procedure where healthy blood-forming cells are given to rebuild a person’s entire blood and immune system after it has been damaged by treatments like chemotherapy or radiation.

What is acute graft vs host disease? (GVHD)

After a hematopoietic stem cell transplant, the donor T cells see the recipient’s body as foreign and launch an immune response against its cells, mainly in the gut, liver, and skin

What is the best way to prevent rejection during a hematopoietic stem cell transplant?

Matching MHC molecules between the donor and recipient

The MHC molecules will help the donor see the recipient as okay and not foreign

What are the 2 best ways to find a MHC match?

a full sibling (1/4 chance)

an unrelated donor who might have the same MHC combo as you