4.2. Transplants and transfusions

What are the steps in blood compatibility testing?

1) Mix patient blood with reagents containing A, B or Rh antibodies 2) Observe for agglutination 3) Agglutination = incompatible; no agglutination = compatible

What does agglutination indicate in blood typing?

The blood has reacted with a certain antibody and is therefore not compatible with blood containing that antigen

What does the absence of agglutination indicate?

The blood does not have the antigens that bind the antibody in the reagent

What is the Bombay blood group?

An extremely rare blood group characterised by the absence of the H antigen on RBCs

Why is the Bombay blood group particularly challenging?

Individuals can only receive blood from other Bombay blood group individuals, making compatible donors extremely rare

Why is the Bombay blood group often misclassified?

It is often mistakenly classified as blood type O because individuals lack typical A, B, and O antigens

What role do specialised blood banks play in rare blood types?

They collect, store, and distribute rare blood types to ensure individuals with unique requirements have access to compatible blood

Why is blood type O thought to have a survival advantage against some diseases?

Type O individuals have antibodies against both A and B antigens, which can neutralise certain pathogens

Why did the ABO blood group system evolve?

Due to selective pressures associated with diet and infectious diseases

Where are ABO antigens found besides RBCs?

In various body tissues and fluids, including the gastrointestinal tract

What is the dietary hypothesis of ABO evolution?

Blood type A individuals may have adapted better to plant-based diets, while blood type B individuals may have adapted better to diets with more animal products

What advantage may blood type O individuals have against cholera?

Cholera toxin binds less effectively to the intestinal cells of type O individuals, potentially reducing infection severity

What advantage may blood type O individuals have against malaria?

The Plasmodium parasite binds less effectively to their RBCs, offering some protection against severe forms of malaria

How do ABO antigens interact with pathogens?

ABO antigens may serve as receptors or binding sites for certain pathogens; differences in structure and abundance affect how pathogens attach to host cells and evade the immune system

How may blood type affect immune response to infections?

Blood type A individuals may have different immune responses to certain infections compared to type B individuals due to variations in antigen presentation

What is HLA typing?

Human Leukocyte Antigen typing — a crucial aspect of organ transplantation used to minimise the risk of graft rejection

Where are HLA antigens found?

On the surfaces of immune cells (leukocytes)

Where are HLA genes located?

On chromosome 6 in humans

What are the two classes of HLA genes?

Class I and Class II

What do Class I HLA molecules do?

Present peptides to CD8+ T cells, which kill infected or abnormal cells

What do Class II HLA molecules do?

Present peptides to CD4+ T cells, which regulate the immune response

Why is HLA typing critical in organ transplantation?

To reduce the chance of the recipient's immune system recognising the transplanted organ as foreign and attacking it

What blood types can blood group A receive?

A or O

What blood types can blood group B receive?

B or O

What blood types can blood group AB receive?

A, B, AB, or O — AB is the universal recipient

What blood types can blood group O receive?

O only — O is the universal donor

What are the Rh factor transfusion rules?

Rh+ can receive Rh+ or Rh- blood; Rh- can only receive Rh- blood

What is crossmatching in blood transfusion?

Mixing a small sample of donor and recipient blood to check compatibility before transfusion

What are the possible outcomes of crossmatching?

Successful transfusion, febrile reactions, haemolysis, circulatory overload, immunogenic response, allergic response, or agglutination