HLA in transplant and transfusion

Question 1

What are human leucocyte antigens a product of?

Answer 1

The major histocompatibility complex (MHC)

Question 2

Compare the structure of HLA class I and II

Answer 2

Class I = alpha polypeptide chain with 3 domains and two beta2 microglobulin

Class II = dimeric glycoprotein, light and heavy chains, each with 2 extracellular domains (alpha1+2, beta1+2)

Question 3

Compare the peptide bonding of HLA class I and II

Answer 3

Class I =
- 8-10 aa long
- Degraded intracellular proteins
- Pathogen derived peptides presented by it are recognised by CD8+ T cells
- Majority of polymorphism in alpha1 and 2 domains
- Expressed on most nucleated cells

Class II =
- Peptides 10-30 aa long
- Extracellular derived
- Peptides presented by it recognised by CD4+ T helper cells
- Majority of polymorphism in beta1 domain
- Expressed on APCs

Question 4

Which chromosome is human MHC found on?

Answer 4

Chromosome 6

Question 5

How are HLA alleles inherited?

Answer 5

As linked groups (haplotypes)

Question 6

Outline HLA polymorphism

Answer 6

• Most polymorphic system in genome
• Related to function of peptide presentation
• In the peptide binding region (PBR), usually driven by natural selection
• High levels of coding mutations in the PBR

Question 7

What are uses of complement dependant cytotoxicity?

Answer 7

• Detects complement-binding antibodies
• Low resolution typing (cannot define all specificities, time consuming)
• HLA antibody screening (very sensitive to IgM, use of frozen cells, limitless cell panel)

Question 8

What is CDC crossmatch?

Answer 8

• Isolating donor cells and exposing them to recipient serum (with the addition of exogenous complement)
• Detects preformed antibodies present
• Separates T and B cells to detect class I or II

Question 9

What is used in CDC to eliminate IgM?

Answer 9

DDT (Dithiothreitol)

Question 10

How does flow cytometry crossmatch distinguish between immunoglobulin classes?

Answer 10

Hsing anti-human IgG or IgM

Question 11

Outline ELISA HLA antibody screening

Answer 11

• Rapid compared to CDF
• Detects only IgG
• Usually two tests
• Limited number of cells used

Question 12

Outline PCR SSO typing

Answer 12

• Robust but high ambiguity rate
• Suitable for automation
• Capable of high resolution typing
• Beads incubated with sample, washed before adding PE
• Analysed with Luminex (96 plate well)

Question 13

Outline SBT (Sanger sequencing)

Answer 13

Similar to PCR in DNA

BUT, only uses a single primer and polymerase to make new ssDNA pieces

Includes regular and dideoxy nucleotides

Question 14

State four types of HLA in transfusion

Answer 14

Febrile non-haemolytic transfusion reactions
Transfusion related acute lung injury (TRALI)
Transfusion associated graft versus host disease (TaGVHD)
Platelet refractoriness