HLA

Question 1

T or F: In humans, MHC = HLA

Answer 1

TRUE; In humans, MHC = HLA
- This is the bar code of the immune system and is how ‘self’
from ‘non -self’ is distinguished

Question 2

Major function of MHC

Answer 2

presentation of antigens to T cells

Question 3

MHC genes

Answer 3

• many genes
• but NOT ALL are functional or relevant in transplantation

Question 4

HLA

Answer 4

Human Leukocyte Antigens:
- protein molecules expressed on cell surfaces

MHC I = on all nucleated cells and platelets
MHC II = on professional APCs (dendritic cels, B cells, macrophages)

Question 5

HLA alleles

Answer 5

• allele = different DNA sequence at a given locus
• polymorphic; different DNA sequences for that gene

Question 6

HLA inheritence

Answer 6

• HLA genes located on Chr 6
• Mendelian inheritance = co-dominantly expressed (maternal and paternal both expressed)
• inherit A, B, DR antigens*

*NOTE: think of HLA antigens like C, D, E in Rh blood grouping

Question 7

HLA is associated with which autoimmune diseases ?

Answer 7

• Celiac
• Type 1 diabetes
• Multiple sclerosis

Question 8

HLA is associated with which drug sensitivities ?

Answer 8

• Abacovir
• Carbamezapine

Question 9

HLA typing

Answer 9

• part of transplant work up
• 6 loci of interest:
  MHC I = A, B, C
  MHC II = DP, DQ, DR

Question 10

Traditional HLA typing in solid organ transplantation

Answer 10

MHC I = A, B
MHC II = DR

Question 11

Why does HLA typing matter ?

Answer 11

• typing donor allocates better HLA matches
• also helps to interpret antibody specificities, explain, and interpret crossmatch results

Question 12

Describe Traditional HLA Typing

Answer 12

• laborious
• serological Complement Dependent Cytotoxicity (CDC) method
• Lymphocytes are isolated and tested against numerous anti-sera (~300)
• Addition of rabbit complement = cell lysis/death if HLA antibodies attach

Question 13

Sequence-Specific Primer Technique

Answer 13

• Primers specific for every allele of interest must be included; series of primers are used like anti-sera
• many primers are required to cover common HLA alleles

NOTE: not commonly used anymore

Question 14

Describe Reverse SSO Typing Method

Answer 14

• replaced SSP typing methods
• loci are amplified and many probes are used to detect the different alleles
  — isolated DNA is amplified with HLA locus-specific primers
  — PCR product is biotinylated
  — incubated with probe-labelled beads + Streptavidin-PE labelled conjugate
  = PE fluorescent on beads is measured
• uses Luminex instrument
• can run batches or single samples

SSO = sequence-specific oligonucleotide
SSP = sequence-specific primer

Question 15

Advantages of DNA-Based Typing vs Serology CDC

Answer 15

• DNA-based typing doesn’t need viable lymphocytes; serological does
• Age of specimen and conditions of transport are less important in DNA-based Typing
• Easier to create a primer for an HLA antigen than to screen antisera for HLA specificities

Question 16

Limitations of DNA-Based Typing

Answer 16

• Lymphocytes are still necessary for other
  transplant related testing such as the crossmatch
• Potential DNA contamination demands stringent laboratory set-up and training
• New alleles are always being identified so the software must also be frequently updated

Question 17

How are null alleles involved in DNA-Based Typing ?

Answer 17

Rare “null” alleles are detected by DNA-based typing but not expressed on the cells

NOTE: patient can still make an Ab to “null” allele that is not expressed