HLA Flashcards
T or F: In humans, MHC = HLA
TRUE; In humans, MHC = HLA
- This is the bar code of the immune system and is how ‘self’
from ‘non -self’ is distinguished
Major function of MHC
presentation of antigens to T cells
MHC genes
- many genes
- but NOT ALL are functional or relevant in transplantation
HLA
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)
HLA alleles
- allele = different DNA sequence at a given locus
- polymorphic; different DNA sequences for that gene
HLA inheritence
- 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
HLA is associated with which autoimmune diseases ?
- Celiac
- Type 1 diabetes
- Multiple sclerosis
HLA is associated with which drug sensitivities ?
- Abacovir
- Carbamezapine
HLA typing
- part of transplant work up
- 6 loci of interest:
MHC I = A, B, C
MHC II = DR, DQ, DP
Traditional HLA typing in solid organ transplantation
MHC I = A, B
MHC II = DR
Why does HLA typing matter ?
- typing donor allows potential for allocation according to degree of HLA match
- typing also helps to interpret antibody specificities, explain, and interpret crossmatch results
Describe Traditional HLA Typing
- laborious
- involves a serological Complement Dependent Cytotoxicity (CDC) method
- Lymphocytes are isolated and tested against numerous anti-sera (~300)
- Addition of rabbit complement initiates cell lysis if HLA antibodies attach
= Cell lysis/death is observed
Sequence-Specific Primer Technique
- 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
Describe Reverse SSO Typing Method
- 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 produce 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
Advantages of DNA-Based Typing vs Serology CDC
- A serological based typing requires viable lymphocytes
- Age of specimen and conditions of transport are much less important in DNA-based Typing
- It is easier to create a primer for an HLA antigen than to screen antisera for HLA specificities
Limitations of DNA-Based Typing
- Lymphocytes are still necessary for other
transplant related testing such as the crossmatch - Potential DNA contamination demands stringent laboratory set-up and training
- Rare “null” alleles will be detected by DNA but not expressed on the cells
— patient can still make an Ab to “null” allele that is not expressed - New alleles are always being identified so the software must also be frequently updated
