HLA, HSCT, Solid Organ Flashcards
Genes for HLA’s are on chromosome
6
What is the most polymorphic loci known in man
HLA, chance of two unrelated individuals having identical HLA types is very low
What is the HLAs function in the immune system
Antigen presentation, allorecognition-important immunological determinant for solid organ transplants
HLA Class 1
A, B, and C, present peptides from within the cell, digested viral proteins, self proteins or malignant cell proteins. Attract CD8+ cytotoxic T cells lead to cell death, adaptive immune response
Expression of HLA Class 1 prevents what?
Destruction by natural killer cells
Where do HLA class 1 reside
On most nucleated cells and platelets.
HLA Class II
DR, DQ, and DP. presents peptides from outside of the cell. Phagocytosed bacteria. Stimulate CD4+ T helper cells- stimulates antibody production, b cells, cytotoxic T cells and modulate immune response. These are on Antigen Presenting Cells (B cells, Marcophages, monocytes, dendritic cells intestinal epithelium, microvascular endothelium. Mostly DR, `20% DQ and very low DP
HLA class III
complement proteins C2 C4 TNF can be absorbed onto RBCs, chido=C4B rogers= C4a
Public Antigens
Less variable portion of the HLA molecule. Bw4 and Bw6 on almost all HLA-B molecules , can be very difficult to match if someone forms an antibody to a public antigen.
CREG
Cross-reactive antigen Group. Many common epitopes, antibodies bind common epitopes. Cross reactivity in serologic testing, unable to distiguish by serologic testing alone (HLA-B15 and B16)
HLA inhertiance
usually inherited as a haplotype
Finding an HLA matching sibling
Chance of sibling matching=25% formula = 1-(3/4)^n. n= number of siblings
Haplotype Match
sibling that inherited same haplotype from ONE parent
Genotype HLA match
sibling that inherited same genotype from BOTH parents
Linkage disequilibrium
When alleles of some haplotypes ocur more frequently than would be expected on the basis of chance alone. . Potentially due to survival advantage certain haplotypes are more likely to be inherited together.
European example of HLA linkage disequilibrium
A1 = 15% B8= 10% you would think the likelihood of them being inherited together would be 1.5 but it’s actually 7.8%
Recombination/Crossover
Genes that are closely linked. rarely occurs but creates new haplotypes. 0.8% between HLAA-and HLAB. 1.5% between HLA-B and HLA-DR
Microlymphocytotoxicity test
Serologic Detection of HLA antigens. HLA antibodies on plates. Lymphocytes from patient added. T and B cells- Class 1 typing. B cells- Class 2 typing. Rabbit complement added. Antiobidy binding causes complement activatin and cell death. Dye added, intact cells exclude dye and appear refractile. Dead cells incorporate dye; HLA type defined when antibodies cause lysis of >50% of patients cells. Grade is based off of color-death
HLA detection Molecular based
small samples increased TATs, n oneed for viable cells or antigen expression, high sensitivity and specificity
isograft/syngraft
graft or transplant of cells tissue or organ from one individual to another who is syngeneic (genetically identical)
Allograft
graft or transpant from one individual to an MHC disparate individual- nonhistocompatible or histoincompatible due to polymorphic HLA
xenograft
from donor and recipient of different species
hyperacute rejection
rejection due to- preformed antibodies against a component of graft or organ
acute rejection
thought to occur through T cells recognition of alloantigens on donor cells, insufficient immunosuppressants
chronic rejection
occurs months or years after transplant occurs, accompanied by proliferative inflammatory lesions of small arteries, thickening of glomerular basement membrane and interstitial fibrosis
Flow Cytometry in HLA typing is used for:
- HLA typing 2. HLA antibody ID 3. HLA crossmatching most common in transplant patient/donor
Mixed lymphocyte culture what it is
“cellular crossmatch” prior to transplant, takes 6 days but more sensitive than serology (microlymphotoxicity)
Mixed lymphocyte culture how it’s performed
lymphocytes from patient and donor cultured together. Each cell able to recognize the “foreign” HLA antigens of other-lymphocytes transform into blast cells - synthesize DNA and take up radioactive thymidine. if there is an uptake of radioactive thymidine this indicates lymphocytic activation
PRA
panel reactive antibody, identifies antibody specificity and antigens to avoid from donor in future transfusions
Single antigen bead assay
polysteryne beads impregnated with different concentrations of dyes, 100 unique beads can be coated with different HLA antigens,Patient plasma is added-HLA antibodies will bind to corresponding antigen on bead. PE labeled IgG added and binds to IgG that is bound to the bead, emits fluorescence- detectable each antigen=specific fluorescence
Cyototoxic crossmatch
HLA anitobdy crossmatch, recipient serum and donor lymphcytes (MUST BE FRESH WITHIN 48 HOURS) this is used to prevent a hyperacute rejection
Flow cytometry in antibody testing for HLA can be an advantage because (2)
It is more sensitive and it discriminates IgG vs IgM
Positive cytotoxic crossmatch results indicate:
contraindication for transplant
Bennett good speed HLA antigens (3) and problems they cause
Bga-B7 Bgb-8 Bgc-A28, antibodies against these may react against red cells with HLA remnants
HLA match classifications/codes
A (4anitgen match this is the best) B1V-3 anitgens fourth is unknown B1X-3 antigens 4th is reactive, B2U, B2X, B2UX, C, D -in order of most compatible to least compatible
Solid organ transplants- priorities in compatibility per organ
ABO compatibility is the most important. Liver HLA matching may have no effect. Hear some centers match for HLA type, Degree of HLA compatibility corresponds with graft survival
birdshot retinopathy HLA correlation
A29
Type 1 diabetes correlation
DQ3
Autoimmune disorders/ disease due to molecular mimicry: 1Rubella 2HTLV1- 3Herpes- 4EBV- 5Sterp- 6Mycobacteria- 7H1N1 Flu-
1 Type 1 Diabetes
- Associated myelopathy
- Stromal Keratitis
- Multiple sclerosis, lupus and parkinson’s
- rheumatoid myocarditis
- bilary cirrhosis
- narcolepsy
Ankylosing Sponylitis correlation
HLA B27, 90% gene related predominantly male
Steven Jonson’s syndrome hyperreactivity ***
Allopumol Carbamazapen
G in allele nomenclature
HLA allele that encodes for identical nucleotide in peptide binding domain. Identical DNA = G code
P in allele nomenclature
HLA alleles that share identical nucleotide
sequences for the EXONS encoding the peptide
binding domains- Identical Protein for the peptide pinding domain =P code
Stem Cell donor/recipient match
3/6 match or Haplomatched donor
Choloroquine diphosphate effect on HLA antigens
removes 80% of HLA antigens
