Term
| Major Histocompatability Complex |
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Definition
| MHC. The group of genes on chromosome 6p that encode the human leukocyte antigens (HLA). These play a role in organ transplant rejection. If the donor and the recipient have matching HLAs, success is more likely. If they don't match, T and B lymphocytes will attack the transplant (graft rejection). |
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Term
| Graft-Versus-Host-Disease |
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Definition
| GVHD. The cells of the donor organ recognize the host as foreign and attack it. |
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Term
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Definition
| HLA identification. Usually serology methods to detect HLA antibodies. DNA typing can also be used. |
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Term
| Class I MHC Gene Products |
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Definition
Found in all nucleated cells. Function in the identification and destruction of abnormal/infected cells by cytotoxic T cells.
Produce HLA-A, HLA-B, and HLA-C. |
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Term
| Class II MHC Gene Products |
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Definition
Found in B lymphocytes, macrophages, dendritic cells, activated endothelial cells, skin cells. Function in ID of foreign antigens by helper T cells.
Produce HLA-D. |
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Term
| Class III MHC Gene Products |
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Definition
Found as plasma proteins and help defend against extracellular pathogens.
Produce compliment C2, C4, B. |
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Definition
| Code plasma proteins TNF-alpha and TNF-beta, which help with cell growth and differentiation. |
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Definition
- HLAs Class I, II, III
- Cytokine genes (tumor necrosis factors alpha and beta) |
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Definition
xMHC. 8 Mb.
-Hemacromatosis gene HLA-F (HFE) is farthest telomeric gene.
- Tapasin (antigenic peptide processing) is most centromeric. |
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Term
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Definition
Two transmembrane polypeptides:
-alpha chain of alpha1, alpha2, alpha3 domains.
-beta chain of beta1 and beta2 domains.
The two are associated, forming a groove between alpha1 and beta1 to hold antigens that have been engulfed and processed by the cell. |
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Term
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Definition
Two parts:
- Long (heavy) chain 346 AA in length.
- Beta-2 macroglobulin 99 AA (not MHC) encoded.
The two are associated on the cell surface by non-covalent bods.
The heavy chain is a transmembrane glycoprotein.
Bind to antigens generated by the cell. |
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Term
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Definition
The collection of alleles in the HLA genes. HLA genes are highly polymorphic, matching only in twins.
Exons 2,3 of class I genes and exon 2 of Class II genes have the most polymorphisms. They code for AAs involved in antigenic peptide interactions, affecting recognition of non-self molecules. |
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Term
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Definition
Polymorphisms are shared by at least 2% of the population, mutations and variants occur less often. Alleles of the HLA gene differ at the DNA level by nuc sequence and at the protein level by AA sequence and antigenicity.
Gene conversion events and rare chromosomal recombinations create polymorphisms.
Maternal and paternal HLA variants are expressed codominantly as antigens on the cell. |
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Term
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Definition
| If a specific allele codes an antigen recognized by an antibody that binds to several antigens, that allele will be impossible to call. It will be denoted as a range of possible alleles. Some methods can't assign heterozygous alleles to one or another chromosome, leading to ambiguous results. |
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Term
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Definition
Level of allelic determination.
Low resolution detects a broad group of alleles.
High resolution can discriminate between specific alleles.
Low resolution can be used for solid organ transplants, but high resolution is needed for bone marrow or stem cell transplants. |
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Definition
1900 HLA alleles have been identified. Molecular methods detect more alleles than serology.
Allele identification helps with selection of organ donors and determination of organ survival length and with the association of HLA alleles linked to disease. |
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Definition
Antigen-antibody recognition used for organ transplants. Affords only low resolution, but is rapid and reveals immunologically relevant epitopes. It can also resolve ambiguities or confirm null alleles.
Patient cells can be tested with antisera or sera can be screened for anti-HLA antibodies. |
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Term
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Definition
| Screening of antihuman antibodies in serum that match known HLA alleles. |
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Definition
| Initial ID of HLA alleles using protein or DNA methods. Can define haplotypes and look for HLAs associated with diseases. |
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Definition
| Screening of recipient sera for antibodies against antigens from potential organ donors. |
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Definition
The complement dependent cytotoxicity test types lymphocytes. A plate is preloaded with antibodies of known HLA types. Different antibodies are used depending on the geographical area/ethnicity. Lymphocytes from either the donor or the recipient are placed in each well. Cells that are disrupted due to antibody reactions take up trypsin dye/eosin red dye. Cytotoxicity is determined by percent of cells in each well that are dead. This is subjective, so two techs should score it.
Cytotoxicity over 6 indicates the cell had antigens to the antibody in that well. |
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Term
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Definition
| Antigens have multiple epitopes, some of which are found on other HLA antigens (cross-reactive epitope groups). Private antibodies bind to one specific HLA type. Antibodies that bind to CREG can also be used. Some epitopes are more important than others if they mismatch, and others can be non-matching as long as key epitopes match. |
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Definition
| People's serum usually doesn't contain antibodies against human antigens (antihuman antibodies or alloantibodies). If they do have alloantibodies it may be due to pregnancy, blood transfusions, or prior organ transplant. This may mean that the alloantibodies will attack a donor organ, so specificity of alloantibodies in the recipient must be determined and a donor organ chosen that doesn't have complimentary antigens. |
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Definition
Antibodies from patient serum are added to well containing reference lymphocytes of HLA types occurring in the general population. Reference lymphocytes react to panel reactive antibodies (PRA). When patient antibodies are tested, it shows what percent of the population the patient will cross-react with. %PRA refers to the percent of lymphocytes killed by patient antibodies.
%PRA over 50% indicates a highly sensitized patient. Finding suitable donors will be hard. |
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Term
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Definition
| Antigens of known HLA types are attached to beads. Test serum is applied to the beads and antibodies in the test serum that match those antigens will bind to the beads. Unbound antibodies are removed and labeled secondary reporter antibodies are added. Labelled beads are detected by flow cytometry. This is a less subjective test than %PRA, but it can't determine the specific antibodies present, only the prevalence of antihuman antibodies in patient serum. Known antigens can be attached to beads of different fluorescence to increase specificity. |
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Definition
Recipient serum provides antibodies to be tested against donor lymphocytes. If the donor lymphocytes die, it is a positive crossmatch and prevents transplants.
Enzyme-linked immunosorbent assays use solubilized HLA antigens and help monitor antibody production over time, or humoral sensitization development after transplant. |
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Term
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Definition
MLC. T lymphocytes are responsible for organ rejection, so cross-reactivity of T cells between donor and patient is tested by measuring growth of lymphocytes activated by cross-reactivity. MLC can also predict GVHD by testing cell-mediated cytotoxicity and cytokine production.
Cells are incubated together for a few days. More accurate than serology, but more difficult. |
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Term
| HLA Protein Gel Electrophoresis |
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Definition
| Proteins from HLA genes can be separated by IEF gels or 2D gels. This method is limited to proteins with different net charges. |
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Term
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Definition
Initially done with RFLP on Southern blot, to detect HLA class II alleles.
Can identify more alleles than serological methods. Organs matched by DNA typing survive longer.
Blood is collected in EDTA tubes. |
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Term
| Sequence-Specific Oligonucleotide Probe Hybridization |
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Definition
SSOP. HLA antibodies immobilized on a dot blot are hybridized to a labeled probe. Class II, exon 1 and Class I, exons 2 and 3 genes are highly polymorphic and the primers usually target them.
70 uL of PCR product is needed. After soaking in NaOH to denature them, amplicons are spotted to the membrane. The membrane is dried and cross-linked before probes are used. 30 probes are usually used, and a separate membrane is needed for each one. Positive (probe complimentary) and negative (noncomplimentary) controls are used. |
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Term
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Definition
| 19-20 b long, ssDNA. Covalently attached to biotin or digoxygenin. Probes are designed to match HLA polymorphic sequence alignments to the polymorphic nucleotide is in the middle of the sequence. The hybridization conditions depend on probe binding less effectively if one base is off. |
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Term
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Definition
Low to intermediate resolution.
Intermediate HLA-ORB results require 30-60 probes.
High resolution of HLA-A, HLA-B, and HLA-C can be achieved using 67 A probes, 99 B, and 57 C. Intermediate resolution requires 39 A and 59 B. |
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Term
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Definition
| SSP-PCR. Since the 3' end of the primer must be strictly complimentary, placing the 3' end in a highly polymorphic region would help you identify the presence or absence of a specific allele by the presence of the amplicon or not. Faster than SSOP. |
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Definition
Patient DNA is added to a 96-well plate. Each well has a different set of primers for a specific allele. Amplification controls are also included, and should give results for every sample. Sequence-specific primers will produce a product only if that specific allele is present. Amplification controls produce a product of different length than SS primers. If primers match the patient allele, the product will show up on a gel. If not, only the amplification control will be present.
Class I and II DRB and DRQ genes can be tested this way. |
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Term
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Definition
Good for HLA typing and discovery and analysis of new polymorphisms. A polymorphic region (e.g., exons 2 and 3 of HLA-B) are amplified first using PCR primers for the whole region and then using specific primers for the exons. The amplicons are cleaned and run on a gel and sequenced for polymorphisms. HLA types are often heterozygous and will yield such a pattern.
Secondary structure can alter the behavior of fragments. |
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Term
| Heteroduplex Analysis Typing |
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Definition
| Can be used on the HLA-DR or HLA-DP to determine bone marrow compatibility. Reference strand conformation polymorphism can be used, where amplicons are mixed with fluorescent fragments of a known sequence before denaturation and heteroduplex formation. Capillary gels are used to resolve the homo- and heteroduplex formed between amplicons and reference strands. Limited use due to complexity and strict reaction demands. |
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Term
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Definition
HLA alleles can differ by just one nuc. Serology won't detect these differences and also relies on the correct cell type being collected (only B cells carry Class II antigens, etc.). DNA testing can be done on any cell type, since the DNA sequence is the same. Synonymous DNA changes and polymorphisms outside the target won't be detected, but may change antigenicity. Probe/primer design determines level of resolution. Only HLA types targeted for will be detected.
Results can be combined from DNA and serology to give better definition. Repeating DNA tests (SSP-PCR and then PCR-RFLP) can refine results. |
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Term
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Definition
Serology and DNA test results may conflict.
- DNA-detected alleles may not change antigenicity.
- Serology results may be homozygous because they don't recognize the second allele detected by molecular methods.
- DNA tests may identify homologous sequences that are detected by serology as a new result. |
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Term
| Minor Histocompatibility Antigens |
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Definition
Proteins outside the MHC that can be recognized as non-self and can contribute to GVHD and transplant failure in MHC-identical transplants.
mHags include: H-y, HA-I, CD31, HPA-1, HPA-2, HPA-3, HPA-5.
Comparative genomics could be used to find new mHags. |
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Term
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Definition
Class I MICA and MICB genes can be found in MHC, in addition to pseudogenes MICC, MICD, MFCE. These are found on Chr6p21.3 along with retinoic acid early transcript (RAET) gene. The products of these genes bind to natural killer cells with NKG2D receptors. They control immune response to tumor cells by controlling killer cells and cytotoxic T lymphocytes.
MICA has 60 allels, MICB 30. These alleles are in coding regions, not hypervariable ones. Anti-MIC antibodies may appear after organ transplant. |
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Term
| Killer Cell Immunoglobulin-like Receptors |
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Definition
KIR. Expressed by NK and memory T cells. Can contribute to graft rejection even when the immune system is compromised. They interact with HLA-A, B, and C (class I)
molecules. They can be expressed on myelomonocytic lineage cells and other leukocytes. Their genes cluster on 19q13.4, the leukocyte receptor cluster.
KIR polymorphisms may be analyzed for transplants to find donors and recipients that don't match. An SSO bead system or SSP can be used. |
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Definition
| Autoimmune diseases (4% of population) are linked to MHC. HLA haplotypes contribute to rheumatoid arthritis, multiple sclerosis, diabetes mellitus type I, systematic lupus erythematosis. Other genes, epigenetic, and environmental factors contribute as well, making haplotype presence alone non-diagnostic. MGC genes can protect from diseases, too. Some HLA types are "protective" against HIV. |
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