HLA antigens are integral cell membrane glycoproteins, which play key roles in immunity. These molecules represent major barriers to organ and tissue transplantation between individuals, but have also been implicated in many disease processes, particularly those with an autoimmune component. Two distinct classes of structurally similar HLA antigens have been well characterized and differ in their tissue distribution - class I HLA-A, -B, -C antigens are expressed ubiquitously on nucleated cells, whereas the class II HLA-DR, -DQ, -DP antigens are normally expressed on B cells, monocytes, macrophage, dendritic cells and on activated T cells. HLA typing identifies the unique constellation of HLA antigens for an individual. Tests of HLA-class I (A, B, C) and class II (DR, DQ, DP) gene polymorphisms are integrals for:
The UCLA Immunogenetics Center (UIC) uses DNA-based molecular diagnostic techniques to identify HLA genes. HLA typing using these newer DNA technologies provides tests that are more robust, accurate and reliable in resolving allele-level differences in HLA genes that cannot be detected by serology. Reagents are synthetic, uniform and reproducible. DNA tests can be performed using a variety of source materials (lymphocytes, whole blood, buccal swabs, biopsy samples, frozen tissue) and are less affected by viability and sample age.
Several approaches to HLA typing are used, offering a range of typing resolution levels from low (antigen-level) to high (allele-level). Tests used to identify HLA types rely on amplification of limited stretches of genomic DNA within the HLA genes. The genetic polymorphisms associated with the different HLA alleles are identified through hybridization with specific amplification primers (SSP) or probes (SSO) or by direct sequencing-based typing (SBT).
Reverse SSO hybridization is used to determine HLA-A, -B, -C, -DR, -DQ and -DP locus types at an intermediate and higher than intermediate levelsof resolution. Tests of this type are used when low or intermediate resolution typing is required or as a screening test to identify potential donors or individuals who may later require higher resolution testing.
This technology is used for high volume testing and allows for relatively low-cost typing for bone marrow donor drives or other applications involving large sample numbers. Special volume pricing and terms may apply.
PCR-SSP is also used to determine HLA-A, -B, -C, -DR and DQ locus types at a resolution similar to serological testing. PCR-SSP is a very rapid test that can be performed in 3-4 hours from the time a sample is received. PCR-SSP is used for typing deceased organ donors when speed is an important consideration. PCR-SSP can also be used to provide higher resolution testing and may be employed to resolve alleles.
SBT provides the highest resolution HLA typing for HLA-A, -B, -C, -DR, -DQ and -DP locus alleles. SBT is used when the highest resolution typing is important as in donors and recipients of stem cell transplants or in examining disease associations.