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Tissue typing is a procedure in which the tissues of a prospective donor and recipient are tested for compatibility prior to transplantation. Mismatched donor and recipient tissues can lead to rejection of the tissues. There are multiple methods of tissue typing.

Overview

During tissue typing, an individual’s human leukocyte antigens (HLA) are identified. HLA molecules are presented on the surface of cells and facilitate interactions between immune cells (such as dendritic cells and T cells) that lead to adaptive immune responses. If HLA from the donor is recognized by the recipient's immune system as different from the recipient's own HLA, an immune response against the donor tissues can be triggered. More specifically, HLA mismatches between organ donors and recipients can lead to the development of anti-HLA donor-specific antibodies (DSAs). DSAs are strongly associated with the rejection of donor tissues in the recipient, and their presence is considered an indicator of antibody-mediated rejection. When donor and recipient HLA are matched, donor tissues are significantly more likely to be accepted by the recipient's immune system. During tissue typing, a number of HLA genes should be typed in both the donor and recipient, including HLA Class I A, B, and C genes, as well as HLA Class II DRB1, DRB3, DRB4, DRB5, DQA1, DQB1, DPA1, and DPB1 genes. HLA typing is made more difficult by the fact that the HLA region is the most genetically variable region in the human genome.

Methods of Tissue Typing

One method of conducting tissue typing is through serological typing. In this technique, a donor's blood cells are HLA typed by mixing them with serum containing anti-HLA antibodies. If the antibodies recognize their epitope on the donor's HLA then complement activation occurs and results in cell lysis and death, allowing the cells to take up a dye (trypan blue). This allows for identification of the cells' HLA based indirectly on the specificity of the known antibodies in the serum. This method has been used widely since it is simple, quick, and low-cost; however, the huge variability in HLA alleles means that serum containing antibodies specific to the HLA of the cells being tested may not be available. Serological typing does not give a clear picture of the HLA region and does not always result in successful HLA typing.

Recently, other more effective approaches have emerged.

Other methods of tissue typing include sequence-specific primer polymerase chain reaction (PCR), sequence-specific oligonucleotide (SSO) probes, and direct DNA sequencing. The results of these procedures are compared with available published HLA gene sequences to determine the type of HLA.