Tissue typing

A method used to match organ and tissue transplant recipients with compatible donors

Tissue typing is a critical process in the field of transplantation medicine that involves testing the compatibility of tissue between a donor and a recipient. This process is essential to ensure the success of organ transplantation and to minimize the risk of graft rejection.

Overview

Tissue typing is primarily concerned with the identification of human leukocyte antigens (HLA) on the surface of cells. These antigens play a crucial role in the immune system's ability to distinguish between self and non-self. The closer the HLA match between donor and recipient, the lower the risk of rejection.

Human Leukocyte Antigens (HLA)

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Diagram of HLA-DRB1, a type of HLA molecule.

HLAs are proteins found on the surface of most cells in the human body. They are encoded by genes located on chromosome 6 and are highly polymorphic, meaning there is a great variety of HLA types in the human population. The main classes of HLA relevant to tissue typing are:

• Class I HLAs: These include HLA-A, HLA-B, and HLA-C. They are present on almost all nucleated cells and are important for presenting peptides to cytotoxic T cells.
• Class II HLAs: These include HLA-DR, HLA-DQ, and HLA-DP. They are primarily found on antigen-presenting cells such as macrophages, dendritic cells, and B cells.

Methods of Tissue Typing

Several methods are used to determine HLA compatibility:

Serological Testing

This traditional method involves mixing recipient serum with donor lymphocytes and observing for a reaction. It is based on the principle of complement-dependent cytotoxicity.

Molecular Typing

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DNA sequencing is a modern method used in tissue typing.

Modern techniques involve DNA sequencing to identify HLA alleles. This method is more precise and can detect even minor differences in HLA genes.

Crossmatching

Crossmatching tests the recipient's serum against donor cells to check for pre-existing antibodies that might cause rejection. A positive crossmatch indicates a high risk of rejection.

Importance in Transplantation

Tissue typing is crucial for the success of kidney transplantation, liver transplantation, heart transplantation, and bone marrow transplantation. A good HLA match can significantly improve graft survival rates and reduce the need for immunosuppressive therapy.

Challenges and Future Directions

Despite advances in tissue typing, challenges remain, such as the limited availability of perfectly matched donors and the complexity of the HLA system. Research is ongoing to improve matching techniques and to develop tolerance induction strategies that could allow for successful transplantation with less stringent matching.

Related pages

• Organ transplantation
• Immunology
• Graft rejection
• Bone marrow transplantation