tissue typing

Tissue Typing 

Definition

Tissue typing is a group of procedures that determines the type of histocompatibility antigens on a person's cells or tissues. This procedure is typically used prior to transplantation of tissues or organs.

Purpose

Tissue typing is done prior to transplantation to ensure as close a match as possible between the donor and the recipient. If the histocompatibility antigens do not match well, there is a much greater chance that the recipient will reject the donated tissue.

Histocompatibility antigens are molecules on the surface of all cells in the body. The specific types of histocompatibility antigens present on a person's cells determine their identity and distinguish each person. They are a "fingerprint."

Each person has a unique set of histocompatibility antigens. If the antigens on tissue or organs from a donor do not match that of the recipient, a rejection response can occur. The recipient's immune system will detect the difference between the two sets of antigen and start a rejection response to kill the donated tissue. Except in the case of identical twins, no two people are identical in terms of their histocompatibility antigen types. However, the closer two tissues come to matching, the more likely the recipient will accept the donated tissue or organ.

Human Lymphocyte Antigens (HLA) is the name given to the most commonly used histocompatibility antigens. The antigens can be grouped into two classes: class I antigens are found on almost all cells, and class II antigens are normally found only on B lymphocytes, macrophages, monocytes, dendritic cells, and endothelial cells.

Description

Generally, typing is performed on blood cells because they are an easy sample to obtain. Blood is withdrawn from a vein in the forearm, and the cells are separated. There are a number of different techniques used to identify the antigens on the cells. Typically, specific antibodies react with the cells. Each antibody preparation is specific for one histocompatibility antigen. If the antigen is present, the antibody will bind to it. Laboratory instruments are used to detect antibody binding to the cells. Class II antigens are determined by the mixed lymphocyte reaction (MLR) or by a polymerase chain reaction (PCR). In the mixed lymphocyte reaction, lymphocyte replication occurs if there is a mismatch, and is detected by a specific assay. The PCR test is a new DNA-based test that can detect the presence or absence of antigens by determining whether cells have the genes for the antigens.

One type of transplant does not require tissue typing. In the case of corneal transplants, tissue typing is not needed because cornea do not have their own blood supply. This greatly reduces the chance that immune cells will come in contact with the cornea and recognize it as foreign. For this reason, corneas can be transplant from any person, and there is little chance of rejection.

Normal results

Because each person has their own histocompatibility antigen "fingerprint," there is no true normal result. Each fingerprint is unique.

Resources

Books

Berkow, Robert, editor. Merck Manual of Medical Information. Whitehouse Station, NJ: Merck Research Laboratories, 1997.

Key terms

Antibody — A molecule produced by the body that is part of the immune response to attack antigens.

Antigen — A molecule that causes the body to produce an immunological response to attack the antigen.

Cornea — The transparent outer layer of the eye. It covers the iris and lens.

Lymphocyte — A class of white blood cells that are responsible for creating the immune response to antigens.

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tissue typing,

a systematized series of tests to evaluate the intraspecies compatibility of tissues from a donor and a recipient before transplantation. Typing is accomplished by identifying and comparing a large series of human leukocyte antigens in the cells of the body. See also immune system, transplant.

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tissue typing,

n a systematic sequence of tests used to determine the compatibility between a recipient and a donor before transplantation; typing is done by identification and comparison of a series of human leukocyte antigens present in the cells.

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tissue

a group or layer of similarly specialized cells that together perform certain special functions. For anatomically specific tissues see under their identifying titles, e.g. adipose, connective.

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tissue death

see necrosis.

tissue density

the penetrability of tissue by x-rays, bone and tooth being most dense, blood and soft tissue the next, fat the next, and gas and air least.

tissue edema

an abnormal accumulation of tissue fluid.

tissue factor

see tissue thromboplastin.

tissue fluid

the extracellular fluid that constitutes the environment of the body cells. It is low in protein, is formed by filtration through the capillaries, and the excess drains away as lymph. See also interstitial fluid.

tissue inhibitors

inhibitors of fibrinolysis; present in placenta.

indifferent tissue

undifferentiated embryonic tissue.

tissue necrosis fever

fever caused by pyrogens released by necrotic pyrogens.

tissue plasminogen activator

see plasminogen activator.

tissue reacting agent

substances that have a poorly defined but advantageous local effect on tissues.

tissue receptor site

a cell receptor common to cells of a particular tissue.

tissue residue

residues of chemical substances that are unacceptable to local pure food legislation especially sulfonamides, estrogens, chlorinated hydrocarbons, heavy metals. These are thought or known to have a deleterious effect on people eating or drinking the relevant animal product. See also chemical food residue.

tissue sensitivity

the susceptibility of individual tissues to injury by x-ray. The injury may be by way of inflammation, necrosis or cessation of cell growth. Fast-growing tissues in which the cells have a high mitotic index are the most sensitive, especially gonads, germinative layer of skin and erythropoietic tissues.

supportive t's

cartilage and bone.

tissue therapy

see glandular therapy.

tissue typing

identification of tissue types for purposes of predicting acceptance or rejection of grafts and organ transplants. The process and purposes of tissue typing are essentially the same as for blood typing. The major difference lies in the kinds of antigens being evaluated. White blood cells, particularly lymphocytes, are used for tissue typing. The acceptance of allografts depends particularly on the matching of MHC antigens. If the donor and recipient are not MHC identical, the allograft is rejected. See also typing.

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typing

in transplantation and transfusion immunology, a method of measuring the degree of organ, solid tissue, or blood compatibility between two individuals, in which specific histocompatibility antigens (e.g. those present on leukocytes) or other cell surface antigens, e.g. red blood cell antigens, are detected by means of suitable immune serum.

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blood typing

determining the antigenic determinants present on the surface of red blood cells by using specific antibodies (typing serums). See also blood group.

phage typing

see phage typing.

tissue typing

see tissue typing.