Histocompatibility
Encyclopedia
Histocompatibility is the property of having the same, or mostly the same, allele
s of a set of gene
s called the major histocompatibility complex
. These genes are expressed in most tissues as antigen
s, to which the immune system
makes antibodies
. The immune system at first makes antibodies to all sorts of antigens, including those it has never been exposed to, but stops making them to antigens present in the body. If the body is exposed to foreign antigens, as by getting a tissue graft
, it attacks the foreign material unless it is histocompatible.
A similar system exists in many plant
s; its purpose is not to reject grafts, but to prevent inbreeding
. Pollen from a plant sharing a histocompatibility gene with the female either fails to grow or dies soon after germinating.
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
s of a set of gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s called the major histocompatibility complex
Major histocompatibility complex
Major histocompatibility complex is a cell surface molecule encoded by a large gene family in all vertebrates. MHC molecules mediate interactions of leukocytes, also called white blood cells , which are immune cells, with other leukocytes or body cells...
. These genes are expressed in most tissues as antigen
Antigen
An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...
s, to which the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
makes antibodies
Antibody
An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...
. The immune system at first makes antibodies to all sorts of antigens, including those it has never been exposed to, but stops making them to antigens present in the body. If the body is exposed to foreign antigens, as by getting a tissue graft
Medical grafting
Grafting refers to a surgical procedure to move tissue from one site to another on the body, or from another person, without bringing its own blood supply with it. Instead, a new blood supply grows in after it is placed. A similar technique where tissue is transferred with the blood supply intact...
, it attacks the foreign material unless it is histocompatible.
A similar system exists in many plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s; its purpose is not to reject grafts, but to prevent inbreeding
Inbreeding
Inbreeding is the reproduction from the mating of two genetically related parents. Inbreeding results in increased homozygosity, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is...
. Pollen from a plant sharing a histocompatibility gene with the female either fails to grow or dies soon after germinating.
See also
- Transplant rejectionTransplant rejectionTransplant rejection occurs when transplanted tissue is rejected by the recipient's immune system, which destroys the transplanted tissue. Transplant rejection can be lessened by determining the molecular similitude between donor and recipient and by use of immunosuppressant drugs after...
- Tissue typingTissue typingTissue typing is a procedure in which the tissues of a prospective donor and recipient are tested for compatibility prior to transplantation. An embryo can be tissue typed to ensure that the embryo implanted can be a cord-blood stem cell donor for a sick sibling.One technique of tissue typing,...
- Major histocompatibility complex (MHC)Major histocompatibility complexMajor histocompatibility complex is a cell surface molecule encoded by a large gene family in all vertebrates. MHC molecules mediate interactions of leukocytes, also called white blood cells , which are immune cells, with other leukocytes or body cells...
- Clonal selection theory