Basis of Self and Nonself Recognition
Basis of Self and Nonself
Recognition
Major Histocompatibility Complex
We have known for many years that nonself recognition is very specific. If tissue from one individual is transplanted into another individual of the same species, the graft will grow for a time and then die as immunity against it rises. In the absence of drugs that modify the immune system, tissue grafts will grow successfully only if they are between identical twins or between individuals of highly inbred strains of animals. The molecular basis for this nonself recognition involves certain proteins embedded in the cell surface. These proteins are coded by certain genes, now known as the major histocompatibility complex (MHC). MHC proteins are among the most variable known, and unrelated individuals almost always have different genes. There are two types of MHC proteins: class I and class II. Class I proteins are found on the surface of virtually all cells, whereas class II MHC proteins are found only on certain cells participating in immune responses, such as lymphocytes and macrophages.
The capability of an immune response develops over a period of time in the early development of the organism. All substances present at the time the capacity develops are recognized as self in later life. Unfortunately, the system of self and nonself recognition sometimes breaks down,and an animal may begin to produce antibodies against some part of its own body. This condition leads to one of several known autoimmune diseases, such as rheumatoid arthritis, multiple sclerosis, lupus, and insulin-dependent diabetes mellitus.
Major Histocompatibility Complex
We have known for many years that nonself recognition is very specific. If tissue from one individual is transplanted into another individual of the same species, the graft will grow for a time and then die as immunity against it rises. In the absence of drugs that modify the immune system, tissue grafts will grow successfully only if they are between identical twins or between individuals of highly inbred strains of animals. The molecular basis for this nonself recognition involves certain proteins embedded in the cell surface. These proteins are coded by certain genes, now known as the major histocompatibility complex (MHC). MHC proteins are among the most variable known, and unrelated individuals almost always have different genes. There are two types of MHC proteins: class I and class II. Class I proteins are found on the surface of virtually all cells, whereas class II MHC proteins are found only on certain cells participating in immune responses, such as lymphocytes and macrophages.
The capability of an immune response develops over a period of time in the early development of the organism. All substances present at the time the capacity develops are recognized as self in later life. Unfortunately, the system of self and nonself recognition sometimes breaks down,and an animal may begin to produce antibodies against some part of its own body. This condition leads to one of several known autoimmune diseases, such as rheumatoid arthritis, multiple sclerosis, lupus, and insulin-dependent diabetes mellitus.
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