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Epitope
 
 
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An epitope, also known as antigenic determinant, is the part of a macromolecule
Macromolecule

The term macromolecule by definition implies "large molecule". In the context of biochemistry, the term may be applied to the four conventional biopolymers , as well as non-polymeric molecules with large molecular mass such as macrocycles....
 that is recognized by the immune system
Immune system

An immune system is a collection of biological processes within an organism that protects against disease by identifying and killing pathogens and tumour cells....
, specifically by antibodies
Antibody

Antibodies are gamma globulin proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacterium and viruses....
, B cell
B cell

B cells are lymphocytes that play a large role in the humoral immunity . The principal functions of B cells are to make antibody against antigens, perform the role of Antigen Presenting Cells and eventually develop into memory B cells after activation by antigen interaction....
s, or T cell
T cell

T cells belong to a group of white blood cells known as lymphocytes, and play a central role in cell-mediated immunity. They can be distinguished from other lymphocyte types, such as B cells and natural killer cells by the presence of a special receptor on their cell surface called T cell receptors ....
s. The part of an antibody that recognizes the epitope is called a paratope. Although epitopes are usually thought to be derived from nonself proteins, sequences derived from the host that can be recognized are also classified as epitopes.

Most epitopes recognized by antibodies or B cells can be thought of as three-dimensional surface features of an antigen
Antigen

An antigen is a substance that prompts the generation of antibodies and can cause an immune response. The word originated from the notion that they can stimulate antibody generation....
 molecule; these features fit precisely and thus bind to antibodies.






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Encyclopedia


An epitope, also known as antigenic determinant, is the part of a macromolecule
Macromolecule

The term macromolecule by definition implies "large molecule". In the context of biochemistry, the term may be applied to the four conventional biopolymers , as well as non-polymeric molecules with large molecular mass such as macrocycles....
 that is recognized by the immune system
Immune system

An immune system is a collection of biological processes within an organism that protects against disease by identifying and killing pathogens and tumour cells....
, specifically by antibodies
Antibody

Antibodies are gamma globulin proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacterium and viruses....
, B cell
B cell

B cells are lymphocytes that play a large role in the humoral immunity . The principal functions of B cells are to make antibody against antigens, perform the role of Antigen Presenting Cells and eventually develop into memory B cells after activation by antigen interaction....
s, or T cell
T cell

T cells belong to a group of white blood cells known as lymphocytes, and play a central role in cell-mediated immunity. They can be distinguished from other lymphocyte types, such as B cells and natural killer cells by the presence of a special receptor on their cell surface called T cell receptors ....
s. The part of an antibody that recognizes the epitope is called a paratope. Although epitopes are usually thought to be derived from nonself proteins, sequences derived from the host that can be recognized are also classified as epitopes.

Most epitopes recognized by antibodies or B cells can be thought of as three-dimensional surface features of an antigen
Antigen

An antigen is a substance that prompts the generation of antibodies and can cause an immune response. The word originated from the notion that they can stimulate antibody generation....
 molecule; these features fit precisely and thus bind to antibodies. Exceptions are linear epitope
Linear epitope

A linear or a sequential epitope is an epitope that is recognized by antibody by its linear sequence of amino acids, or primary structure. In contrast, most antibodies recognize a conformational epitope that has a specific three-dimensional shape and its protein structure....
s, which are determined by the amino acid
Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
 sequence (the primary structure
Primary structure

In biochemistry, the primary structure of a biological molecule is the exact specification of its atomic composition and the chemical bonds connecting those atoms ....
) rather than by the 3D shape (tertiary structure
Tertiary structure

In biochemistry and chemistry, the tertiary structure of a protein or any other macromolecule is its three-dimensional structure, as defined by the atomic coordinates....
) of a protein.

T cell epitopes are presented on the surface of an antigen-presenting cell
Antigen-presenting cell

An antigen-presenting cell or accessory cell is a Cell that displays foreign antigen complexed with Major histocompatibility complex on its surface....
, where they are bound to MHC
Major histocompatibility complex

The major histocompatibility complex is a large genome region or gene family found in most vertebrates. It is the most gene-dense region of the mammalian genome and plays an important role in the immune system, autoimmunity, and reproduction success....
 molecules. T cell epitopes presented by MHC class I molecules are typically peptides between 8 and 11 amino acids in lengths, whereas MHC class II molecules present longer peptides, and non-classical MHC molecules also present non-peptidic epitopes such as glycolipids.

Epitopes can be mapped using protein microarray
Protein microarray

A protein microarray, sometimes referred to as a protein binding microarray,provides a multiplex approach to identify protein-protein interactions, to identify the substrates of protein kinases, or to identify the targets of biologically active small molecules....
s, and with the ELISPOT
ELISPOT

The Enzyme-linked immunosorbent spot assay is a common method for monitoring immune responses in humans and animals. It was developed by Cecil Czerkinsky in 1983....
 or ELISA
ELISA

Enzyme-Linked ImmunoSorbent Assay, also called ELISA, Enzyme ImmunoAssay or EIA, is a biochemistry technique used mainly in immunology to detect the presence of an antibody or an antigen in a sample....
 techniques.

Genetic sequences coding for epitopes that are recognised by common antibodies can be fused to genes, thus aiding further molecular characterization of the gene product. Common epitopes used for this purpose are c-myc, HA, FLAG, V5.

Epitopes are sometimes cross-reactive. This property is exploited by the immune system in regulation by anti-idiotypic antibodies (originally proposed by Nobel laureate Niels Kaj Jerne
Niels Kaj Jerne

Niels Kaj Jerne, Fellow_of_the_Royal_Society was a Denmark immunologist. He was awarded the Nobel Prize in Physiology or Medicine in 1984. The citation read "For theories concerning the specificity in development and control of the immune system and the discovery of the principle for production of monoclonal antibodies"....
). If an antibody binds to an antigen's epitope, the paratope could become the epitope for another antibody that will then bind to it. If this second antibody is of IgM class, its binding can upregulate the immune response; if the second antibody is of IgG class, its binding can downregulate the immune response.

Intensive research is currently taking place to design reliable tools that will predict epitopes on proteins.

See also

  • Mimotope
    Mimotope

    A mimotope is a macromolecule, often a peptide, which mimics the structure of an epitope. Because of this property it causes an antibody response identical to the one elicited by the epitope....
  • Epitope mapping
    Epitope mapping

    Epitope mapping is the process of identification and characterization of the minimum molecular structures that are able to be recognized by the Immune System elements, mainly T and B cells....
  • Linear epitope
    Linear epitope

    A linear or a sequential epitope is an epitope that is recognized by antibody by its linear sequence of amino acids, or primary structure. In contrast, most antibodies recognize a conformational epitope that has a specific three-dimensional shape and its protein structure....
  • Conformational epitope
    Conformational epitope

    A conformational epitope is a sequence of subunits composing an antigen that come in direct contact with a receptor of the immune system.An antigen is any substance that the immune system can recognize as foreign....
  • Polyclonal B cell response
    Polyclonal B cell response

    Polyclonal B cell response is a natural mode of immune response exhibited by the adaptive immune system of mammals. It ensures that a single antigen is recognized and attacked through its overlapping parts, called epitopes, by multiple Clone of B cell....
  • Odotope


Epitope databases



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