Антидене байланысатын антигеннің бөлігі - Эпитоптар туралы

Chemical entity which can be bound by an antibody
An epitope, also known as antigenic determinant, is the part of an antigen that is recognized by the immune system, specifically by antibodies, B cells, or T cells. The part of an antibody that binds to the epitope is called a paratope. Although epitopes are usually non self proteins, sequences derived from the host that can be recognized (as in the case of autoimmune diseases) are also epitopes. The epitopes of protein antigens are divided into two categories, conformational epitopes and linear epitopes, based on their structure and interaction with the paratope. Conformational and linear epitopes interact with the paratope based on the 3 D conformation adopted by the epitope, which is determined by the surface features of the involved epitope residues and the shape or tertiary structure of other segments of the antigen. A conformational epitope is formed by the 3 D conformation adopted by the interaction of discontiguous amino acid residues. In contrast, a linear epitope is formed by the 3 D conformation adopted by the interaction of contiguous amino acid residues. A linear epitope is not determined solely by the primary structure of the involved amino acids. Residues that flank such amino acid residues, as well as more distant amino acid residues of the antigen affect the ability of the primary structure residues to adopt the epitope's 3 D conformation. 90% of epitopes are conformational.

T cell epitopes are presented on the surface of an antigen presenting cell, where they are bound to major histocompatibility complex (MHC) molecules. In humans, professional antigen presenting cells are specialized to present MHC class II peptides, whereas most nucleated somatic cells present MHC class I peptides. T cell epitopes presented by MHC class I molecules are typically peptides between 8 and 11 amino acids in length, whereas MHC class II molecules present longer peptides, 13–17 amino acids in length, and non classical MHC molecules also present non peptidic epitopes such as glycolipids.

The part of the antigen that immunoglobulin or antibodies bind to is called a B cell epitope. B cell epitopes can be divided into two groups: conformational or linear. There are additional epitope types when the quaternary structure is considered. although not all in silico T cell epitope prediction algorithms are equivalent in their accuracy. There are two main methods of predicting peptide MHC binding: data driven and structure based.

There are two main methods of epitope mapping: either structural or functional studies. Methods for structurally mapping epitopes include X ray crystallography, nuclear magnetic resonance, and electron microscopy. Mutagenesis uses randomly/site directed mutations at individual residues to map epitopes.

Epitopes are often used in proteomics and the study of other gene products. Using recombinant DNA techniques genetic sequences coding for epitopes that are recognized by common antibodies can be fused to the gene. Following synthesis, the resulting epitope tag allows the antibody to find the protein or other gene product enabling lab techniques for localisation, purification, and further molecular characterization. Common epitopes used for this purpose are Myc tag, HA tag, FLAG tag, GST tag, 6xHis, V5 tag and OLLAS. Peptides can also be bound by proteins that form covalent bonds to the peptide, allowing irreversible immobilisation. These strategies have also been successfully applied to the development of "epitope focused" vaccine design.

The first epitope based vaccine was developed in 1985 by Jacob et al. Epitope based vaccines stimulate humoral and cellular immune responses using isolated B cell or T cell epitopes. Neoantigens are often associated with tumor antigens and are found in oncogenic cells. Neoantigens and, by extension, neoantigenic determinants can be formed when a protein undergoes further modification within a biochemical pathway such as glycosylation, phosphorylation or proteolysis. This, by altering the structure of the protein, can produce new epitopes that are called neoantigenic determinants as they give rise to new antigenic determinants. Recognition requires separate, specific antibodies.