(Image source-Ref-1) Properties Linear epitopes Conformational epitopes Location Most polysaccharides, fibrilar proteins, and single-stranded nucleic acids. Linear B-cell epitopes (a) are composed of sequential/continuous residues, while conformational B-cell epitopes (b) contain scattered/discontinuous residues along the sequence. Conformational epitopes Linear and conformational B-cell epitopes.The antigenic determinants (epitopes) are divided into two categories based on their structures and interaction with the paratope. B-cell (left) and T-cell (right) epitope recognition (Image source-Ref-1) Properties Recognized by B cells and Antibodies Recognized by T cells Composition Proteins, glycoproteins, polysaccharides, nucleic acids Proteins Configuration Linear/conformational determinants Linear determinants Size 4-8 residues 8-15 residues Number Limited, located on the exposed surface of the antigen Limited to those proteins that can be processed and bind to MHC Types of Epitopes Meanwhile, primed CD4 T-cells become helper (Th) or regulatory (Treg) T-cells. T-cells become cytotoxic T lymphocytes (CTL) following T CD8 epitope recognition. Subsequently, there are CD8 and CD4 T-cell epitopes. T-cell epitopes are presented by class I (MHC I) and II (MHC II) MHC molecules that are recognized by two distinct subsets of T-cells, CD8, and CD4 T-cells, respectively. Thus, each branch of the immune system uniquely suited to recognize antigen in a different environment. As T cells recognize only the processed peptides, those epitopes may be located on those regions (e.g., internal proteins) which are inaccessible to B-cells. The cell-mediated branch (T cells) recognizes protein epitopes (also referred to as T-cell epitopes) displayed together with MHC molecules on self-cells, including altered self-cells such as virus-infected self-cells and cancerous cells. Plasma cells produce large amounts of antibody specific for the epitope recognized by their immunoglobulin receptor. When B cells are exposed to T-dependent antigens, they get activated and undergo class switching, affinity maturation, and differentiate into plasma cells. The humoral branch (B cells) recognizes an enormous variety of epitopes (also referred to as B-cell epitopes): those displayed on the exposed regions of bacteria or viral particles, as well as those displayed on soluble proteins, glycoproteins, polysaccharides, or lipopolysaccharides that have been released from invading pathogens. Identification of Epitopes Functions of EpitopesĮpitope recognition by B-cell and T-cell is central to humoral and cell-mediated immune response.Related antigens are also referred to as cross-reacting antigens because antibodies targeted to one antigen are able to react with all other antigens carrying the same epitope. Related antigens have some epitopes in common but some that are different. There may be a presence of related antigens across various species.
In general, antibodies bind epitopes that are roughly five amino acids or sugars in size, whereas T-cell receptors bind epitopes between 8 and 17 amino acids in size. Most antigens have many determinants (i.e., they are multivalent). This paratope is only capable of binding with one unique epitope.ī cells can recognize an epitope alone but T cells can recognize an epitope only when it is associated with an MHC molecule on the surface of a self-cell (either an antigen-presenting cell or an altered self-cell).Īn antigen can have one or more epitopes. Paratope is located at the tip of the variable region of an immunoglobulin, in its antigen-binding site. The part of an immunoglobulin that binds and fits the epitope is called a paratope. When an antibody binds to an antigen, it isn’t binding to the entire antigen but to a segment of that antigen known as an epitope.
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