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We can define an Epitope as a molecular area over the surface of an antigen either B-cell or T-cell, which evokes an immune response of integrating with a specific antibody, resulting in antibody production. It is a protein segment that happens to be four to five amino acids long. Here, a particular or a distinct antigen will bind itself with the long segment. The purpose of an Epitope is to develop an immune response to a raiding pathogen.
Body:
Epitopes are further referred to as ‘Antigenic Determinants” as they are the authentic part of an antigen that decides the response of the immune system. These proteins are mainly polysaccharides and glycoproteins. Our immune system recognizes these antigens by identifying 3-D shapes also known as the “Epitopes”. A solo protein antigen may contain different kinds of epitopes where they bind with particular antibodies or T-cell receptors.
Types of an Epitope:
Based on their structures, epitopes can be classified as follows:
Linear Epitopes.
Conformational Epitopes.
Linear Epitopes:
• It is found in most of the polysaccharides, grainy proteins, and one-stranded nucleic acids.
• It is composed of adjoining amino acid residues in coordinate bonds.
• It depends on a linear structure or format of almost 6 amino acids.
• Availability of modification of protein substances.
Conformational Epitopes:
• It is found in most of the globular proteins and other local nucleic acids.
• It is composed of amino acid residues which are brought close to each other through folding.
• It depends on the 3-D structure.
• Linked with local proteins.
T-Cell Epitopes:
T-Cells epitopes are the peptides that are derived from the antigen bodies and are recognized by the T-cell receptor. They are bound to the MHC molecules which can be found on the cell surface of APCs. We can identify T-Cells through the below-listed points:
1. Binding of the peptides with the MHC molecules of class I.
2. Binding of peptides with the MHC molecules of class II.
3. Tepitool.
4. The combination of MHC Class I molecules + TAP transport + Proteasomal cleavage.
T-cell receptors cannot bind to the free peptide or antigens.
T-cell epitopes may contain hydrophobic amino acids sequences and can also be termed as “internal epitopes”.
The T-Cell epitopes are carried out with the help of MHC multimers and lymphoproliferation or through ELISPOT essays. Prediction of a T-Cell epitope aims to identify the shortest peptides in an antigen which are therefore capable of stimulation of either CD4+ or CD8+ T-Cells. Thus, the above capability to stimulate T-Cells is called immunogenicity. The T-cell epitopes immunogenicity is determined or based on these following steps:
Processing of Antigen.
The binding of the peptide to the MHC molecules.
TCR recognition.
However, a critical issue with the prediction of T-cell epitopes with the help of the peptide-MHC binding models is the MHC polymorphism.
Conclusion:
Thus, the epitopes are useful in making vaccines. For example, the first vaccine which was based on epitope was introduced in 1985 by Jacob et al. The vaccines help in stimulating humoral as well as cellular immune responses with the support of B-Cell or T-cell epitopes. Hence, epitopes play an important role in stimulating response within the antibodies which helps us defend against harmful pathogens affecting our body. It is an important part of the study of the Immunology discipline.
