Epitopi

Epitopi, or epitopes in English, are the specific parts of an antigen that are recognized by the adaptive immune system. They are typically small molecular features on macromolecules such as proteins, polysaccharides, lipids, or nucleic acids. Epitopi serve as binding sites for immune receptors, including antibodies produced by B cells and T cell receptors in conjunction with MHC molecules.

There are two main classes: B cell epitopi, which bind antibodies, and T cell epitopi, which are recognized when peptides are presented by MHC molecules on antigen-presenting cells. B cell epitopi can be linear, consisting of a contiguous stretch of amino acids, or conformational (discontinuous), formed by amino acids brought together in the folded protein. T cell epitopi are typically linear peptides derived from antigen processing.

Properties and determinants include surface exposure on the native antigen, which facilitates recognition. Immunodominance describes why certain epitopi evoke stronger immune responses. Modifications such as glycosylation, sequence variation, or conformational changes can alter epitope recognition. Epitopi can also cross-react with related antigens or generate neoepitopes in disease states.

Size is context-dependent: B cell linear epitopi are commonly about 5–20 amino acids long; conformational epitopi are defined by the three-dimensional arrangement of residues, not by a fixed length. Mapping and identification employ overlapping peptide libraries, phage display, peptide microarrays, alanine scanning, and structural methods like X-ray crystallography or cryo-electron microscopy. Computational prediction methods exist but have limited accuracy.

Applications include epitope-based vaccines that focus responses on protective regions, diagnostic assays targeting specific epitope antibodies, therapeutic antibodies, and immune monitoring. In different languages, epitopi is the plural form; in English, epitopes is used. See also antigen, immunogenicity, MHC, antibody, T cell receptor.