epitopit

Epitopit, or epitopes, are the specific parts of an antigen that are recognized by the immune system, typically by antibodies or T cell receptors. They are usually small molecular features and can be a short amino acid sequence, a particular surface on a folded protein, or a glycan moiety on a carbohydrate. Epitopes may be linear, formed by a continuous stretch of residues, or conformational, dependent on the three-dimensional folding of the antigen.

B-cell epitopes are accessible on native antigens and may be linear or conformational; they bind antibodies directly. T-cell epitopes are peptides generated through antigen processing and presented by major histocompatibility complex (MHC) molecules to T cell receptors. MHC class I presents to CD8+ T cells with typically 8–11 amino acids, while MHC class II presents to CD4+ T cells with longer peptides.

Epitopes determine the specificity of immune responses and are central to vaccine design and diagnostics. Epitope mapping identifies regions of an antigen that elicit protective or diagnostic responses. Epitope-based vaccines aim to induce focused immunity by including selected epitopes rather than whole pathogens or large proteins.

Identification and characterization approaches include synthetic overlapping peptide libraries, phage display, and mutational analysis. Structural methods such as X-ray crystallography or cryo-electron microscopy can reveal precise antibody–epitope interactions. Computational prediction and high-throughput screens complement experimental mapping, though predictions often require validation.

Practical considerations include variability from antigen diversity and host MHC polymorphism, which influence immunogenicity and cross-reactivity. Epitope information supports development of diagnostics, therapeutic antibodies, and a deeper understanding of autoimmune phenomena driven by molecular mimicry.