epitoopit

Epitoopit are specific parts of an antigen that are recognized by the immune system. In immunology, an epitooppi is the molecular determinant to which antibodies or immune receptors bind after antigen processing. Epitopes can reside on proteins, polysaccharides, or other molecules and determine the specificity of immune responses to pathogens, allergens, and vaccines.

There are two main classes of epitopes: B cell epitopes, which are recognized by antibodies and B cell receptors, and T cell epitopes, which are presented by MHC molecules to T cell receptors. B cell epitopes can be linear, consisting of a continuous amino acid sequence, or conformational, formed by the three‑dimensional folding of a protein. T cell epitopes are short peptides derived from antigens and are presented by MHC class I molecules to CD8+ T cells or by MHC class II molecules to CD4+ T cells. Typical lengths are about 8–11 amino acids for class I and 13–25 amino acids for class II, though there is variation.

Epitopes play a central role in vaccine design, diagnostics, and immunotherapy. Epitope mapping aims to identify the exact positions of epitopes on an antigen, using peptide libraries, phage display, or computational prediction. Some epitopes are immunodominant and drive strong immune responses, while others may be subdominant or tolerogenic. The study of epitopes also informs understanding of cross‑reactivity, autoimmunity, and the development of epitope‑based vaccines that target specific immune responses with minimized side effects.

See also: Antigen, Antibody, MHC, Epitope mapping.