Antigenpeptide

An antigenpeptide is a short peptide fragment that can act as an antigen, capable of being recognized by the adaptive immune system. Such peptides are commonly termed epitopes when they are recognized by T cells or by B cell receptors, and may arise from a pathogen, tumor protein, or the host proteome.

Most antigen peptides are generated through cellular processing. Intracellular proteins are degraded by the proteasome into short peptides that are transported into the endoplasmic reticulum by TAP and loaded onto MHC class I molecules, which present them on the cell surface to CD8+ T cells. Extracellular proteins are endocytosed, processed in lysosomes, and loaded onto MHC class II for presentation to CD4+ T cells.

B cell recognition can involve native or processed peptides, especially when they form accessible epitopes on protein surfaces. Synthetic antigen peptides are widely used in research for epitope mapping, diagnostic assays, and peptide-based vaccines. The immunogenicity of a peptide depends on MHC binding affinity, the T cell repertoire, peptide stability, and the use of adjuvants.

Because MHC is highly polymorphic, different individuals present different antigenpeptides. This variability, along with tolerance mechanisms and potential for cross-reactivity, influences vaccine design and immune monitoring. In practice, the term is often used interchangeably with epitope or peptide antigen, with typical lengths of about 8–11 residues for MHC I and 12–25 for MHC II.