Peptidantigen

Peptidantigen is a term used to describe a peptide that can function as an antigen in the immune system. It refers to a short amino acid sequence derived from a protein that is recognized by T or B cells when presented in the context of major histocompatibility complex (MHC) molecules.

Peptidantigens are generated by proteolytic processing of proteins in antigen-presenting cells; cytosolic proteins are degraded by the proteasome, peptides transported into the endoplasmic reticulum by TAP and loaded on MHC class I for presentation to CD8+ T cells. Exogenous or endosomal proteins are processed in endosomes and loaded onto MHC class II for presentation to CD4+ T cells.

Some peptidantigens are self-derived and can contribute to autoimmunity if tolerance fails; others originate from pathogens or tumors and are exploited in vaccines and cancer immunotherapies.

The immunogenicity of a peptidantigen depends on its binding affinity to the presenting MHC molecule, its processing efficiency, and recognition by T cell receptors. Typical lengths are about 8–11 amino acids for MHC class I and 13–25 amino acids for MHC class II; peptides must also be compatible with the binding motifs of the relevant MHC molecule.

In clinical and research settings, synthetic peptidantigens are used to map T cell epitopes, design peptide-based vaccines, or monitor immune responses. Peptidantigen concepts also inform studies of autoimmunity, infectious diseases, and tumor immunology.