OVA 323–339 (ISQAVHAAHAEINEAGR) is a 17–amino acid peptide from chicken Ovalbumin. It is a well-known CD4⁺ T-cell epitope presented by MHC class II molecules to activate helper T cells. This peptide is widely used in mice to study antigen-specific T-cell responses and immune regulation, including models of allergy and autoimmunity. Its defined sequence and reproducible immunogenicity make it a common tool in immunology research.