Influenza NP (311-325) is a biologically active peptide consisting of amino acids 311 to 325 from the influenza virus nucleoprotein (NP). As a bona fide MHC class II-restricted epitope, it is critical for studying host immune responses during viral infection, inducing robust gamma interferon (IFN-gamma) production in intracellular cytokine assays without stimulating CD8 T-cells in mice. The presence of Glutamine (Q) or Glutamic acid (E) at the N-terminus can lead to spontaneous formation of Pyroglutamyl (pGlu) peptides, enhancing peptide stability against gastrointestinal proteases. These peptides are considered a normal variant and included in peptide purity measurements in HPLC analysis.