Hemagglutinin (HA) refers to a red blood cell agglutinin. Hemagglutinin is immunogenic, and anti-hemagglutinin antibodies can neutralize it. The HA tag is a short peptide sequence derived from amino acids 98-106 of the human influenza virus hemagglutinin protein, with the amino acid sequence YPYDVPDYA. The molecular weight of the HA tag is approximately 1.1 kDa, making it one of the most widely used tags. By using recombinant DNA technology to fuse the HA tag to the C-terminus or N-terminus of a target protein, it facilitates the purification and detection of the target protein. Antibodies against the HA tag enable precise detection and purification of HA-tagged fusion proteins. Horseradish Peroxidase (HRP) is conjugated to the anti-HA antibody through a specific process. In Western blot (WB) experiments, upon adding chemiluminescent substratesAand B (typically luminol and hydrogen peroxide), the luminol reacts with hydrogen peroxide under the catalytic action of HRP to form an unstable peroxide intermediate. This intermediate decomposes, generating an electronically excited species. When this species returns to the ground state, light is emitted, allowing for rapid detection of the HA-tagged fusion protein.