Anti-HA tag antibodies are directed against HA tag, which is derived from the human influenza hemagglutinin protein and is composed of a 10-amino acid peptide sequence, YPYDVPDYA. Anti-HA tag antibodies are directed against the HA tag, which is derived from the human influenza hemagglutinin protein and is composed of a 10-amino acid peptide sequence, YPYDVPDYA. It is a common epitope tag in expression vectors as it does not seem to affect the activity or distribution of the recombinant protein. It has been noted to be cleaved by caspases -3 and -7 and may not be suitable for use in apoptotic cells. The resulting antibodies may be useful in the detection of HA-tagged proteins.