C-terminal 6x His-tagged influenza hemagglutinin HA(ΔTM) (H3N2) (A/Perth/16/2009) protein (a.a.18-529) (GenBank Accession# ACS71642). Over 95% are trimeric fraction collected from column chromatography. A trimerization domain sequence has been introduced into the C-terminal of HA to stabilize the formation of trimer HA.