SEC reveals the profile of the oligomeric species contained in the (A) Tni-, (B) HEK-, (C) Sf9-, (D) Nb-, and (E) Sf9 HAT- derived HA preparations from A/Brisbane/59/07. Likewise, the oligomeric species contained in the Tni-, HEK-, Sf9-, Nb-, and Sf9 HAT- derived HA preparations from B/Florida/04/06 are displayed in panels F-J. Molecular weight standards (dotted line) are included as a reference. Fractions containing monomeric HA elute at volumes that correspond to the 66 kDa standard. HMWO fractions (> 669 kDa) contain aggregates that are composed of at least 9 HA monomers.