Antigenic determinants of influenza virus haemagglutinin. X. A comparison of the physical and antigenic properties of monomeric and trimeric forms.

Haemagglutinin prepared from influenza virus A/Memphis/1/71 by bromelain digestion was centrifuged through continuous sucrose gradients buffered at pH 7.4 or pH 4.9. From these gradients were isolated two forms of the protein which displayed different equilibrium sedimentation properties. One species behaved as a molecule with a mol. wt. of 190 000, the other with a mol. wt. of 70 000. These results are consistent with the separation of trimeric and monomeric haemagglutinin. A comparison of their antigenic properties, using monoclonal antibodies raised against intact virus, showed that major antigenic differences occur between the two forms of haemagglutinin. None of the monoclonal antibodies reacted with haemagglutinin denatured by reduction and alkylation.