Membrane fusion by surrogate receptor-bound influenza haemagglutinin

In influenza infections, haemagglutinin (HA) mediates the fusion of virus a nd cellular membranes at endosomal pH, between pH 5 and 6. In vitro, when r econstituted into virosomes, efficient fusion requires target membranes to contain sialic acid receptors or receptor analogues. In the experiments rep orted, lipid-associated anti-HA monoclonal Fab' fragments were used as surr ogate receptors to investigate the fusion capacity of receptor-bound HA com pared with unbound HA. The conclusions are drawn, in contrast to those from previous studies, that bound HA can mediate fusion and that fusion mainly involves bound HA when the liposome targets are densely packed with surroga te receptors. (C) 1999 Academic Press.