Figure 1.

Structure of the influenza hemagglutinin (HA), with major domains. The structure shown is based on x-ray crystallographic studies of the trimeric soluble 1918 H1N1 influenza HA protein (PDB ID: 1RUZ). The structure contains a globular head domain that is the target for antibodies that bind to the receptor-binding domain and, rarely, the vestigial esterase domain. The stem region is more conserved and binds different classes of antibodies. General characteristics and inhibitory mechanisms of domain-specific human monoclonal antibodies are indicated.