This set of models demonstrates the region-specific properties of antibodies generated from different flu vaccines. Hemagglutinin (HA) is a glycoprotein on the surface of the influenza virus. It binds to a receptor on the host cell, causing the host cell to take in the virus. There are over a dozen HA subtypes, the most common in humans are H1, H2, and H3. There are two HA subtypes in this entry: H1 (pink) and H3 (blue). The colored areas on the outside of the receptors indicate the receptor-binding sites. Broadly-neutralizing antibodies (bnAbs) bind to these regions to block entry to the host cell.

Because HA is the major target for host antibodies, small mutations over time (antigenic drift) allow the virus to escape seasonal immunity. The head region of HA is most subject to mutation. The purple (CH65) and orange (F005) antibodies specifically bind to H1 and H3, respectively.

The stem region of HA is less subject to mutation, so the yellow antibody (FI6) will bind at the stem region of receptors on both flu strains.

H1 protein and CH65 models were created from PDB entry 5UGY; H3 was created from 4WE8. PDB files for F005 and FI6 were provided by the lab of Dr. Barney Graham at the NIAID Vaccine Research Center.