Stanford Synchrotron Radiation Lightsource
Date Published: May 28, 2010

Structural Basis for Senior Immunity to the Current H1N1 Flu
summary written by Raven Hanna

An unusual property of the last year's H1N1 "swine flu" virus pandemic is that it disproportionately affected the young. People over the age of around 65 showed much less vulnerability than to more typical flu strains, suggesting that they might have been exposed to a similar virus over three decades ago. Another atypical property of the 2009 H1N1 strain is that its hemagglutinin (HA) subunit is the same subtype as the regular seasonal strains, whereas most pandemics are caused by viruses with novel HA domains. The HA protein extends out of the virus surface and is responsible for binding the virus to the cell it will infect. Because it is located on the surface of the virus, HA is often targeted by antibodies.

A group of researchers led by Prof. Ian Wilson of The Scripps Research Institute has found structural similarity between last year's H1N1 strain and the 1918 influenza virus that also caused a pandemic. They used SSRL Beam Line 9-2 to solve the 3D structure of the HA subunit of the 2009 H1N1 virus to 2.6 Å resolution. They compared their structure of HA of historic H1 flu strains from 1918 to the present. Their analysis shows a striking similarity between the surface residues in their HA structure and those of the 1918 virus, with decreasing similarity of viruses in subsequent years and a significant drop in similarity around 1940. The researchers also solved a 2.8 Å crystal structure of the 1918 HA bound to an antibody, which shows that the region that is conserved between the 2009 and 1918 strains matches the area recognized by the immune system.

The authors conclude that the resistance of older people to the current H1N1 virus is likely due to antibodies they acquired from flu strains in the early 20th century.

To learn more about this research see the full Scientific Highlight

R. Xu, D. C. Ekiert, J. C. Krause, R. Hai, J. E. Crowe, Jr. and I. A. Wilson, "Structural Basis of Preexisting Immunity to the 2009 H1N1 Pandemic Influenza Virus", Science 328, 357 (2010) doi: 10.1126/science.1186430

SLAC National Accelerator Laboratory
Stanford University