Earlier flu viruses provide H1N1 immunity.

• Position: Your Life

A group of immunologically important sites on the H1N1 virus that also are present in seasonal flu viruses that have been circulating for years has been identified by researchers at the University of California, Davis. The molecular sites appear to result in some level of immunity to the new virus.

More than a dozen structural sites, or epitopes, in the virus may explain why many people over the age of 60, who likely were exposed to similar viruses earlier in life, carry antibodies or other type of immunity against H1N1. These immune responses could be attributed to earlier flu exposure and vaccinations.

"These findings indicate that human populations may have some level of existing immunity to the pandemic H1N1 influenza and may explain why the 2009 H1N1-related symptoms have been generally mild," explains Carol Cardona, a veterinarian and Cooperative Extension specialist.

Adds project scientist Zheng Xing: "Our hypothesis, based on the application of data collected by other researchers, suggests that cell-mediated immunity, as opposed to antibodymediated immunity, may play a key role in lowering the disease-causing ability--or pathogenicity--of the 2009 H1N1 influenza." He notes that...