And that may explain why the disease hasn't posed more problems, study says
MONDAY, Nov. 16 (HealthDay News) -- The swine flu virus that's sweeping across the United States isn't a total stranger to your immune system, a new study shows -- a finding that should ease the most drastic worries about the lethality of the pandemic.
"What has been widely reported in the general press is that the swine flu is totally new, so there is no immunity to it," said study lead author Bjoern Peters, an assistant member of the division of vaccine discovery at the La Jolla Institute for Allergy and Immunology in La Jolla, Calif. "But the severity of infections that have been seen is not greater than usually seen in seasonal flu."
The reason why the swine flu virus -- officially designated H1N1 -- isn't the killer it was feared seems to be that the various protective mechanisms of the immune system have been primed by exposure to previous flu viruses, said study co-author Alessandro Sette, director of the La Jolla Institute's Center for Infectious Disease.
Peters, Sette and their colleagues used a major flu database funded by the U.S. National Institutes of Health to look at the reaction of immune system cells to the H1N1 swine flu virus. They found that 17 percent of the B cells that attack viruses in the bloodstream recognized H1N1 because of exposure to other flu viruses.
"They produce antibodies in the bloodstream and try to find the virus before it ends up in cells, so they are what prevents the disease," Peters said.
And 69 percent of T cells, which attack the virus in infected cells, were alerted by those previous infections, the study found.
"They recognize the virus inside cells, so they are responsible for clearing the infection once you have it," Peters said. "Nobody knows what level of immunity is sufficient for protection. But if infected, our data suggest that T cells in those who have prev
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