The most significant finding of the Japanese study was identification of a rare immune system cell type, dendritic, or plasmacytoid, plasma cells, which control the effect of inactivated flu virus vaccines, Ishii said. The study showed that those cells play no role in the response to split-virus vaccines, "thereby enabling us to understand why and how different flu vaccines work or sometimes do not work well," he said.
"We know that these dendritic cells are extremely sensitive to viral RNA," Topham said. "They have different ways of recognizing viruses."
RNA is the genetic material of influenza viruses.
While the Japanese work "doesn't contain a whole lot of things we didn't know before," Topham said, it does present a valuable map of the flu vaccine territory.
"Our findings certainly help clinicians understand why one shot of the swine flu vaccine worked well and why seasonal vaccines do not work well in children," Ishii said.
Flu viruses and vaccines against them are described by the U.S. Centers for Disease Control and Prevention.
SOURCES: Ken J. Ishii, M.D., Ph.D., adjunct professor, Osaka University Laboratory of Vaccine Science, Suita, Japan; David Topham, Ph.D., associate professor, microbiology and immunology, University of Rochester, Rochester, N.Y.; March 31, 2010, Science Translational Medicine
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