Modifying Brain's Immune Response to Kill Tumors

Virologists have discovered why avian flu has so far failed to spread from person to person despite being able to flourish in human lung tissue: a lack of receptors to bind to the virus.

Investigators at the University of Wisconsin (Madison, USA; www.wisc.edu) worked with cultures of human cells taken from various portions of the respiratory track. By monitoring the ability of the virus to bind to the cells, they were able to show that cells from the upper portions of the respiratory system lacked surface receptors for binding to the avian H5N1 virus. They reported in the March 23, 2006, issue of Nature that avian flu requires a binding site for sialic acid linked to galactose by an alpha-2,3 linkage, while human influenza virus requires an alpha-2,6 linkage.

"Deep in the respiratory system, (cell) receptors for avian viruses, including avian H5N1 viruses, are present,” explained senior author Dr. Yoshihiro Kawaoka, professor of pathobiologic sciences at the University of Wisconsin. "But these receptors are rare in the upper portion of the respiratory system. For the viruses to be transmitted efficiently, they have to multiply in the upper portion of the respiratory system so that they can be transmitted by coughing and sneezing. No one knows whether the virus will evolve into a pandemic strain, but flu viruses constantly change. Certainly, multiple mutations need to be accumulated for the H5N1 virus to become a pandemic strain.”



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