Rapid typing of carbohydrate receptors of influenza viruses pathogenic for humans

We are trying to find out which structures in the human respiratory airways influenza viruses bind to. We hope to be able to identify avian H5N1 viruses that could cause a human pandemic.

We know that to start infection, influenza viruses first need to bind to carbohydrate structures (receptors) on cells. Normally, human and avian viruses bind to different carbohydrates.

When the genes of avian viruses change or become mixed with genes of human viruses, they can switch to have preference for human cells. Human pandemic viruses can emerge in this way.

It is very challenging to detect and determine particular carbohydrate structures that the viruses bind to. This is because carbohydrates on cells are very diverse. They are like a forest containing innumerable trees with only a few specimens of each.

We have been developing a unique approach to identifying receptors among this vast range of carbohydrates. This is Carbohydrate Microarray Technology that involves spotting minute amounts of carbohydrates from cells onto a glass slide.

We are adapting the microarray technology to detect binding of the proteins known as haemagglutinins of different influenza viruses. We hope by this approach to be able to predict the pandemic potential of a given virus.

The emerging pandemic of influenza A H5N1 in feral and domestic avian species has affected some 30 countries to date from eastern Asia to Western Europe and northern Africa. The 169 confirmed human cases, with 91 fatalities, in 7 countries (to 13/02/06) emphasize the potential to cause a devastating pandemic. It is a high priority therefore to understand the mechanisms of emergence and risk of pandemic. The initial step in infection by the influenza virus is attachment of the virus particle to the surface of target cells through the interaction of the viral surface protein, haemagglutinin, with cell surface oligosaccharides that have terminal sialic acids. Understanding details of the oligosaccharide-binding specificities of influenza A viruses that infect humans and avians and have different tissue targets in the human will provide information crucial to gauging the pandemic risk posed by H5N1 and other subtypes. This project is focused on characterizing the range of host cell oligosaccharides that are attachment sites for prevailing and emergent influenza viruses that are pathogenic in the human in contradistinction to those of the avian and other mammalian influenza viruses that are not readily transmissible from an animal host to the human or from one person to another. Our laboratory has pioneered a carbohydrate microarray technology, and we have shown that it can be used for rapid screening of the interactions of soluble proteins, as well as virus particles, with the carbohydrate chains of glycoproteins and glycolipids. Coupled with mass spectrometry it is a validated approach for assigning novel carbohydrate ligands. Moreover our technology is unique in that it has provision for generating ?designer? microarrays from targeted tissues and secretions. Thus the specificities of binding (or adhesive footprints) of viruses can be determined for carbohydrate sequences that occur in the target host organs. Our aim is, in collaboration with Dr Alan Hay (World Influenza Centre NIMR) and Drs Steven Wharton and John Skehel (Virology Division NIMR), to apply our microarray technology with advanced mass spectrometry to characterize the distinctive carbohydrate sequences in human respiratory tract that are bound by influenza A viruses that are pathogenic in the human. An ultimate objective is to produce a microchip of arrayed oligosaccharide probes for the rapid typing of the binding ?footprints? of influenza virus isolates in order to survey for those that have preferred tropisms for the human and thus are a potential epidemiological hazard.