Viruses learn to trick immune system

April 28th, 2008 - 3:55 pm ICT by admin  

Washington, April 28 (IANS) Viruses use various tricks to invade cells and are now disguising themselves as cell wastes and tricking the body’s defences, says a new study. For example, vaccinia virus has a problem - it is a giant among viruses and needs a special strategy in order to infiltrate a cell and reproduce.

Ari Helenius and Jason Mercer from ETH Zurich’s Institute for Biochemistry have stumbled on new and surprising findings about how the virus exploits the cellular waste disposal mechanism.

When a cell dies, other cells ingest the remains, without needing waste disposal experts such as macrophages. The cells recognise the waste via a special molecule, phosphatidylserine, which sits on the inner surface of the double membrane of cells.

This special molecule is pushed out as soon as the cell dies and is broken into parts. Vaccinia virus itself also carries this official waste tag on its surface.

“The substance accumulates on the shell of vaccinia viruses,” Mercer explained.

The pathogen disguises itself as waste material and tricks cells into digesting it, just as they normally would with the remains of dead cells.

“The viruses are the Trojan horses that want to enter Troy; the Trojans are the many proteins that transmit the signals and open the ‘city gates’ to the unwelcome guest,” Ari Helenius said.

Aided by Lukas Pelkmans’ team, Mercer examined over 7,000 different proteins in order to find out not only which Trojans let the virus in, but which are chiefly involved in the supply chain.

Researchers de-activated the suspected proteins to examine their function and narrowed the vast number of proteins down to 140 potential culprits.

The enzyme kinase PAK1 turned out to be an especially “helpful” citizen of Troy. Without PAK1, the pathogen’s trick did not work.

Helenius is looking for substances that interrupt the signalling chain and halt the communication between the virus and the cell. If the cell does not ingest a virus, the virus cannot reproduce and is quickly eliminated by the immune system.

This process also has another big advantage. “Viruses cannot adapt to the obstruction of the signal chain all that quickly,” he said.

The research results have been published in Science.

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