The host makes all the difference( Where there are many scientific wo...)

"Where there are many scientific works dealing solely with the flu virus, we have investigated how the host reacts to an infection," says Klaus Schughart, head of the Experimental Mouse Genetics research group. In infection experiments the researchers have now discovered that an excessive immune response is responsible for the fatal outcome of the disease in mice. This overreaction has genetic roots. The findings have now been published in the scientific magazine PLoS One.

For their investigations the researchers injected seven different inbred mouse strains with the same quantity of type Influenza A flu viruses. All of the animals within one mouse strain are genetically identical, like identical twins. However, one strain differs from another just like different individuals in the human population. To their surprise, the researchers were able to identify strong differences in the progression of the influenza between the seven strains. In five of the strains the illness was mild: the animals lost weight, recovering completely after seven to eight days. However, in two of the mouse strains the animals lost weight rapidly and died after just a few days.

The researchers looked for reasons for these differences: they investigated how the immune system of the animals responds to the virus. "The mice die from their own immune defences, which are actually supposed to protect them against the virus. The immune system produces too many messengers, which have a strong activating effect on the immune cells. These cells then kill tissue cells in the lungs that are infected with the virus," says Schughart. At the same time, these overactive cells also destroy healthy lung tissue. In mice that died the researchers also found one hundred times more viruses than in animals that survived. "It appears that the animals have specific receptors on their cells that make them more receptive to a severe viral infection." Flu infections in humans could take a
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