Why Some People Shake Off The Flu In A Couple Of Days, While Others Suffer Longe

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Why Some People Shake Off The Flu In A Couple Of Days, While Others Suffer

Longer, Or Die

ScienceDaily (Mar. 26, 2009) — For some people it is a certainty: as soon as the

annual flu season gets underway, they are sure to go down with it. It is little

comfort to know that there are other people who are apparently resistant to flu

or overcome the illness after just a couple of days. It is this phenomenon that

is now being investigated by researchers at the Helmholtz Center for Infection

Research, using various strains of mice.

" 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.

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 similar course, here too, genetic factors could favour a

severe progression of the illness. " It is only now that we are beginning to

understand the role played by the genetic factors of the host and what increased

receptiveness means in the case of influenza, " says Schughart.

Every year between 10,000 and 30,000 people in Germany die from influenza, the

majority via pathogens of the Influenza A type. There are various sub-types of

the main type A, in which the composition of the virus envelope differs. H1N1

and H3N2 are the most widely-distributed flu strains amongst humans, H5N1 the

familiar avian flu virus. The H stands for the protein haemagglutinin, with

which the virus latches onto the cells of the airways, infecting them. In order

for the newly-created flu viruses to leave the host cells, in turn, they require

neuraminidase (N). To evade an immune response the virus changes the H and N

characteristics constantly. Sometimes light, sometimes heavy: the result is a

completely new virus type with a new number, with the consequences generally a

severe global flu pandemic.

Journal reference:

1. Srivastava et al. Host Genetic Background Strongly Influences the Response

to Influenza A Virus Infections. PLoS ONE, 2009; 4 (3): e4857 DOI:

10.1371/journal.pone.0004857

Adapted from materials provided by Helmholtz Association of German Research

Centres, via EurekAlert!, a service of AAAS.

http://www.sciencedaily.com/releases/2009/03/090326100706.htm