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Influenza And Bacterial Pneumonia Make For Harmful Super-infection

Date:
March 20, 2009
Source:
Helmholtz Association of German Research Centres
Summary:
Influenza, or flu, is an unpleasant affair with fever, cough, as well as head and body ache. When this illness is further complicated by a bacterial pneumonia, a harmful super-infection develops. Until now, researchers thought that the flu facilitates an infection with pneumonia bacteria because it leads to a decrease of immune cells in the blood and thus impairs the body's defenses.

Influenza, or flu, is an unpleasant affair with fever, cough, as well as head and body ache. When this illness is further complicated by a bacterial pneumonia, a harmful super-infection develops. Until now, researchers thought that the flu facilitates an infection with pneumonia bacteria because it leads to a decrease of immune cells in the blood and thus impairs the body's defenses.

A joint venture from researchers from the Helmholtz-Centre for Infection Research (HZI) in Braunschweig, the Otto-von-Guericke-University in Magdeburg, and the Karolinska institute in Sweden have taken an in-depth look at the connection between flu infection and pneumonia. Their results have disproven a common theory about flu-like pneumonia.

Some viral infections trigger a decrease of immune cells in the blood – a so-called "lymphopenia". The reasons behind it and whether this is the case with influenza are unknown. To investigate the latter, HZI researchers infected mice with flu viruses and measured the amount of immune cells in the animal's blood every day. Some days later, flu-infected mice received a dosage of pneumonia bacteria usually harmless for healthy mice. While the flu-infected mice did develop a superinfection & subsequently died, surprisingly, they were not suffering from lymphopenia. The healthy, non-flu-infected mice defeated the bacteria successfully and recovered.

To discover whether a lack of immune cells encourages an infection with pneumonia bacteria in general, an artificial drug-induced lymphopenia was established in the mice. Without infecting these lymphopenic mice with flu viruses, they received pneumonia bacteria. Despite a severe lack of immune cells, the mice recovered completely.

With these results, the researchers could show that influenza facilitates and intensifies an infection from pneumonia bacteria, while disproving the common idea that this is caused by a lack of immune cells. "This result was an enormous surprise for us because it directly contradicts widespread assumptions", says Sabine Stegemann, researcher in the groups "Immune regulation" at the HZI and "Molecular Immunology" at the Otto-von-Guericke-University in Magdeburg.

"Now we want to understand the reasons for the increased susceptibility", says Matthias Gunzer, head of the group in Magdeburg. "It could be interplay of weakened mucous membranes and scavenger cells that induce ideal conditions for pneumonia bacteria to create a deadly lung infection. Another reason may be a reaction of the host immune system: It disables hyperactive flu-fighting immune cells to inhibit destruction of healthy lung tissue. "The immune system keeps itself under control and that makes it easy for pneumonia bacteria to infect the lung", says Gunzer.


Story Source:

The above story is based on materials provided by Helmholtz Association of German Research Centres. Note: Materials may be edited for content and length.


Journal Reference:

  1. Stegemann et al. Increased Susceptibility for Superinfection with Streptococcus pneumoniae during Influenza Virus Infection Is Not Caused by TLR7-Mediated Lymphopenia. PLoS ONE, 2009; 4 (3): e4840 DOI: 10.1371/journal.pone.0004840

Cite This Page:

Helmholtz Association of German Research Centres. "Influenza And Bacterial Pneumonia Make For Harmful Super-infection." ScienceDaily. ScienceDaily, 20 March 2009. <www.sciencedaily.com/releases/2009/03/090317111904.htm>.
Helmholtz Association of German Research Centres. (2009, March 20). Influenza And Bacterial Pneumonia Make For Harmful Super-infection. ScienceDaily. Retrieved July 28, 2014 from www.sciencedaily.com/releases/2009/03/090317111904.htm
Helmholtz Association of German Research Centres. "Influenza And Bacterial Pneumonia Make For Harmful Super-infection." ScienceDaily. www.sciencedaily.com/releases/2009/03/090317111904.htm (accessed July 28, 2014).

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