AsianScientist (Aug. 30, 2017) - In a study published in Cell Stem Cell, scientists in Japan and Switzerland have found that bacterial infections can stress blood-producing stem cells in the bone marrow and reduce their ability to self-replicate.

When a person becomes infected with a virus or bacteria, immune cells in the blood or lymph react to the infection. Some of these immune cells use sensors on their surfaces, called Toll-like receptors (TLR), to distinguish invading pathogens from molecules that are expressed by the host. By doing so, they can attack and ultimately destroy pathogens thereby protecting the body without attacking host cells.

Bone marrow contains hematopoietic stem cells which create blood cells, such as lymphocytes and erythrocytes, throughout the lifetime of an individual. When infection occurs, a large number of immune cells are activated and consumed. Hence, it is necessary to replenish these immune cells by increasing blood production in bone marrow.

Recent studies have revealed that immune cells are not the only cells that detect the danger signals associated with infection. Hematopoietic stem cells also identify these signals and use them to adjust blood production. However, little was known about how hematopoietic stem cells respond to bacterial infection or how it affected their function.

In this study, researchers from Kumamoto University and the University of Zurich analyzed the role of TLRs in hematopoietic stem cells upon bacterial infection, given that both immune cells and hematopoietic stem cells have TLRs.

To generate a model of bacterial infection, researchers injected one of the key molecules found in the outer membrane of gram negative bacteria and known to cause sepsislipopolysaccharide (LPS)into lab mice. They then analyzed the detailed role of TLRs in hematopoietic stem cell regulation by combining genetically modified animals that do not have TLR and related molecules, or agents that inhibit these molecules.

The results showed that LPS spread throughout the body, with some eventually reaching the bone marrow. This stimulated the TLRs of the hematopoietic stem cells and induced them to proliferate. They also discovered that while LPS promoted stem cell proliferation, it also induced stressed the stem cells, impairing their ability to successfully self-replicate and resulting in diminished blood production. Similar results were obtained after infection with Escherichia coli bacteria.

Fortunately we were able to confirm that this molecular reaction can be inhibited by drugs, said Professor Hitoshi Takizawa of Kumamoto University who led the study. The medication maintains the production of blood and immune cells without weakening the immune reaction against pathogenic bacteria. It might be possible to simultaneously prevent blood diseases and many bacterial infections in the future.

The article can be found at: Takizawa et al. (2017) Pathogen-Induced TLR4-TRIF Innate Immune Signaling in Hematopoietic Stem Cells Promotes Proliferation but Reduces Competitive Fitness.

Source: Kumamoto University.Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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Bacterial Infection Stresses Blood Stem Cells - Asian Scientist Magazine