Evolution: the newly-found bacterial role: (Evolution)

by David Turell , Tuesday, May 12, 2020, 18:56 (1654 days ago) @ David Turell

They are here to stimulate the immune system, when it is not being stimulated, keeping it on the ready:

https://medicalxpress.com/news/2020-05-microbiome-immune.html

"Working alongside colleagues in Mainz, Bern, Hannover and Bonn, researchers ... were able to show how the microbiome helps to render the immune system capable of responding to pathogens. If microbiome-derived signals are absent, relevant mediators are not released, resulting in a failure to activate metabolic processes in certain immune cells. According to the researchers' report, which has been published in Cell, this leaves the relevant cells without the necessary fuel to mount an immune response.

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"Presence of an infection triggers the body's immune response. A key role in this process is played by conventional dendritic cells (CDCs). These form part of the body's innate immune system and carry a range of pattern recognition receptors that enable them to detect invading pathogens quickly. The cells' initial response involves the release of cytokines, signaling proteins that attract immune cells to the site of infection. At the same time, these cells also use phagocytosis to engulf and digest invasive pathogens, after which they present individual particles as antigens on their cell surface. This, in turn, leads to the activation of T cells, which form part of the adaptive immune system, and results in a targeted immune response. In contrast, when T cell activation is triggered by CDCs presenting endogenous antigens, it leads to a faulty and undesirable immune response and results in autoimmune diseases.

"The team of researchers led by Prof. Diefenbach found that CDCs are incapable of triggering immune responses in sterile conditions (i.e., in germ-free mice). The researchers concluded that CDCs must receive information while the cell is in its basal state, which is characterized by the absence of infection, and that this information must derive from the microbiome. These microbiome-derived signals prime CDCs for a future response against pathogens.

"'We want to understand the nature of the microbiome's continuous effects on CDC function," says Prof. Diefenbach. "In this study, we were able to show that in their basal state, these specialist immune cells are subject to the uninterrupted microbiome-controlled signaling of type I interferons (IFN-I)."

"Interferons are cytokines, special signaling molecules known to play a role in antiviral activity. "Until now, we had known only little about the role of IFN-I in the basal state. CDCs that do not receive this IFN-I signaling during the basal state cannot fulfill the physiological functions they perform as part of the body's fight against pathogens," says the microbiologist. Study results suggest that the microbiome controls the immune system's fitness. It exerts this control by bringing the immune system to a state of 'readiness' in order to speed up its response to pathogens.

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"Describing the researchers' observations, the study's first author, Laura Schaupp, says, "Interestingly, when we looked at CDCs from germ-free animals and those without IFN-I signaling, we were able to observe low levels of expression among genes involved in the mitochondrial respiratory chain. Further analyses revealed that the cellular metabolism of CDCs from germ-free animals is dysfunctional, making them unable to initiate an immune response. The cells effectively lack the fuel needed to respond to pathogens." This suggests that the microbiome is of crucial importance to the functioning of CDCs. It appears essential to the ability of CDCs to mount an effective response to bacterial or viral infections, including responses mediated by T cells."

Comment: We see an other reason why bacteria were at the start and are still here to manage readiness for immune systems, even when they are idle without a challenge. Looks like a great plan to me.