When we think of bacteria, we tend to focus on their pathogenicity and ability to cause diseases such as tuberculosis, which infects around one-quarter of the world’s population. However, whilst bacteria do have the potential to become parasitic, if the trillions of bacterial cells that make up the human microbiome ceased to exist, human health would experience a rapid decline.

 

One reason for this is due to the critical role bacteria play in inducing the immune system against pathogenic threats. Upon viral infection, the interferon (IFN) defence system is initiated where the synthesis of antiviral cytokines is upregulated. Evidence suggests bacteria in the gut are capable of modulating the IFN system. They work by inducing macrophages and plasmacytoid dendritic cells to express type 1 IFN, which in turn primes natural killer cells and prepares cytotoxic CD8+ T cells for action. Erttmann et al (2022) demonstrate that a depletion of the gut microbiota diminishes the cell signalling pathways modulated by these commensal bacteria. This causes a reduction in type 1 IFN production, and thus an impairment in the activation of NK and CD8+ T cells. As a result, the body becomes more susceptible to attack by viral infections and less able to defend itself. This highlights just how vital the role bacteria in our microbiome play in providing us with innate immunity against viral pathogens and protecting our health.

 

This also brings attention to our use of antibiotics, and the potential negative effects they may have on the commensal bacteria residing in our body. Erttmann et al (2022) further showed that mice treated with a variety of antibiotics exhibited a major reduction in gut microbiota diversity, thus severely comprising their ability to fight off viral infections. Research like this is important in informing doctors to be sensible in their administration of antibiotics, as well as informing patients to not self-medicate and unnecessarily ingest antibiotics. Ultimately, the commensal bacteria living in our bodies play essential roles in protecting human health, and it is, therefore, vital we take the necessary steps to also protect these remarkable microorganisms in return.

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By Bisma Butt

 

REFERENCES 

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Erttmann, S.F., Swacha, P., Aung, K.M., Brindefalk, B., Jiang, H., Härtlova, A., Uhlin, B.E., Wai, S.N. and Gekara, N.O., 2022. The gut microbiota prime systemic antiviral immunity via the cGAS-STING-IFN-I axis. Immunity, 55(5), pp.847-861.

 

Ganal, S.C., Sanos, S.L., Kallfass, C., Oberle, K., Johner, C., Kirschning, C., Lienenklaus, S., Weiss, S., Staeheli, P., Aichele, P. and Diefenbach, A., 2012. Priming of natural killer cells by nonmucosal mononuclear phagocytes requires instructive signals from commensal microbiota. Immunity, 37(1), pp.171-186.

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