Until recently, bacteriophages (phages) were viewed merely as "bacteria eaters" that could be useful in the fight against multidrug-resistant infections. However, research into phage biology is revealing new potential applications in medical practice. In particular, data has accumulated on the immunomodulatory and anti-inflammatory properties of phages*.

Our knowledge of the role of phages in the human body, their impact on health, and the development of diseases is gradually expanding. Phages are present in large numbers in the digestive tract and are often detected in urine and saliva. According to metagenomic analysis, phages also circulate in the blood.

The greatest diversity of phages is characteristic of the intestine. It was once hypothesized that intestinal phages, via transcytosis, could enter the lymph, blood, and other tissues and perform immunomodulatory functions there. This idea was subsequently confirmed and developed by JJ Barr (2017)**, who proposed the concept of the "phageome" (analogous to "genome," "proteome," and "microbiome") and suggested that approximately 30 billion phages migrate daily from the intestine to tissues. The constant presence of phages in the human body provides protection against infections, which has already been dubbed "natural phage therapy."***

Data obtained from in vitro and in vivo experiments indicate that phages do not harm eukaryotic cells. Experience with phage therapy in Poland and the former Soviet Union, as well as the results of recent trials in Europe and the United States, demonstrate that phages are nontoxic to mammals and do not affect the function of internal organs. At the same time, phages are known to interact with the immune system. They can induce antibody production, but more often they modulate the immune response, specifically by reducing immune hyperactivity. This latter approach has potential applications in the treatment of autoimmune diseases, preventing transplant rejection, and other areas.

The combination of antibacterial, immunomodulatory and anti-inflammatory properties of phages opens up prospects for their use in the treatment of diseases that are difficult to treat, such as sepsis, inflammatory bowel disease and even allergic diseases .

* Górski A, Jończyk-Matysiak E, Międzybrodzki R et al. Phage Therapy: Beyond Antibacterial Action // Front Med (Lausanne), 2018; 5: 146. doi: 10.3389/fmed.2018.00146

**Barr JJ. A bacteriophages journey through the human body // Immunol Rev., 2017, 279:106–122. https://doi.org/10.1111/imr.12565

*** Guglielmi G. Do bacteriophage guests protect human health? // Science, 2017, 358(6366): 982-983. DOI: 10.1126/science.358.6366.982