Trout teaches us more about our microbiota

While most scientists study mice, trout can also teach us things about our bodies. More specifically, rainbow trout, analyzed by researchers from the University of Pennsylvania (United States). Indeed, they discovered that a particular type of antibody plays an essential role in the fight against disease and the preservation of the microbiome. Have studies that addressed the following question: evolved mucosal antibodies – those present on the mucosal surfaces of the body like the intestine in humans or gills in fish – to fight pathogens and preserve a healthy microbiota? Their results are published in the journal Science Immunology.

Reduce bad microbes, keep good bacteria

American researchers have indeed discovered that a mucosal antibody, an immunoglobulin, plays this essential role. “We have found that it plays two paradoxical roles: on the one hand, reducing bad microbes and, on the other hand, promoting the presence of certain beneficial bacteriasays J. Oriol Sunyer, a researcher at the Penn’s School of Vetenary Medicine and author of the study. Fish are the first vertebrates to have a mucosal immune system, and therefore the fact that they have a specialized immunoglobulin that performs both functions suggests that these two processes are so fundamentally important for the survival of vertebrates, that they appeared simultaneously , and early in the evolution. ” In fish, this immunoglobulin is called IgT. In mammals, this corresponds to the immunoglobulin IgA.

Without immunoglobulin, damage and inflammation

“In recent years, some key studies have shown that IgA is needed to control the mammalian microbiome. In mice and humans without IgA, their microbiome changes: beneficial bacteria decrease and potentially pathogenic bacteria increase ”, explains Sunyer. However, this work has never demonstrated the precise role of IgA in the preservation of the microbiome. So, with his team, J. Oriol Sunyer developed an adult fish model in which the IgT resources were exhausted for two months. The researchers then found that the presence of a mucous parasite increased considerably. In addition, in fish lacking IgT immunoglobulin, bacteria have “escaped” from the surface of the gills to enter the tissue and cause damage and inflammation. Thus, the researchers found in these fish a dysbiosis, that is to say an imbalance of the bacterial ecosystem.

The microbiome has a recovery capacity

The advantage is that soon after the study, IgT levels returned to normal. The researchers thus observed a real “recovery” of the microbiome, a return to normal. “In microbiome studies, recovery is a very important pointsays Sunyer. When you take an antibiotic, you can disrupt your microbiome as recovery can take time. The disturbance we used to remove IgT had a profound but transient effect on the composition of the microbiome, which underwent rapid recovery. ” This study thus demonstrates that working on mammals is not enough to understand the role of the microbiome and its functioning. In addition, Sunyer believes that this work could promote the use of specific species of fish bacteria as probiotics, in order to stimulate the immune system.

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