The macrophages are immune system cells capable of ingesting waste, such as damaged cells, and large pathogens, a «key» function in maintaining and ensuring the proper functioning of the body’s tissues, although scientists are still unclear about the importance of the energy they obtain in the process.
«It is the first time that this ability of macrophages has been demonstrated. Our work suggests that it is important for macrophages that have this phagocytosis capacity. For the immune system in general, it cannot yet be said,» said Johan Garaude, researcher at Inserm and lead author of the study published in the journal ‘Nature’, in collaboration with CNIO.
The researcher explained that in normal conditions, macrophages ‘eat’ only some bacteria, but when there is an infection, macrophages «can ‘eat’ up to a hundred bacteria without problems,» something that they have been able to verify ‘in vitro’.
This work also shows that macrophages extract nutrients «more efficiently» from dead bacteria than from live ones, all after comparing the metabolism of these cells in different environments, such as with live bacteria, dead bacteria, and in the presence of a component of the bacterial membrane known to activate these cells.
«The macrophages that have phagocytized whole bacteria, whether alive or dead, have a very different metabolism from those that have been activated only by the bacterial membrane. This suggests that macrophages use bacteria as a source of nutrients to maintain their own metabolism and also to ensure the specificity of their function in the immune system,» explained Garaude.
Furthermore, they have observed how macrophages that have digested dead bacteria are «much more likely» to survive in a nutrient-poor environment, a difference that «could favor» the survival of macrophages in the case of an infection, as in infected tissues there is a scarcity of nutrients due to bacteria, which «reproduce rapidly,» having already consumed them.
Although the importance of this mechanism in bacterial infections still needs to be explored, scientists have pointed out that these results «open up new avenues» to combat antibiotic resistance or for innovative approaches in the field of vaccines.
«The idea would be to add certain metabolites to direct the action of the immune system. By adding metabolites, the immune response required in a vaccine could be modified (supported or inhibited), whether for infections or in the case of immunotherapy against cancer or inflammatory diseases,» added Garaude.
On the other hand, the head of the Cell Signaling and Metabolism Group at CNIO, Alejo Efeyan, detailed that when macrophages break down a pathogen, they also «recycle its components, in the form of nutrients and energy that are later used by the immune cell.»
Efeyan also stated that his role was «to help understand how the cellular digestion machinery and the detection of recycled nutrients are important for this recycling process to function, and to fine-tune the immune response.»
Likewise, he emphasized that understanding that recycling varies depending on whether the ingested bacteria are alive or dead «is of utmost importance, because an active infection is much more alarming for the immune system than a controlled one,» as macrophages «produce messages that attract more defensive cells» when digesting a live bacteria.
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