Scientists talked about the role of respiratory tract bacteria in protecting the lungs
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- Scientists talked about the role of respiratory tract bacteria in protecting the lungs
A common bacterium of the oral cavity and respiratory tract can help immune cells more effectively deal with one of the main causative agents of bacterial pneumonia. In experiments on mice, pre-exposure to Prevotella melaninogenica altered the function of protective cells and improved the destruction of pneumococcus. How microorganisms of the respiratory tract interact with the immune system and what this may mean for the future prevention of infections — in the Izvestia material.
Bacteria may be involved in protecting the lungs
Pneumonia develops with an infectious lesion of the lungs. Inflammation affects the alveoli, small air sacs through which gas exchange occurs. They can fill with fluid or pus, and the disease is accompanied by coughing, fever, and difficulty breathing. The cause can be bacteria, viruses, and fungi; the severity depends on the pathogen, age, and general health.
One of the main bacterial pathogens is Streptococcus pneumoniae, or pneumococcus. However, contact with him does not always end in severe infection. Researchers are trying to figure out which features of local protection help the body cope with the bacterium.
In the new work, attention was focused on the microbiome of the respiratory tract, the community of microorganisms living there. Scientists have studied whether exposure to one of the usual representatives of this community can change the subsequent response to the causative agent of pneumonia.
"Our lungs are constantly encountering bacteria from the mouth and upper respiratory tract, and these contacts can really help train the immune system," said Sarah Clark, senior author of the study and associate professor at the University of Colorado Anschutz School of Medicine.
In this case, "learning" refers to a change in the functioning of immune cells after contact with a microorganism. It can influence how effectively these cells will respond to a subsequent infection.
What is the Prevotella bacterium interested in?
Prevotella is one of the most common genera of bacteria found in healthy oral cavity and respiratory tract. A specific species was used in the study — Prevotella melaninogenica.
The combination of two symptoms does not yet show that one causes the other. The composition of the microbiome could be related to other features of the body or the course of the disease. To test the possible effect of the bacterium, an experiment was needed in which its effect preceded infection.
Scientists have raised the question of whether P. melaninogenica is able to change the state of the immune cells of the lungs so that they can better cope with pneumococcus.
How the protective effect was tested
The researchers first exposed mice to P. melaninogenica and then infected them with S. pneumoniae. After that, the amount of the pathogen in the lungs and changes in the work of immune cells were evaluated.
In animals previously exposed to Prevotella, the amount of pneumococcus in the lungs was significantly lower. The immune cells absorbed and destroyed the bacteria more efficiently.
This result is important for understanding the defense mechanism: the researchers found both changes in cell behavior and improved removal of the pathogen from the lungs. The effect concerned the response to subsequent infection, not just the reaction to initial contact with Prevotella.
The experiment was conducted on mice. He shows the possibility of such an interaction in an experimental model, but does not establish that a similar effect will prevent pneumonia in humans.
Which cells started working differently
The scientists paid special attention to neutrophils and macrophages. These cells are involved in protecting against infection and are able to absorb microorganisms. This process is called phagocytosis: the cell captures the bacterium, after which the mechanisms of its destruction are activated.
After exposure to Prevotella, mouse neutrophils and macrophages performed better against pneumococcus. Not only the number of protective cells changed, but also their functional state — the way they performed their work.
"There were more immune cells, and they behaved differently. Their functions have been reprogrammed so that they can better remove bacteria," Clarke explained.
In this context, "reprogramming" means changing the activity of cells and the biological processes involved in them. To assess protection, it is important not only the number of cells in the lungs, but also their ability to recognize, absorb and destroy the pathogen.
It is the combination of these changes that helps explain why prior contact with one bacterium could improve the response to another.
How scientists studied thousands of individual cells
To see the changes in more detail, the researchers used RNA sequencing of individual cells. This method allows us to determine which genes are active in each cell under study, based on the RNA molecules present in it.
The activity of genes is related to which proteins and signaling mechanisms the cell uses. Therefore, the analysis helps to compare its conditions: for example, what processes intensify after contact with a bacterium and what differences arise during infection.
The study of individual cells is especially useful for such a comparison. Different cell types are present in the lungs at the same time, and their response may vary. A general analysis of the tissue is able to combine these changes, while studying the cells individually allows you to more accurately determine where they occur.
The scientists analyzed thousands of lung cells and found that exposure to Prevotella altered the state of several types of immune cells involved in fighting infection. These data complemented the results of the assessment of pneumococcal eradication.
What does this say about the microbiome of the respiratory tract
The results support the idea that common respiratory tract microorganisms may be involved in regulating the local immune response. Their role is not limited to their presence next to body cells: contact with them can change the work of protective mechanisms.
In this experiment, one bacterium influenced how immune cells responded to another microorganism. This relationship provides a possible biological explanation for clinical observations in which the features of the respiratory microbiome were combined with a more favorable course of the disease.
However, the results do not allow us to divide all the bacteria of the respiratory tract into unambiguously beneficial and harmful. The study is devoted to a specific Prevotella species, a specific pathogen, and specified experimental conditions.
It also does not follow that increasing the total number of bacteria in the respiratory tract will improve protection. For further work, it is important to establish exactly which interactions help immune cells, under what conditions they occur, and how safe it is to manage them.
Can the discovery help prevent pneumonia?
Researchers are interested in the possibility of using the natural interaction of the microbiome and the immune system to prevent respiratory infections. If it is possible to determine how bacteria alter the response of protective cells, this may point to new approaches to prevention.
The perspective is primarily related to understanding the mechanism. It is necessary to find out which signals trigger beneficial changes, how long the effect lasts, and whether it can be safely reproduced in humans. The question of whether such protection will work against other pathogens is also important. Based on the experience with mice, it is not yet possible to determine an effective prevention scheme for humans. This requires further research, followed by a clinical assessment of safety and outcome.
At the same time, existing preventive measures have an independent evidence-based basis. According to the US Centers for Disease Control and Prevention (CDC), vaccination can prevent infections caused by certain pathogens of pneumonia. Hygiene, smoking cessation, and chronic disease control also contribute to reducing risk.
Переведено сервисом «Яндекс Переводчик»
