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Asthma: a "health" effect of lung bacteria demonstrated for the first time
INRA scientists*, working in collaboration with their colleagues from Ghent University (Belgium) have revealed for the first time that certain bacteria in the lungs may be associated with beneficial or harmful effects on asthma. This work, published in The ISME Journal on 3 January 2017, shows that the microbial community present in the lungs (pulmonary microbiota) constitutes an as yet unexplored source of bacteria, or substances produced by bacteria, which could attenuate certain respiratory diseases such as asthma.
Asthma is a chronic respiratory disease for which symptomatic treatments are available, but no universal cure yet exists. The incidence of this disease has increased in recent years; it now affects one child and one adult in ten, and constitutes a major public health challenge. Asthma may be triggered by exposure to respiratory allergens such as dust, mites, moulds or pollens, etc.
The lung microbiota has only recently been described, as the lungs were long considered to be a sterile organ. The influence of the lung bacterial microbiota on the respiratory epithelium, the development of immunity and the severity of asthma are innovative areas on which INRA scientists focused at a very early stage. Until now, no micro-organisms resident in the lungs had been associated with either beneficial or harmful effects on lung immunity.
Lung bacteria with effects on health
During this study, the scientists described the lungs of two types of mice: those reared under sterile conditions (axenic or germ-free) and those reared in a normal environment in contact with micro-organisms. The lungs of the axenic mice exhibited differences regarding the level of expression of certain genes when compared with those of the normal mice. This finding suggests that the environment in which we have grown up may affect the defensive capabilities of our lungs.
Bacteria colonise the lungs gradually as from birth, and this accompanies maturation of lung immune defences. The neonatal period therefore provides an excellent window for intervention in order to prevent or reduce the impact of childhood respiratory diseases. To study the protective effects (or not) of lung bacteria against asthma, the scientists cultivated and characterised bacterial strains isolated from the lungs of disease-free mice. Three strains of micro-organisms were retained and were then administered separately, by intranasal inoculation, in mouse pups, before the animals breathed in mite allergens.
One strain had a neutral (no) effect on the disease, while another diminished the symptoms in the pups and another exacerbated the asthma.
This work has thus shown that lung bacteria constitute an as yet unexplored source of bacteria, or substances produced by bacteria, which could attenuate certain respiratory diseases such as asthma. A patent has been filed relative to the applications in respiratory health of certain lung bacteria.
The scientists are now pursuing their work, notably in order to determine whether these lung bacteria could change the susceptibility to respiratory disorders of neonates.
*Scientists from two INRA units (Jouy-en-Josas) were involved in this work: the Joint Research Unit for Food and Gut Microbiology for Human Health and the Molecular Virology and Immunology Research Unit.
Aude Remot, Delphyne Descamps, Marie-Louise Noordine, Abdelhak Boukadiri, Elliot Mathieu, Véronique Robert, Sabine Riffault, Bart Lambrecht, Philippe Langella, Hamida Hammad and Muriel Thomas Bacteria isolated from lung modulate asthma susceptibility in mice, The ISME Journal advance online publication 3 January 2017; doi: 10.1038/ismej.2016.181