The global spread of antibiotic-resistant bacteria is spurring the introduction of phage therapy into clinical practice—a method of treating bacterial infections using bacteriophages, bacteria's natural enemies. The effectiveness of phages in treating various infections has been repeatedly proven. However, a number of questions remain about the mechanisms by which phages kill bacteria in vivo , particularly the influence of the host's immune system on this process.

A team of scientists from the Institut Pasteur (France) studied* the influence of host immunity on the effectiveness of phage therapy for acute pneumonia caused by a multidrug-resistant strain of Pseudomonas aeruginosa in mice. The experiments compared the effectiveness of therapeutic and prophylactic use of specific bacteriophages in healthy immunocompetent mice and animals deficient in certain immune factors (MyD88, lymphocytes, neutrophils).

Synergy between neutrophils and bacteriophages has been shown to be critical for the successful treatment of acute pneumonia. Neutrophils, in particular, are involved in the elimination of bacterial variants that have become resistant to the phage preparation being used.

Thus, the effectiveness of phage therapy may be due not only to the phage's ability to kill bacteria, but also to so-called "immuno-phage" synergism.

It is important to note that during the treatment process, the therapeutic phages themselves were not destroyed by the host's lung immune effector cells and did not cause immune reactions in the lungs.

* Roach DR, Leung CY, Henry M et al. Synergy between the Host Immune System and Bacteriophage Is Essential for Successful Phage Therapy against an Acute Respiratory Pathogen // Cell Host & Microbe, 2017, 22(1): 38-47.E4 . DOI:https://doi.org/10.1016/j.chom.2017.06.018