5. NASOPHARYNGEAL BACTERIAL COMMUNITY AS A SHIELD AGAINST
RESPIRATORY INFECTIONS
Nasopharyngeal bacteria may counteract bacterial or viral infection. In
infant mice, nasal priming with viable Corynebacterium
pseudodiphtheriticum , a Gram-positive bacterium member of the normal
microbiota of the upper respiratory tract, improved their resistance to
primary RSV infection and secondary pneumococcal pneumonia
[52]. The
protection against RSV infection
and pneumococcal superinfection was related to modulation of Toll-like
receptor 3 activation in the respiratory tract leading to enhanced
production of the protective cytokines TNF‐α, IL‐6, IFN‐γ and IFN-β, but
also of IL-10 that could contribute to restrict the inflammatory
reaction and ultimately to limit tissue injury. IFN-γ producing CD3+CD4+
cells were also detected in the lungs of treated infant mice, viral load
was significantly lower and lung tissue damage markers (LDH and albumin
concentrations) in bronchoalveolar lavage were decrease in RSV-infected
mice. Priming with viable Corynebacterium pseudodiphtheriticumalso reduced lung bacterial cell counts and prevented the dissemination
of S. pneumoniae into the blood [52]. Thus, a possible
perspective use of these results could be a seasonal application of a
nasal probiotic spray to boost respiratory innate immunity in
immunocompetent subjects. Bearing in mind the “gut-lung axis”
interaction, one could consider orally given probiotics or bacterial
derived products as alternative options; a fascinating proposal whose
theoretical efficacy needs eventually to be demonstrated by further
studies [53]. A possible approach can be to assess bacterial lysate
in germ free mice models to determine the effect on immune maturation
and the capacity to mimic the microbiota effect in respiratory virus
infection.