Fig. 1.

The presence of oral bacteria-induced PAFR, ACE2, and MUC5AC expression in alveolar epithelial cells and proinflammatory cytokine secretion and MUC5AC expression in murine lungs.

(A) When alveolar epithelial cells were incubated with the periodontal pathogen P. gingivalis, PAFR expression was induced in the cells at the gene level after 24 h [25].

(B) When F. nucleatum was introduced into the trachea of mice, a much larger amount of IL-6 and KC (IL-8 isoform in mice) was induced in the lungs and blood than when Streptococcus pneumoniae was introduced [27].

(C) When the culture supernatant of the P. gingivalis parent strain was introduced into mouse bronchi (Top), MUC5AC was induced in airway epithelia in the mouse lungs (brown), but no such phenomenon was observed with P. gingivalis gingipain-deficient (Kgp/Rgp(-)) mutant strains [30].

(D) When alveolar epithelial cells were incubated with the periodontal pathogen F. nucleatum, ACE2 expression was induced in the cells at the protein level [35].