(A–C) Mice with indicated genotypes (control, Aldh1a1^+/+ or Aldh1a1^+/–; KO, Aldh1a1^–/–) were intraperitoneally injected with 200 mg/kg naphthalene at 2-week intervals for a total of 2 times or were intranasally injected with 100 μg DEPs every other day for a total of 6 times. (A and B) Two weeks after the secondary naphthalene administration (A) or 3 days after the DEP administration (B), mucociliary transport in isolated tracheas was determined using live imaging of fluorescent beads. Each bead is assigned a specific color, and the motion of these beads over a 1-second time frame is demonstrated (upper). Trajectory uniformity calculated from 10 beads per recorded area (lower left) and path linearity of individual beads (lower right) are presented. Each dot represents one mouse, and the mean values are shown by red horizontal lines (A, n = 3–5; B, n = 4–9). Scale bars: 10 μm. (C) Two weeks after the second naphthalene injection, mice were intranasally injected with fluorescent microbeads, and bead accumulation in lung tissues was measured by IVIS at 24 hours after injection. Upper: Representative images of indicated genotypes with naphthalene exposure. Lower: Fluorescence intensity is shown. Each plot represents one mouse, and the mean values are shown by red horizontal lines (n = 3–9). (B and F) Mice with indicated genotypes were intranasally infected with 1 × 10⁸ CFU of S. pneumoniae. Schematic of experimental design (upper) and survival (lower) without any pre-exposure (D, n = 9–16), with naphthalene administration (E, n = 12–14), or with DEP administration (F, n = 28–29) are shown. ****P < 0.001, ***P < 0.01, **P < 0.02, *P < 0.05, and NS, not significant by 1-way ANOVA followed by post hoc Tukey’s test (A–C) or Kaplan-Meier survival analysis (D–F). Data represent at least 2 independent experiments with similar results (A–C).